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Insect Ecology and Population Dynamics
Introduction
Life does not exist in a vacuum Every living organism is surrounded by materials and
forces which constitutes its environment and from which it must derive its need Thus for its
survival a plant an animal or a microbe cannot live completely sealed in an impervious skin or
shell but requires from its environment-a supply of energy a supply of materials and a removal
of waste products For these basic requirements each living organism has to depend and also to
interact with different non-living or abiotic and living or biotic components of the environment
The biotic environmental components include basic inorganic elements and compounds such as
water and carbon dioxide calcium and oxygen carbonates and phosphates and an array of
organic compounds the by-products of organisms activity or death They also include such
physical factors as soil rainfall temperature moisture winds currents and solar radiation with
its concomitants of light and heat The biotic environmental factors comprise plants animals and
microbes all of which interact in a fundamentally energy-dependent fashion The scientific study
of the interactions of organisms with their physical environment and with each other is called
ecology (Helena Curtis 1975) It mainly occurs with the directive influences of abiotic and
biotic environmental factors over the growth distribution behavior and survival of organisms
(Herreid II 1977)
Definition
The author who was the first coin of the term ecology is uncertain however many
biologists grant credit to the German zoologist Ernst Haeckel who used the term as oekologie
in 1869 to refer to the inter-relationship of living organisms and their environment
The word ecology comes from two Greek words oikos meaning household or home
or place to live or habitation and logos meaning discourse or study Thus literally
ecology deals with the organism and its place to live Basically organisms place to live its
environment so ecology is also called environmental biology (Smith 1977)
Ecology is the scientific study of the relationships of living organisms with each other
and with their environments It is the science of biological interactions among individuals
populations and communities and also of ecosystems-the inter-relations of biotic communities
with their non-living environments
Insect Ecology and Population Dynamics
Conventionally ecology has been defined variously by different classical and modern
ecologists with different view of points Quite oddly no universally accepted definition of
ecology has been formulated by any ecologists so far and for the better understanding of scope
limitations purpose and mode of study of different ecological phenomena one has to go through
following chronologically arranged definitions of ecology
Ernst Haeckel (1869) defined ecology as the body of knowledge concerning the economy of
nature- the investigation of the total relations of animal to its inorganic and organic
environment
British ecologist Charles Elton (1927) defined ecology as the scientific natural history
concerned with the sociology and economics of animals
Taylor (1936) preferred to define ecology as the science of the relations of all organisms to all
their environments
A much broader definition of ecology of Allee et al (1949) considered ecology as the science
of inter-relation between living organisms and their environment including both the physical
and biotic environments and emphasizing inter-species as well as intra-species relations
SC Kendeigh (1961) defined ecology as the study of animals and plants in their relation to
each other and to their environment
Andrewartha (1961) defined ecology as the scientific study of the distribution and abundance
of animals
Odum (1963) defined ecology as the study of the structure and function of nature ecosystem
approach
GAPetrides (1968) defined ecology as the study of environmental interactions which control
the welfare of living things regulating their distribution abundance production and evolution
Krebs (1972) defined ecology as the scientific study of the interactions that determine the
distribution and abundance of organisms
Southwick (1976) defined ecology as the scientific study of the relationships of living
organisms with each other and with their environments He further elaborates his definition of
ecology by saying that it is the science of biological interactions among individuals
populations and communities and it is also the science of ecosystems-the inter-relations of
biotic communities with their non-living environments
Insect Ecology and Population Dynamics
Price (1984) defined ecology as the science of relationships of organisms to their environment
Insect ecology Insect ecology defined as the scientific study of the interactions (functional
process) that determine the distribution and abundance of true insects population in a specific
habitat
Objectives PurposesEcology is a distinct science because it is a body of knowledge not similarly organized in
any other division of biology because it uses s special set of techniques and procedures and
because it has a unique point of view The essence of ecology lies in the comprehensive
understanding of the meaning of following phenomena
1 The local and geographical distribution and abundance of organisms (habitat niche
community biogeography)
2 Temporal changes in the occurrence abundance and activities of organisms (seasonal
annual successional and geological)
3 The inter-relations between organisms in populations and their communities
(population ecology)
4 The structural adaptations and functional adjustments of organisms to their physical
environment (physiological ecology)
5 The behaviour of organisms under natural conditions (ethology)
6 The evolutionary development of all these inter-relations (evolutionary ecology)
7 The biological productivity of nature and its best use to mankind (ecosystem
ecology)
8 The conservation and management of natural resources (applied ecology)
Branches of ecologyEarly ecologists have recognized two major subdivisions of ecology in particular
reference to animal or to plants hence animal ecology and plant ecology But when it was
found that in the ecosystems plants and animals are very closely associated and inter-related
then both of these major ecological subdivisions became vague However when animals and
plants are given equal emphasis the term bioecology is used
Insect Ecology and Population Dynamics
Further ecology is often broadly divided into autecology and synecology Autecology
deals with the ecological study of one species of organism Thus an autecologist may study the
life history population dynamics behaviour home range and so on of a single species such as
the Maize-borer Chilo partellus Synecology deals with the ecological studies of communities or
entire ecosystems Thus a synecologist might study deserts or caves or tropical forests
Besides these major ecological subdivisions there are following specialized branches of ecology
1 Habitat ecology It deals with ecological study of different habitats on planet earth and
their effects on the organisms living
2 Organismal Ecology Evolutionary adaptations that enable individual organisms to
survive in their environment
3 Population Ecology Studies of the manner of growth density structure and regulation of
population of organisms and how members of a population coexists
4 Community Ecology Studies of the local distribution of animals in various habitats the
recognition and composition of community units and succession which indicate how
interactions between species (competition predation and symbiosis) affect community
structure and organization
5 Ecosystem Ecology Broadens to include the interactions of communities with all the
abiotic factors taken into consideration This branch of ecology often places research
emphasis upon energy flow and chemical cycling between living and non-living
components among and between communities
6 Biosphere Ecology The most complex level to study of ecology This is especially
a new field of study it has only recently become practical due to great advances
in satellite imagery of Earth global communication systems and breakdown of
national isolation which has allowed scientists from many countries to work
together and share results This is definitely he most interdisciplinary Ecological
Science it brings together scientific findings from many branches of science
including climatology oceanography meteorology soil science geology physics
chemistry and all the biological sciences
7 Evolutionary ecology It deals with the problems of niche segregation and speciation
8 Taxonomic ecology It is concerned with the ecology of different taxonomic groups of
living organisms and eventually includes following divisions of ecology microbial
Insect Ecology and Population Dynamics
ecology mammalian ecology insect ecology avian ecology parasitology human ecology
and so on
9 Applied ecology It deals with the application of ecological concepts to human need and
thus it includes following applications of ecology wild-life management range
management forestry conservation insect control epidemiology animal husbandry
aquaculture agriculture horticulture land use and pollution ecology
10 Production ecology It deals with the gross and net production of different
ecosystems like fresh water sea water agriculture horticulture etc and tries to do proper
management of these ecosystem so that maximum yield can be get from them
11 Physiological ecology The factors of environment have a direct bearing on the
functional aspects of organisms
12 Chemical ecology It concerns with the adaptations of animals of preferences of
particular organisms like insects to particular chemical substances
13 Space ecology It is a modern subdivision of ecology which is concerned with the
development of partially or completely regenerating ecosystems for supporting life of man
during long space flights or during extended exploration of extra-terrestrial environments
ScopeEcology is a multidisciplinary science and it includes not only the life sciences but
chemistry physics geology geography meteorology climatology hydrology palaeontology
archeology anthropology sociology and mathematics and statistics as well For explaining the
behaviour of an organism or biotic community in a given environment an ecologist has to
integrate the data which is obtained from many sources-morphology taxonomy genetics
physiology soil science climatology geology physics and chemistry
The scope of ecology is quite vast The study of ecological principles provides a
background for understanding the fundamental relationships of the natural community and also
the science dealing with particular environment such as forest soil ocean and inland waters
Many practical applications of this subject are found in agriculture horticulture forestry
limnology oceanography fishery biology biological survey pest control public
health toxicology pollution control conservation etc Ecological knowledge helps in
Insect Ecology and Population Dynamics
discovering new sources of food new unpolluting sources of energy and new methods of pest
control such as biological control which causes no environmental pollution
Some ecology related terminologyAbiotic factors Non-living ecological components of an ecosystem such water oxygen
sodium chloride nitrogen carbon dioxide etc and other physical and chemical influences such
as temperature light humidity pH etc
Biotic factors Living ecological components of an ecosystem such as producers
(chemosynthetic bacteria and photosynthetic green plants) consumers (heterotrophic animals
and decomposer organisms (bacteria fungi and other saprophytes)
Commensalism The living together of two species usually with benefit to one
Community A group of populations of plants and animals living together in a given place eg
the community of an oak forest a marsh a grassland a coral reef a desert etc
Competition Interaction occurs within interspecific or intraspecific population for utilizing
common resources that are in short supply (exploitation) or if the resources are not in short
supply for their survival or reproduction are known as competition
Consumers Organisms that ingest organic food (usually particulate) or other organisms
Dynamics In population ecology the study of reasons for changes in population size contrast
with statics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms
(biotic community) and non-living substances (abiotic environment) interacting to produce an
exchange of materials between the living and non-living parts
Habitat The natural abode of an organism including its total environment
Mutualism A interspecific relationship between two or more species in which both or all
benefit from the association and cannot live separately
Niche The ecological role or profession of an organism in its ecosystem its activities and
relationships to its community and total environment
Population Groups of individuals of single species a group of interacting individuals in a
definable space
Symbiosis The living together of two or more species
Insect Ecology and Population Dynamics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms (biotic
community) and non-living substances (abiotic environment) interacting to produce an exchange
of materials between the living and non-living parts It may be as small as a puddle or as large as
the entire earth Further an ecosystem may be natural as a pond a lake a river an estuary an
ocean a forest etc or it may be man-made or artificial like an aquarium a dam a cropland a
garden an orchard a city and so on The term ecosystem was coined by a Ag Tansley (1935)-
its eco part means environment and the system part implies a complex of coordinated units
Structure of an ecosystem
From structural point of view all ecosystems consists of following four basic
components
1 Abiotic Substances
2 Biotic Substances factors
a Producers
b Consumers
c Reducers or Decomposers
Biotic Substances
These include basic inorganic and organic compounds of the environment or habitat of
the organism The inorganic compounds of an ecosystem are carbon dioxide water nitrogen
calcium phosphate all of which are involved in matter cycles The organic compounds of an
ecosystem are proteins carbohydrates lipids and amino acids all of which are synthesized by
the biota of an ecosystem and are reached to ecosystem as their wastes dead remains etc The
climate temperature light soil etc are other abiotic components of the ecosystem
Producers
Producers are autotrophic organisms like chemosynthetic and photosynthetic bacteria
blue green algae algae and all other green plants They are called ecosystem producers because
they capture energy from non-organic sources especially light and store some of the energy in
the form of chemical bonds for the later use
Insect Ecology and Population Dynamics
Consumers
They are heterotrophic organisms in the ecosystem which eat other living creatures
There are herbivorres which eat plants and carnivores which eat other animals They are also
called phagotrops or macroconsumers
Reducers or Decomposers
Reducers decomposers saprotrophs or microconsumers are heterotrophic organisms that
breakdown dead and waste matter Fungi and certain bacteria are the prime representatives of
this category
Examples of ecosystemA classic example of an ecosystem is a small lake or pond The abiotic or non-living parts
of a fresh water pond include the water dissolved oxygen carbon dioxide inorganic salts such
as phosphates nitrates and chlorides of sodium potassium and calcium and a multitude of
organic compounds such as amino acids humic acids etc The living part of the freshwater pond
can be subdivided according to the functions of the organisms ie what they contribute toward
keeping the ecosystem operating as a stable interacting whole In a freshwater pond there are
two types of producers the larger plants growing along the shore or floating in shallow water
and the microscopic floating plants most of which are algae that are distributed throughout the
water as deep as light will penetrate These tiny plants collectively referred to as phytoplankton
are usually not visible unless they are present in great abundance and give the water a greenish
tinge
The macroconsumers or phagotrophs of pond ecosystems include insects and insect
larvae Crustacea fish and perhaps some freshwater clams Primary consumers such as
zooplankton found near the surface of water and benthos are the plant eaters and secondary
consumers are the carnivores that eat the primary consumers
Types of ecosystemEllenberg (1973) has classified the world into a hierarchy of ecosystems Biosphere is
the largest and all-encompassing ecosystem Next lower level is mega-ecosystem such as
marine ecosystems (ie ecosystems of saline water of sea ocean and lake) limnic ecosystems
(ie ecosystems of fresh-water) semi-terrestrial ecosystems (ieecosystems of wet soil and
air) terrestrisl ecosystems (ieecosystems of aerated soil and air) and urban-industrial
ecosystems (man-made ecosystems like cropland city etc) The next-lower level is represented
Insect Ecology and Population Dynamics
by macro-ecosystems ( forests etc) within the mega ndashecosystem Meso-ecosystems (eg a
cold deciduous broad leaf foreat with its fauna) are considered as the basic units of thus scheme
Meso-ecosystems are sub divided into micro-ecosystems which depart with respect to a certain
component( a low land mountain or sub-alpine cold deciduous broad leaf forest with its fauna)
Nano-ecosystems are further small ecosystems which are spatially contained within larger
ecosystems and that show a certain individuality of their own
PopulationAll living organisms exist in groups of the same species or populations The word
population (L populus people) was originally referred to a group of people occupying a
particular space Thus a population can be defined as the tptal assemblage of individuals of the
same species occupying a particular space at a given time
Dispersion
Populations have a tendency to disperse or spread out in all directions until some barrier
is reached Accordingly population dispersion is the movement of individuals into or out of the
population area It takes three forms emigration-one way outward movement immigration-
one way inward movement and migration-periodic departure and return
Dispersion supplements natality and mortality in shaping population growth form and
density and also it plays a significant role in the distribution of plants and animals even to the
areas previously unoccupied by the members of the population Most types of population
dispersion occur due to a number of reasons such as for obtaining food avoiding predators
preventing overcrowding result of action of wind and water environmental factors as light and
temperature breeding behavior physiological reasons as secretion of some hormone or for
interchange of genetic material between populations
Emigration
Emigration under natural conditions occurs when there is overcrowding in the migratory
locust This is generally regarded as an adaptive behaviour that regulates the population on a
particular site and prevents overexploitation of the habitat Further it leads to occupation of new
areas elsewhere By dispersing into new localities there is opportunity gained for interbreeding
with other populations leading to more genetic geterozygosity and adaptability
Immigration
Insect Ecology and Population Dynamics
Immigration leads to a rise in population level causing an overpopulation which may
lead to an increase beyond the carrying capasity These immigrations result in increased
mortality among the immigrants or decreased reproductive capasity of the individuals Both
emigration and immigration are initiated by weather and other abiotic and biotic environmental
factors
Migration
Migration is a peculiar kind of population dispersion which involves the mass movement
of entire population This can occur only in mobile organism and best developed in insects like
the butterfly Dannaus plexippus and in the migratory dragonflies Libellula quadrimaculata and
Pantala flavescens
In most cases migration of population may occur for food shelter or reproduction
Types
There are two types of ecosystems that are of ecological interest-open and cybernetic
Open systems depends on an outside environment to provide inputs and accept outputs
The ecosystem is an open system for it receives energy from an outside source the sun fixes and
utilizes it and ultimately dissipates heat to space If the suns energy were to be cut off the
ecosystem would cease to function An open system can consist of a number of components or
parts called subsystem and each subsystem can consist of a number of elements
A cybernetic system which can also be an open system has some sort of feedback
system to make it self ndashregulating Most living systems possess cybernetic systems that can
function at various levels from the cell to the community but always functioning through
organisms-the difference being that in living systems the set point is not fixed
What is ecology
The scientific study of the interactions that determine the distribution and abundance of organisms
scientific study - process of observation and experimentation leading to the rejection of all but one hypothesis not the truth or fact but the best fitting explanation of all the observations
interactions - include both biotic and abiotic factors
distribution - where insects occur
Insect Ecology and Population Dynamics
abundance - a measurement of population size
from the point of view of agriculture studies of populations of insects and their interactions with the environment are often restricted to a unit we call an agroecosystem
- agroecosystems
may be extensive corn belt or wheat growing areas of the Great Plains of North America or
limited - isolated orchard consisting of a few acres plantedwith widely-spaced trees or a greenhouse
- agroecosystems regardless of size have some common characteristics including
(1) created and maintained by human effort
(2) agroecosystems often lack temporal continuity
(3) plant selection by humans
(4) in any particular system often reduced species diversity frequently a single species dominates
(5) uniform phenology
phenology defn the study of seasonal changes which give rise to the observed periodicity of biological phenomena
(6) addition of nutrients
(7) frequently occurring insect weed and disease outbreaks
Ecology (from the Greek oikos meaning house or dwelling and logos meaning discourse) is the study of the interactions of organisms with each other and their environment Always remember that Ecology is a SCIENCE not a sociopolitical movement (eg environmentalism) The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystemsThe ECOSYSTEM is all living communities (biotic) and their associated non-living (abiotic) environmental components in a defined area Examples in southern Florida Everglades - a shallow wetland or marsh Hammock - hardwood (ie flowering tree) forest on higher ground within the Everglades Pine rocklands ndash on higher ground maintained by fire which prevents hardwoodsfrom taking overCoral ReefEstuaryMangrove
Insect Ecology and Population Dynamics
Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Conventionally ecology has been defined variously by different classical and modern
ecologists with different view of points Quite oddly no universally accepted definition of
ecology has been formulated by any ecologists so far and for the better understanding of scope
limitations purpose and mode of study of different ecological phenomena one has to go through
following chronologically arranged definitions of ecology
Ernst Haeckel (1869) defined ecology as the body of knowledge concerning the economy of
nature- the investigation of the total relations of animal to its inorganic and organic
environment
British ecologist Charles Elton (1927) defined ecology as the scientific natural history
concerned with the sociology and economics of animals
Taylor (1936) preferred to define ecology as the science of the relations of all organisms to all
their environments
A much broader definition of ecology of Allee et al (1949) considered ecology as the science
of inter-relation between living organisms and their environment including both the physical
and biotic environments and emphasizing inter-species as well as intra-species relations
SC Kendeigh (1961) defined ecology as the study of animals and plants in their relation to
each other and to their environment
Andrewartha (1961) defined ecology as the scientific study of the distribution and abundance
of animals
Odum (1963) defined ecology as the study of the structure and function of nature ecosystem
approach
GAPetrides (1968) defined ecology as the study of environmental interactions which control
the welfare of living things regulating their distribution abundance production and evolution
Krebs (1972) defined ecology as the scientific study of the interactions that determine the
distribution and abundance of organisms
Southwick (1976) defined ecology as the scientific study of the relationships of living
organisms with each other and with their environments He further elaborates his definition of
ecology by saying that it is the science of biological interactions among individuals
populations and communities and it is also the science of ecosystems-the inter-relations of
biotic communities with their non-living environments
Insect Ecology and Population Dynamics
Price (1984) defined ecology as the science of relationships of organisms to their environment
Insect ecology Insect ecology defined as the scientific study of the interactions (functional
process) that determine the distribution and abundance of true insects population in a specific
habitat
Objectives PurposesEcology is a distinct science because it is a body of knowledge not similarly organized in
any other division of biology because it uses s special set of techniques and procedures and
because it has a unique point of view The essence of ecology lies in the comprehensive
understanding of the meaning of following phenomena
1 The local and geographical distribution and abundance of organisms (habitat niche
community biogeography)
2 Temporal changes in the occurrence abundance and activities of organisms (seasonal
annual successional and geological)
3 The inter-relations between organisms in populations and their communities
(population ecology)
4 The structural adaptations and functional adjustments of organisms to their physical
environment (physiological ecology)
5 The behaviour of organisms under natural conditions (ethology)
6 The evolutionary development of all these inter-relations (evolutionary ecology)
7 The biological productivity of nature and its best use to mankind (ecosystem
ecology)
8 The conservation and management of natural resources (applied ecology)
Branches of ecologyEarly ecologists have recognized two major subdivisions of ecology in particular
reference to animal or to plants hence animal ecology and plant ecology But when it was
found that in the ecosystems plants and animals are very closely associated and inter-related
then both of these major ecological subdivisions became vague However when animals and
plants are given equal emphasis the term bioecology is used
Insect Ecology and Population Dynamics
Further ecology is often broadly divided into autecology and synecology Autecology
deals with the ecological study of one species of organism Thus an autecologist may study the
life history population dynamics behaviour home range and so on of a single species such as
the Maize-borer Chilo partellus Synecology deals with the ecological studies of communities or
entire ecosystems Thus a synecologist might study deserts or caves or tropical forests
Besides these major ecological subdivisions there are following specialized branches of ecology
1 Habitat ecology It deals with ecological study of different habitats on planet earth and
their effects on the organisms living
2 Organismal Ecology Evolutionary adaptations that enable individual organisms to
survive in their environment
3 Population Ecology Studies of the manner of growth density structure and regulation of
population of organisms and how members of a population coexists
4 Community Ecology Studies of the local distribution of animals in various habitats the
recognition and composition of community units and succession which indicate how
interactions between species (competition predation and symbiosis) affect community
structure and organization
5 Ecosystem Ecology Broadens to include the interactions of communities with all the
abiotic factors taken into consideration This branch of ecology often places research
emphasis upon energy flow and chemical cycling between living and non-living
components among and between communities
6 Biosphere Ecology The most complex level to study of ecology This is especially
a new field of study it has only recently become practical due to great advances
in satellite imagery of Earth global communication systems and breakdown of
national isolation which has allowed scientists from many countries to work
together and share results This is definitely he most interdisciplinary Ecological
Science it brings together scientific findings from many branches of science
including climatology oceanography meteorology soil science geology physics
chemistry and all the biological sciences
7 Evolutionary ecology It deals with the problems of niche segregation and speciation
8 Taxonomic ecology It is concerned with the ecology of different taxonomic groups of
living organisms and eventually includes following divisions of ecology microbial
Insect Ecology and Population Dynamics
ecology mammalian ecology insect ecology avian ecology parasitology human ecology
and so on
9 Applied ecology It deals with the application of ecological concepts to human need and
thus it includes following applications of ecology wild-life management range
management forestry conservation insect control epidemiology animal husbandry
aquaculture agriculture horticulture land use and pollution ecology
10 Production ecology It deals with the gross and net production of different
ecosystems like fresh water sea water agriculture horticulture etc and tries to do proper
management of these ecosystem so that maximum yield can be get from them
11 Physiological ecology The factors of environment have a direct bearing on the
functional aspects of organisms
12 Chemical ecology It concerns with the adaptations of animals of preferences of
particular organisms like insects to particular chemical substances
13 Space ecology It is a modern subdivision of ecology which is concerned with the
development of partially or completely regenerating ecosystems for supporting life of man
during long space flights or during extended exploration of extra-terrestrial environments
ScopeEcology is a multidisciplinary science and it includes not only the life sciences but
chemistry physics geology geography meteorology climatology hydrology palaeontology
archeology anthropology sociology and mathematics and statistics as well For explaining the
behaviour of an organism or biotic community in a given environment an ecologist has to
integrate the data which is obtained from many sources-morphology taxonomy genetics
physiology soil science climatology geology physics and chemistry
The scope of ecology is quite vast The study of ecological principles provides a
background for understanding the fundamental relationships of the natural community and also
the science dealing with particular environment such as forest soil ocean and inland waters
Many practical applications of this subject are found in agriculture horticulture forestry
limnology oceanography fishery biology biological survey pest control public
health toxicology pollution control conservation etc Ecological knowledge helps in
Insect Ecology and Population Dynamics
discovering new sources of food new unpolluting sources of energy and new methods of pest
control such as biological control which causes no environmental pollution
Some ecology related terminologyAbiotic factors Non-living ecological components of an ecosystem such water oxygen
sodium chloride nitrogen carbon dioxide etc and other physical and chemical influences such
as temperature light humidity pH etc
Biotic factors Living ecological components of an ecosystem such as producers
(chemosynthetic bacteria and photosynthetic green plants) consumers (heterotrophic animals
and decomposer organisms (bacteria fungi and other saprophytes)
Commensalism The living together of two species usually with benefit to one
Community A group of populations of plants and animals living together in a given place eg
the community of an oak forest a marsh a grassland a coral reef a desert etc
Competition Interaction occurs within interspecific or intraspecific population for utilizing
common resources that are in short supply (exploitation) or if the resources are not in short
supply for their survival or reproduction are known as competition
Consumers Organisms that ingest organic food (usually particulate) or other organisms
Dynamics In population ecology the study of reasons for changes in population size contrast
with statics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms
(biotic community) and non-living substances (abiotic environment) interacting to produce an
exchange of materials between the living and non-living parts
Habitat The natural abode of an organism including its total environment
Mutualism A interspecific relationship between two or more species in which both or all
benefit from the association and cannot live separately
Niche The ecological role or profession of an organism in its ecosystem its activities and
relationships to its community and total environment
Population Groups of individuals of single species a group of interacting individuals in a
definable space
Symbiosis The living together of two or more species
Insect Ecology and Population Dynamics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms (biotic
community) and non-living substances (abiotic environment) interacting to produce an exchange
of materials between the living and non-living parts It may be as small as a puddle or as large as
the entire earth Further an ecosystem may be natural as a pond a lake a river an estuary an
ocean a forest etc or it may be man-made or artificial like an aquarium a dam a cropland a
garden an orchard a city and so on The term ecosystem was coined by a Ag Tansley (1935)-
its eco part means environment and the system part implies a complex of coordinated units
Structure of an ecosystem
From structural point of view all ecosystems consists of following four basic
components
1 Abiotic Substances
2 Biotic Substances factors
a Producers
b Consumers
c Reducers or Decomposers
Biotic Substances
These include basic inorganic and organic compounds of the environment or habitat of
the organism The inorganic compounds of an ecosystem are carbon dioxide water nitrogen
calcium phosphate all of which are involved in matter cycles The organic compounds of an
ecosystem are proteins carbohydrates lipids and amino acids all of which are synthesized by
the biota of an ecosystem and are reached to ecosystem as their wastes dead remains etc The
climate temperature light soil etc are other abiotic components of the ecosystem
Producers
Producers are autotrophic organisms like chemosynthetic and photosynthetic bacteria
blue green algae algae and all other green plants They are called ecosystem producers because
they capture energy from non-organic sources especially light and store some of the energy in
the form of chemical bonds for the later use
Insect Ecology and Population Dynamics
Consumers
They are heterotrophic organisms in the ecosystem which eat other living creatures
There are herbivorres which eat plants and carnivores which eat other animals They are also
called phagotrops or macroconsumers
Reducers or Decomposers
Reducers decomposers saprotrophs or microconsumers are heterotrophic organisms that
breakdown dead and waste matter Fungi and certain bacteria are the prime representatives of
this category
Examples of ecosystemA classic example of an ecosystem is a small lake or pond The abiotic or non-living parts
of a fresh water pond include the water dissolved oxygen carbon dioxide inorganic salts such
as phosphates nitrates and chlorides of sodium potassium and calcium and a multitude of
organic compounds such as amino acids humic acids etc The living part of the freshwater pond
can be subdivided according to the functions of the organisms ie what they contribute toward
keeping the ecosystem operating as a stable interacting whole In a freshwater pond there are
two types of producers the larger plants growing along the shore or floating in shallow water
and the microscopic floating plants most of which are algae that are distributed throughout the
water as deep as light will penetrate These tiny plants collectively referred to as phytoplankton
are usually not visible unless they are present in great abundance and give the water a greenish
tinge
The macroconsumers or phagotrophs of pond ecosystems include insects and insect
larvae Crustacea fish and perhaps some freshwater clams Primary consumers such as
zooplankton found near the surface of water and benthos are the plant eaters and secondary
consumers are the carnivores that eat the primary consumers
Types of ecosystemEllenberg (1973) has classified the world into a hierarchy of ecosystems Biosphere is
the largest and all-encompassing ecosystem Next lower level is mega-ecosystem such as
marine ecosystems (ie ecosystems of saline water of sea ocean and lake) limnic ecosystems
(ie ecosystems of fresh-water) semi-terrestrial ecosystems (ieecosystems of wet soil and
air) terrestrisl ecosystems (ieecosystems of aerated soil and air) and urban-industrial
ecosystems (man-made ecosystems like cropland city etc) The next-lower level is represented
Insect Ecology and Population Dynamics
by macro-ecosystems ( forests etc) within the mega ndashecosystem Meso-ecosystems (eg a
cold deciduous broad leaf foreat with its fauna) are considered as the basic units of thus scheme
Meso-ecosystems are sub divided into micro-ecosystems which depart with respect to a certain
component( a low land mountain or sub-alpine cold deciduous broad leaf forest with its fauna)
Nano-ecosystems are further small ecosystems which are spatially contained within larger
ecosystems and that show a certain individuality of their own
PopulationAll living organisms exist in groups of the same species or populations The word
population (L populus people) was originally referred to a group of people occupying a
particular space Thus a population can be defined as the tptal assemblage of individuals of the
same species occupying a particular space at a given time
Dispersion
Populations have a tendency to disperse or spread out in all directions until some barrier
is reached Accordingly population dispersion is the movement of individuals into or out of the
population area It takes three forms emigration-one way outward movement immigration-
one way inward movement and migration-periodic departure and return
Dispersion supplements natality and mortality in shaping population growth form and
density and also it plays a significant role in the distribution of plants and animals even to the
areas previously unoccupied by the members of the population Most types of population
dispersion occur due to a number of reasons such as for obtaining food avoiding predators
preventing overcrowding result of action of wind and water environmental factors as light and
temperature breeding behavior physiological reasons as secretion of some hormone or for
interchange of genetic material between populations
Emigration
Emigration under natural conditions occurs when there is overcrowding in the migratory
locust This is generally regarded as an adaptive behaviour that regulates the population on a
particular site and prevents overexploitation of the habitat Further it leads to occupation of new
areas elsewhere By dispersing into new localities there is opportunity gained for interbreeding
with other populations leading to more genetic geterozygosity and adaptability
Immigration
Insect Ecology and Population Dynamics
Immigration leads to a rise in population level causing an overpopulation which may
lead to an increase beyond the carrying capasity These immigrations result in increased
mortality among the immigrants or decreased reproductive capasity of the individuals Both
emigration and immigration are initiated by weather and other abiotic and biotic environmental
factors
Migration
Migration is a peculiar kind of population dispersion which involves the mass movement
of entire population This can occur only in mobile organism and best developed in insects like
the butterfly Dannaus plexippus and in the migratory dragonflies Libellula quadrimaculata and
Pantala flavescens
In most cases migration of population may occur for food shelter or reproduction
Types
There are two types of ecosystems that are of ecological interest-open and cybernetic
Open systems depends on an outside environment to provide inputs and accept outputs
The ecosystem is an open system for it receives energy from an outside source the sun fixes and
utilizes it and ultimately dissipates heat to space If the suns energy were to be cut off the
ecosystem would cease to function An open system can consist of a number of components or
parts called subsystem and each subsystem can consist of a number of elements
A cybernetic system which can also be an open system has some sort of feedback
system to make it self ndashregulating Most living systems possess cybernetic systems that can
function at various levels from the cell to the community but always functioning through
organisms-the difference being that in living systems the set point is not fixed
What is ecology
The scientific study of the interactions that determine the distribution and abundance of organisms
scientific study - process of observation and experimentation leading to the rejection of all but one hypothesis not the truth or fact but the best fitting explanation of all the observations
interactions - include both biotic and abiotic factors
distribution - where insects occur
Insect Ecology and Population Dynamics
abundance - a measurement of population size
from the point of view of agriculture studies of populations of insects and their interactions with the environment are often restricted to a unit we call an agroecosystem
- agroecosystems
may be extensive corn belt or wheat growing areas of the Great Plains of North America or
limited - isolated orchard consisting of a few acres plantedwith widely-spaced trees or a greenhouse
- agroecosystems regardless of size have some common characteristics including
(1) created and maintained by human effort
(2) agroecosystems often lack temporal continuity
(3) plant selection by humans
(4) in any particular system often reduced species diversity frequently a single species dominates
(5) uniform phenology
phenology defn the study of seasonal changes which give rise to the observed periodicity of biological phenomena
(6) addition of nutrients
(7) frequently occurring insect weed and disease outbreaks
Ecology (from the Greek oikos meaning house or dwelling and logos meaning discourse) is the study of the interactions of organisms with each other and their environment Always remember that Ecology is a SCIENCE not a sociopolitical movement (eg environmentalism) The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystemsThe ECOSYSTEM is all living communities (biotic) and their associated non-living (abiotic) environmental components in a defined area Examples in southern Florida Everglades - a shallow wetland or marsh Hammock - hardwood (ie flowering tree) forest on higher ground within the Everglades Pine rocklands ndash on higher ground maintained by fire which prevents hardwoodsfrom taking overCoral ReefEstuaryMangrove
Insect Ecology and Population Dynamics
Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Price (1984) defined ecology as the science of relationships of organisms to their environment
Insect ecology Insect ecology defined as the scientific study of the interactions (functional
process) that determine the distribution and abundance of true insects population in a specific
habitat
Objectives PurposesEcology is a distinct science because it is a body of knowledge not similarly organized in
any other division of biology because it uses s special set of techniques and procedures and
because it has a unique point of view The essence of ecology lies in the comprehensive
understanding of the meaning of following phenomena
1 The local and geographical distribution and abundance of organisms (habitat niche
community biogeography)
2 Temporal changes in the occurrence abundance and activities of organisms (seasonal
annual successional and geological)
3 The inter-relations between organisms in populations and their communities
(population ecology)
4 The structural adaptations and functional adjustments of organisms to their physical
environment (physiological ecology)
5 The behaviour of organisms under natural conditions (ethology)
6 The evolutionary development of all these inter-relations (evolutionary ecology)
7 The biological productivity of nature and its best use to mankind (ecosystem
ecology)
8 The conservation and management of natural resources (applied ecology)
Branches of ecologyEarly ecologists have recognized two major subdivisions of ecology in particular
reference to animal or to plants hence animal ecology and plant ecology But when it was
found that in the ecosystems plants and animals are very closely associated and inter-related
then both of these major ecological subdivisions became vague However when animals and
plants are given equal emphasis the term bioecology is used
Insect Ecology and Population Dynamics
Further ecology is often broadly divided into autecology and synecology Autecology
deals with the ecological study of one species of organism Thus an autecologist may study the
life history population dynamics behaviour home range and so on of a single species such as
the Maize-borer Chilo partellus Synecology deals with the ecological studies of communities or
entire ecosystems Thus a synecologist might study deserts or caves or tropical forests
Besides these major ecological subdivisions there are following specialized branches of ecology
1 Habitat ecology It deals with ecological study of different habitats on planet earth and
their effects on the organisms living
2 Organismal Ecology Evolutionary adaptations that enable individual organisms to
survive in their environment
3 Population Ecology Studies of the manner of growth density structure and regulation of
population of organisms and how members of a population coexists
4 Community Ecology Studies of the local distribution of animals in various habitats the
recognition and composition of community units and succession which indicate how
interactions between species (competition predation and symbiosis) affect community
structure and organization
5 Ecosystem Ecology Broadens to include the interactions of communities with all the
abiotic factors taken into consideration This branch of ecology often places research
emphasis upon energy flow and chemical cycling between living and non-living
components among and between communities
6 Biosphere Ecology The most complex level to study of ecology This is especially
a new field of study it has only recently become practical due to great advances
in satellite imagery of Earth global communication systems and breakdown of
national isolation which has allowed scientists from many countries to work
together and share results This is definitely he most interdisciplinary Ecological
Science it brings together scientific findings from many branches of science
including climatology oceanography meteorology soil science geology physics
chemistry and all the biological sciences
7 Evolutionary ecology It deals with the problems of niche segregation and speciation
8 Taxonomic ecology It is concerned with the ecology of different taxonomic groups of
living organisms and eventually includes following divisions of ecology microbial
Insect Ecology and Population Dynamics
ecology mammalian ecology insect ecology avian ecology parasitology human ecology
and so on
9 Applied ecology It deals with the application of ecological concepts to human need and
thus it includes following applications of ecology wild-life management range
management forestry conservation insect control epidemiology animal husbandry
aquaculture agriculture horticulture land use and pollution ecology
10 Production ecology It deals with the gross and net production of different
ecosystems like fresh water sea water agriculture horticulture etc and tries to do proper
management of these ecosystem so that maximum yield can be get from them
11 Physiological ecology The factors of environment have a direct bearing on the
functional aspects of organisms
12 Chemical ecology It concerns with the adaptations of animals of preferences of
particular organisms like insects to particular chemical substances
13 Space ecology It is a modern subdivision of ecology which is concerned with the
development of partially or completely regenerating ecosystems for supporting life of man
during long space flights or during extended exploration of extra-terrestrial environments
ScopeEcology is a multidisciplinary science and it includes not only the life sciences but
chemistry physics geology geography meteorology climatology hydrology palaeontology
archeology anthropology sociology and mathematics and statistics as well For explaining the
behaviour of an organism or biotic community in a given environment an ecologist has to
integrate the data which is obtained from many sources-morphology taxonomy genetics
physiology soil science climatology geology physics and chemistry
The scope of ecology is quite vast The study of ecological principles provides a
background for understanding the fundamental relationships of the natural community and also
the science dealing with particular environment such as forest soil ocean and inland waters
Many practical applications of this subject are found in agriculture horticulture forestry
limnology oceanography fishery biology biological survey pest control public
health toxicology pollution control conservation etc Ecological knowledge helps in
Insect Ecology and Population Dynamics
discovering new sources of food new unpolluting sources of energy and new methods of pest
control such as biological control which causes no environmental pollution
Some ecology related terminologyAbiotic factors Non-living ecological components of an ecosystem such water oxygen
sodium chloride nitrogen carbon dioxide etc and other physical and chemical influences such
as temperature light humidity pH etc
Biotic factors Living ecological components of an ecosystem such as producers
(chemosynthetic bacteria and photosynthetic green plants) consumers (heterotrophic animals
and decomposer organisms (bacteria fungi and other saprophytes)
Commensalism The living together of two species usually with benefit to one
Community A group of populations of plants and animals living together in a given place eg
the community of an oak forest a marsh a grassland a coral reef a desert etc
Competition Interaction occurs within interspecific or intraspecific population for utilizing
common resources that are in short supply (exploitation) or if the resources are not in short
supply for their survival or reproduction are known as competition
Consumers Organisms that ingest organic food (usually particulate) or other organisms
Dynamics In population ecology the study of reasons for changes in population size contrast
with statics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms
(biotic community) and non-living substances (abiotic environment) interacting to produce an
exchange of materials between the living and non-living parts
Habitat The natural abode of an organism including its total environment
Mutualism A interspecific relationship between two or more species in which both or all
benefit from the association and cannot live separately
Niche The ecological role or profession of an organism in its ecosystem its activities and
relationships to its community and total environment
Population Groups of individuals of single species a group of interacting individuals in a
definable space
Symbiosis The living together of two or more species
Insect Ecology and Population Dynamics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms (biotic
community) and non-living substances (abiotic environment) interacting to produce an exchange
of materials between the living and non-living parts It may be as small as a puddle or as large as
the entire earth Further an ecosystem may be natural as a pond a lake a river an estuary an
ocean a forest etc or it may be man-made or artificial like an aquarium a dam a cropland a
garden an orchard a city and so on The term ecosystem was coined by a Ag Tansley (1935)-
its eco part means environment and the system part implies a complex of coordinated units
Structure of an ecosystem
From structural point of view all ecosystems consists of following four basic
components
1 Abiotic Substances
2 Biotic Substances factors
a Producers
b Consumers
c Reducers or Decomposers
Biotic Substances
These include basic inorganic and organic compounds of the environment or habitat of
the organism The inorganic compounds of an ecosystem are carbon dioxide water nitrogen
calcium phosphate all of which are involved in matter cycles The organic compounds of an
ecosystem are proteins carbohydrates lipids and amino acids all of which are synthesized by
the biota of an ecosystem and are reached to ecosystem as their wastes dead remains etc The
climate temperature light soil etc are other abiotic components of the ecosystem
Producers
Producers are autotrophic organisms like chemosynthetic and photosynthetic bacteria
blue green algae algae and all other green plants They are called ecosystem producers because
they capture energy from non-organic sources especially light and store some of the energy in
the form of chemical bonds for the later use
Insect Ecology and Population Dynamics
Consumers
They are heterotrophic organisms in the ecosystem which eat other living creatures
There are herbivorres which eat plants and carnivores which eat other animals They are also
called phagotrops or macroconsumers
Reducers or Decomposers
Reducers decomposers saprotrophs or microconsumers are heterotrophic organisms that
breakdown dead and waste matter Fungi and certain bacteria are the prime representatives of
this category
Examples of ecosystemA classic example of an ecosystem is a small lake or pond The abiotic or non-living parts
of a fresh water pond include the water dissolved oxygen carbon dioxide inorganic salts such
as phosphates nitrates and chlorides of sodium potassium and calcium and a multitude of
organic compounds such as amino acids humic acids etc The living part of the freshwater pond
can be subdivided according to the functions of the organisms ie what they contribute toward
keeping the ecosystem operating as a stable interacting whole In a freshwater pond there are
two types of producers the larger plants growing along the shore or floating in shallow water
and the microscopic floating plants most of which are algae that are distributed throughout the
water as deep as light will penetrate These tiny plants collectively referred to as phytoplankton
are usually not visible unless they are present in great abundance and give the water a greenish
tinge
The macroconsumers or phagotrophs of pond ecosystems include insects and insect
larvae Crustacea fish and perhaps some freshwater clams Primary consumers such as
zooplankton found near the surface of water and benthos are the plant eaters and secondary
consumers are the carnivores that eat the primary consumers
Types of ecosystemEllenberg (1973) has classified the world into a hierarchy of ecosystems Biosphere is
the largest and all-encompassing ecosystem Next lower level is mega-ecosystem such as
marine ecosystems (ie ecosystems of saline water of sea ocean and lake) limnic ecosystems
(ie ecosystems of fresh-water) semi-terrestrial ecosystems (ieecosystems of wet soil and
air) terrestrisl ecosystems (ieecosystems of aerated soil and air) and urban-industrial
ecosystems (man-made ecosystems like cropland city etc) The next-lower level is represented
Insect Ecology and Population Dynamics
by macro-ecosystems ( forests etc) within the mega ndashecosystem Meso-ecosystems (eg a
cold deciduous broad leaf foreat with its fauna) are considered as the basic units of thus scheme
Meso-ecosystems are sub divided into micro-ecosystems which depart with respect to a certain
component( a low land mountain or sub-alpine cold deciduous broad leaf forest with its fauna)
Nano-ecosystems are further small ecosystems which are spatially contained within larger
ecosystems and that show a certain individuality of their own
PopulationAll living organisms exist in groups of the same species or populations The word
population (L populus people) was originally referred to a group of people occupying a
particular space Thus a population can be defined as the tptal assemblage of individuals of the
same species occupying a particular space at a given time
Dispersion
Populations have a tendency to disperse or spread out in all directions until some barrier
is reached Accordingly population dispersion is the movement of individuals into or out of the
population area It takes three forms emigration-one way outward movement immigration-
one way inward movement and migration-periodic departure and return
Dispersion supplements natality and mortality in shaping population growth form and
density and also it plays a significant role in the distribution of plants and animals even to the
areas previously unoccupied by the members of the population Most types of population
dispersion occur due to a number of reasons such as for obtaining food avoiding predators
preventing overcrowding result of action of wind and water environmental factors as light and
temperature breeding behavior physiological reasons as secretion of some hormone or for
interchange of genetic material between populations
Emigration
Emigration under natural conditions occurs when there is overcrowding in the migratory
locust This is generally regarded as an adaptive behaviour that regulates the population on a
particular site and prevents overexploitation of the habitat Further it leads to occupation of new
areas elsewhere By dispersing into new localities there is opportunity gained for interbreeding
with other populations leading to more genetic geterozygosity and adaptability
Immigration
Insect Ecology and Population Dynamics
Immigration leads to a rise in population level causing an overpopulation which may
lead to an increase beyond the carrying capasity These immigrations result in increased
mortality among the immigrants or decreased reproductive capasity of the individuals Both
emigration and immigration are initiated by weather and other abiotic and biotic environmental
factors
Migration
Migration is a peculiar kind of population dispersion which involves the mass movement
of entire population This can occur only in mobile organism and best developed in insects like
the butterfly Dannaus plexippus and in the migratory dragonflies Libellula quadrimaculata and
Pantala flavescens
In most cases migration of population may occur for food shelter or reproduction
Types
There are two types of ecosystems that are of ecological interest-open and cybernetic
Open systems depends on an outside environment to provide inputs and accept outputs
The ecosystem is an open system for it receives energy from an outside source the sun fixes and
utilizes it and ultimately dissipates heat to space If the suns energy were to be cut off the
ecosystem would cease to function An open system can consist of a number of components or
parts called subsystem and each subsystem can consist of a number of elements
A cybernetic system which can also be an open system has some sort of feedback
system to make it self ndashregulating Most living systems possess cybernetic systems that can
function at various levels from the cell to the community but always functioning through
organisms-the difference being that in living systems the set point is not fixed
What is ecology
The scientific study of the interactions that determine the distribution and abundance of organisms
scientific study - process of observation and experimentation leading to the rejection of all but one hypothesis not the truth or fact but the best fitting explanation of all the observations
interactions - include both biotic and abiotic factors
distribution - where insects occur
Insect Ecology and Population Dynamics
abundance - a measurement of population size
from the point of view of agriculture studies of populations of insects and their interactions with the environment are often restricted to a unit we call an agroecosystem
- agroecosystems
may be extensive corn belt or wheat growing areas of the Great Plains of North America or
limited - isolated orchard consisting of a few acres plantedwith widely-spaced trees or a greenhouse
- agroecosystems regardless of size have some common characteristics including
(1) created and maintained by human effort
(2) agroecosystems often lack temporal continuity
(3) plant selection by humans
(4) in any particular system often reduced species diversity frequently a single species dominates
(5) uniform phenology
phenology defn the study of seasonal changes which give rise to the observed periodicity of biological phenomena
(6) addition of nutrients
(7) frequently occurring insect weed and disease outbreaks
Ecology (from the Greek oikos meaning house or dwelling and logos meaning discourse) is the study of the interactions of organisms with each other and their environment Always remember that Ecology is a SCIENCE not a sociopolitical movement (eg environmentalism) The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystemsThe ECOSYSTEM is all living communities (biotic) and their associated non-living (abiotic) environmental components in a defined area Examples in southern Florida Everglades - a shallow wetland or marsh Hammock - hardwood (ie flowering tree) forest on higher ground within the Everglades Pine rocklands ndash on higher ground maintained by fire which prevents hardwoodsfrom taking overCoral ReefEstuaryMangrove
Insect Ecology and Population Dynamics
Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Further ecology is often broadly divided into autecology and synecology Autecology
deals with the ecological study of one species of organism Thus an autecologist may study the
life history population dynamics behaviour home range and so on of a single species such as
the Maize-borer Chilo partellus Synecology deals with the ecological studies of communities or
entire ecosystems Thus a synecologist might study deserts or caves or tropical forests
Besides these major ecological subdivisions there are following specialized branches of ecology
1 Habitat ecology It deals with ecological study of different habitats on planet earth and
their effects on the organisms living
2 Organismal Ecology Evolutionary adaptations that enable individual organisms to
survive in their environment
3 Population Ecology Studies of the manner of growth density structure and regulation of
population of organisms and how members of a population coexists
4 Community Ecology Studies of the local distribution of animals in various habitats the
recognition and composition of community units and succession which indicate how
interactions between species (competition predation and symbiosis) affect community
structure and organization
5 Ecosystem Ecology Broadens to include the interactions of communities with all the
abiotic factors taken into consideration This branch of ecology often places research
emphasis upon energy flow and chemical cycling between living and non-living
components among and between communities
6 Biosphere Ecology The most complex level to study of ecology This is especially
a new field of study it has only recently become practical due to great advances
in satellite imagery of Earth global communication systems and breakdown of
national isolation which has allowed scientists from many countries to work
together and share results This is definitely he most interdisciplinary Ecological
Science it brings together scientific findings from many branches of science
including climatology oceanography meteorology soil science geology physics
chemistry and all the biological sciences
7 Evolutionary ecology It deals with the problems of niche segregation and speciation
8 Taxonomic ecology It is concerned with the ecology of different taxonomic groups of
living organisms and eventually includes following divisions of ecology microbial
Insect Ecology and Population Dynamics
ecology mammalian ecology insect ecology avian ecology parasitology human ecology
and so on
9 Applied ecology It deals with the application of ecological concepts to human need and
thus it includes following applications of ecology wild-life management range
management forestry conservation insect control epidemiology animal husbandry
aquaculture agriculture horticulture land use and pollution ecology
10 Production ecology It deals with the gross and net production of different
ecosystems like fresh water sea water agriculture horticulture etc and tries to do proper
management of these ecosystem so that maximum yield can be get from them
11 Physiological ecology The factors of environment have a direct bearing on the
functional aspects of organisms
12 Chemical ecology It concerns with the adaptations of animals of preferences of
particular organisms like insects to particular chemical substances
13 Space ecology It is a modern subdivision of ecology which is concerned with the
development of partially or completely regenerating ecosystems for supporting life of man
during long space flights or during extended exploration of extra-terrestrial environments
ScopeEcology is a multidisciplinary science and it includes not only the life sciences but
chemistry physics geology geography meteorology climatology hydrology palaeontology
archeology anthropology sociology and mathematics and statistics as well For explaining the
behaviour of an organism or biotic community in a given environment an ecologist has to
integrate the data which is obtained from many sources-morphology taxonomy genetics
physiology soil science climatology geology physics and chemistry
The scope of ecology is quite vast The study of ecological principles provides a
background for understanding the fundamental relationships of the natural community and also
the science dealing with particular environment such as forest soil ocean and inland waters
Many practical applications of this subject are found in agriculture horticulture forestry
limnology oceanography fishery biology biological survey pest control public
health toxicology pollution control conservation etc Ecological knowledge helps in
Insect Ecology and Population Dynamics
discovering new sources of food new unpolluting sources of energy and new methods of pest
control such as biological control which causes no environmental pollution
Some ecology related terminologyAbiotic factors Non-living ecological components of an ecosystem such water oxygen
sodium chloride nitrogen carbon dioxide etc and other physical and chemical influences such
as temperature light humidity pH etc
Biotic factors Living ecological components of an ecosystem such as producers
(chemosynthetic bacteria and photosynthetic green plants) consumers (heterotrophic animals
and decomposer organisms (bacteria fungi and other saprophytes)
Commensalism The living together of two species usually with benefit to one
Community A group of populations of plants and animals living together in a given place eg
the community of an oak forest a marsh a grassland a coral reef a desert etc
Competition Interaction occurs within interspecific or intraspecific population for utilizing
common resources that are in short supply (exploitation) or if the resources are not in short
supply for their survival or reproduction are known as competition
Consumers Organisms that ingest organic food (usually particulate) or other organisms
Dynamics In population ecology the study of reasons for changes in population size contrast
with statics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms
(biotic community) and non-living substances (abiotic environment) interacting to produce an
exchange of materials between the living and non-living parts
Habitat The natural abode of an organism including its total environment
Mutualism A interspecific relationship between two or more species in which both or all
benefit from the association and cannot live separately
Niche The ecological role or profession of an organism in its ecosystem its activities and
relationships to its community and total environment
Population Groups of individuals of single species a group of interacting individuals in a
definable space
Symbiosis The living together of two or more species
Insect Ecology and Population Dynamics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms (biotic
community) and non-living substances (abiotic environment) interacting to produce an exchange
of materials between the living and non-living parts It may be as small as a puddle or as large as
the entire earth Further an ecosystem may be natural as a pond a lake a river an estuary an
ocean a forest etc or it may be man-made or artificial like an aquarium a dam a cropland a
garden an orchard a city and so on The term ecosystem was coined by a Ag Tansley (1935)-
its eco part means environment and the system part implies a complex of coordinated units
Structure of an ecosystem
From structural point of view all ecosystems consists of following four basic
components
1 Abiotic Substances
2 Biotic Substances factors
a Producers
b Consumers
c Reducers or Decomposers
Biotic Substances
These include basic inorganic and organic compounds of the environment or habitat of
the organism The inorganic compounds of an ecosystem are carbon dioxide water nitrogen
calcium phosphate all of which are involved in matter cycles The organic compounds of an
ecosystem are proteins carbohydrates lipids and amino acids all of which are synthesized by
the biota of an ecosystem and are reached to ecosystem as their wastes dead remains etc The
climate temperature light soil etc are other abiotic components of the ecosystem
Producers
Producers are autotrophic organisms like chemosynthetic and photosynthetic bacteria
blue green algae algae and all other green plants They are called ecosystem producers because
they capture energy from non-organic sources especially light and store some of the energy in
the form of chemical bonds for the later use
Insect Ecology and Population Dynamics
Consumers
They are heterotrophic organisms in the ecosystem which eat other living creatures
There are herbivorres which eat plants and carnivores which eat other animals They are also
called phagotrops or macroconsumers
Reducers or Decomposers
Reducers decomposers saprotrophs or microconsumers are heterotrophic organisms that
breakdown dead and waste matter Fungi and certain bacteria are the prime representatives of
this category
Examples of ecosystemA classic example of an ecosystem is a small lake or pond The abiotic or non-living parts
of a fresh water pond include the water dissolved oxygen carbon dioxide inorganic salts such
as phosphates nitrates and chlorides of sodium potassium and calcium and a multitude of
organic compounds such as amino acids humic acids etc The living part of the freshwater pond
can be subdivided according to the functions of the organisms ie what they contribute toward
keeping the ecosystem operating as a stable interacting whole In a freshwater pond there are
two types of producers the larger plants growing along the shore or floating in shallow water
and the microscopic floating plants most of which are algae that are distributed throughout the
water as deep as light will penetrate These tiny plants collectively referred to as phytoplankton
are usually not visible unless they are present in great abundance and give the water a greenish
tinge
The macroconsumers or phagotrophs of pond ecosystems include insects and insect
larvae Crustacea fish and perhaps some freshwater clams Primary consumers such as
zooplankton found near the surface of water and benthos are the plant eaters and secondary
consumers are the carnivores that eat the primary consumers
Types of ecosystemEllenberg (1973) has classified the world into a hierarchy of ecosystems Biosphere is
the largest and all-encompassing ecosystem Next lower level is mega-ecosystem such as
marine ecosystems (ie ecosystems of saline water of sea ocean and lake) limnic ecosystems
(ie ecosystems of fresh-water) semi-terrestrial ecosystems (ieecosystems of wet soil and
air) terrestrisl ecosystems (ieecosystems of aerated soil and air) and urban-industrial
ecosystems (man-made ecosystems like cropland city etc) The next-lower level is represented
Insect Ecology and Population Dynamics
by macro-ecosystems ( forests etc) within the mega ndashecosystem Meso-ecosystems (eg a
cold deciduous broad leaf foreat with its fauna) are considered as the basic units of thus scheme
Meso-ecosystems are sub divided into micro-ecosystems which depart with respect to a certain
component( a low land mountain or sub-alpine cold deciduous broad leaf forest with its fauna)
Nano-ecosystems are further small ecosystems which are spatially contained within larger
ecosystems and that show a certain individuality of their own
PopulationAll living organisms exist in groups of the same species or populations The word
population (L populus people) was originally referred to a group of people occupying a
particular space Thus a population can be defined as the tptal assemblage of individuals of the
same species occupying a particular space at a given time
Dispersion
Populations have a tendency to disperse or spread out in all directions until some barrier
is reached Accordingly population dispersion is the movement of individuals into or out of the
population area It takes three forms emigration-one way outward movement immigration-
one way inward movement and migration-periodic departure and return
Dispersion supplements natality and mortality in shaping population growth form and
density and also it plays a significant role in the distribution of plants and animals even to the
areas previously unoccupied by the members of the population Most types of population
dispersion occur due to a number of reasons such as for obtaining food avoiding predators
preventing overcrowding result of action of wind and water environmental factors as light and
temperature breeding behavior physiological reasons as secretion of some hormone or for
interchange of genetic material between populations
Emigration
Emigration under natural conditions occurs when there is overcrowding in the migratory
locust This is generally regarded as an adaptive behaviour that regulates the population on a
particular site and prevents overexploitation of the habitat Further it leads to occupation of new
areas elsewhere By dispersing into new localities there is opportunity gained for interbreeding
with other populations leading to more genetic geterozygosity and adaptability
Immigration
Insect Ecology and Population Dynamics
Immigration leads to a rise in population level causing an overpopulation which may
lead to an increase beyond the carrying capasity These immigrations result in increased
mortality among the immigrants or decreased reproductive capasity of the individuals Both
emigration and immigration are initiated by weather and other abiotic and biotic environmental
factors
Migration
Migration is a peculiar kind of population dispersion which involves the mass movement
of entire population This can occur only in mobile organism and best developed in insects like
the butterfly Dannaus plexippus and in the migratory dragonflies Libellula quadrimaculata and
Pantala flavescens
In most cases migration of population may occur for food shelter or reproduction
Types
There are two types of ecosystems that are of ecological interest-open and cybernetic
Open systems depends on an outside environment to provide inputs and accept outputs
The ecosystem is an open system for it receives energy from an outside source the sun fixes and
utilizes it and ultimately dissipates heat to space If the suns energy were to be cut off the
ecosystem would cease to function An open system can consist of a number of components or
parts called subsystem and each subsystem can consist of a number of elements
A cybernetic system which can also be an open system has some sort of feedback
system to make it self ndashregulating Most living systems possess cybernetic systems that can
function at various levels from the cell to the community but always functioning through
organisms-the difference being that in living systems the set point is not fixed
What is ecology
The scientific study of the interactions that determine the distribution and abundance of organisms
scientific study - process of observation and experimentation leading to the rejection of all but one hypothesis not the truth or fact but the best fitting explanation of all the observations
interactions - include both biotic and abiotic factors
distribution - where insects occur
Insect Ecology and Population Dynamics
abundance - a measurement of population size
from the point of view of agriculture studies of populations of insects and their interactions with the environment are often restricted to a unit we call an agroecosystem
- agroecosystems
may be extensive corn belt or wheat growing areas of the Great Plains of North America or
limited - isolated orchard consisting of a few acres plantedwith widely-spaced trees or a greenhouse
- agroecosystems regardless of size have some common characteristics including
(1) created and maintained by human effort
(2) agroecosystems often lack temporal continuity
(3) plant selection by humans
(4) in any particular system often reduced species diversity frequently a single species dominates
(5) uniform phenology
phenology defn the study of seasonal changes which give rise to the observed periodicity of biological phenomena
(6) addition of nutrients
(7) frequently occurring insect weed and disease outbreaks
Ecology (from the Greek oikos meaning house or dwelling and logos meaning discourse) is the study of the interactions of organisms with each other and their environment Always remember that Ecology is a SCIENCE not a sociopolitical movement (eg environmentalism) The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystemsThe ECOSYSTEM is all living communities (biotic) and their associated non-living (abiotic) environmental components in a defined area Examples in southern Florida Everglades - a shallow wetland or marsh Hammock - hardwood (ie flowering tree) forest on higher ground within the Everglades Pine rocklands ndash on higher ground maintained by fire which prevents hardwoodsfrom taking overCoral ReefEstuaryMangrove
Insect Ecology and Population Dynamics
Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
ecology mammalian ecology insect ecology avian ecology parasitology human ecology
and so on
9 Applied ecology It deals with the application of ecological concepts to human need and
thus it includes following applications of ecology wild-life management range
management forestry conservation insect control epidemiology animal husbandry
aquaculture agriculture horticulture land use and pollution ecology
10 Production ecology It deals with the gross and net production of different
ecosystems like fresh water sea water agriculture horticulture etc and tries to do proper
management of these ecosystem so that maximum yield can be get from them
11 Physiological ecology The factors of environment have a direct bearing on the
functional aspects of organisms
12 Chemical ecology It concerns with the adaptations of animals of preferences of
particular organisms like insects to particular chemical substances
13 Space ecology It is a modern subdivision of ecology which is concerned with the
development of partially or completely regenerating ecosystems for supporting life of man
during long space flights or during extended exploration of extra-terrestrial environments
ScopeEcology is a multidisciplinary science and it includes not only the life sciences but
chemistry physics geology geography meteorology climatology hydrology palaeontology
archeology anthropology sociology and mathematics and statistics as well For explaining the
behaviour of an organism or biotic community in a given environment an ecologist has to
integrate the data which is obtained from many sources-morphology taxonomy genetics
physiology soil science climatology geology physics and chemistry
The scope of ecology is quite vast The study of ecological principles provides a
background for understanding the fundamental relationships of the natural community and also
the science dealing with particular environment such as forest soil ocean and inland waters
Many practical applications of this subject are found in agriculture horticulture forestry
limnology oceanography fishery biology biological survey pest control public
health toxicology pollution control conservation etc Ecological knowledge helps in
Insect Ecology and Population Dynamics
discovering new sources of food new unpolluting sources of energy and new methods of pest
control such as biological control which causes no environmental pollution
Some ecology related terminologyAbiotic factors Non-living ecological components of an ecosystem such water oxygen
sodium chloride nitrogen carbon dioxide etc and other physical and chemical influences such
as temperature light humidity pH etc
Biotic factors Living ecological components of an ecosystem such as producers
(chemosynthetic bacteria and photosynthetic green plants) consumers (heterotrophic animals
and decomposer organisms (bacteria fungi and other saprophytes)
Commensalism The living together of two species usually with benefit to one
Community A group of populations of plants and animals living together in a given place eg
the community of an oak forest a marsh a grassland a coral reef a desert etc
Competition Interaction occurs within interspecific or intraspecific population for utilizing
common resources that are in short supply (exploitation) or if the resources are not in short
supply for their survival or reproduction are known as competition
Consumers Organisms that ingest organic food (usually particulate) or other organisms
Dynamics In population ecology the study of reasons for changes in population size contrast
with statics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms
(biotic community) and non-living substances (abiotic environment) interacting to produce an
exchange of materials between the living and non-living parts
Habitat The natural abode of an organism including its total environment
Mutualism A interspecific relationship between two or more species in which both or all
benefit from the association and cannot live separately
Niche The ecological role or profession of an organism in its ecosystem its activities and
relationships to its community and total environment
Population Groups of individuals of single species a group of interacting individuals in a
definable space
Symbiosis The living together of two or more species
Insect Ecology and Population Dynamics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms (biotic
community) and non-living substances (abiotic environment) interacting to produce an exchange
of materials between the living and non-living parts It may be as small as a puddle or as large as
the entire earth Further an ecosystem may be natural as a pond a lake a river an estuary an
ocean a forest etc or it may be man-made or artificial like an aquarium a dam a cropland a
garden an orchard a city and so on The term ecosystem was coined by a Ag Tansley (1935)-
its eco part means environment and the system part implies a complex of coordinated units
Structure of an ecosystem
From structural point of view all ecosystems consists of following four basic
components
1 Abiotic Substances
2 Biotic Substances factors
a Producers
b Consumers
c Reducers or Decomposers
Biotic Substances
These include basic inorganic and organic compounds of the environment or habitat of
the organism The inorganic compounds of an ecosystem are carbon dioxide water nitrogen
calcium phosphate all of which are involved in matter cycles The organic compounds of an
ecosystem are proteins carbohydrates lipids and amino acids all of which are synthesized by
the biota of an ecosystem and are reached to ecosystem as their wastes dead remains etc The
climate temperature light soil etc are other abiotic components of the ecosystem
Producers
Producers are autotrophic organisms like chemosynthetic and photosynthetic bacteria
blue green algae algae and all other green plants They are called ecosystem producers because
they capture energy from non-organic sources especially light and store some of the energy in
the form of chemical bonds for the later use
Insect Ecology and Population Dynamics
Consumers
They are heterotrophic organisms in the ecosystem which eat other living creatures
There are herbivorres which eat plants and carnivores which eat other animals They are also
called phagotrops or macroconsumers
Reducers or Decomposers
Reducers decomposers saprotrophs or microconsumers are heterotrophic organisms that
breakdown dead and waste matter Fungi and certain bacteria are the prime representatives of
this category
Examples of ecosystemA classic example of an ecosystem is a small lake or pond The abiotic or non-living parts
of a fresh water pond include the water dissolved oxygen carbon dioxide inorganic salts such
as phosphates nitrates and chlorides of sodium potassium and calcium and a multitude of
organic compounds such as amino acids humic acids etc The living part of the freshwater pond
can be subdivided according to the functions of the organisms ie what they contribute toward
keeping the ecosystem operating as a stable interacting whole In a freshwater pond there are
two types of producers the larger plants growing along the shore or floating in shallow water
and the microscopic floating plants most of which are algae that are distributed throughout the
water as deep as light will penetrate These tiny plants collectively referred to as phytoplankton
are usually not visible unless they are present in great abundance and give the water a greenish
tinge
The macroconsumers or phagotrophs of pond ecosystems include insects and insect
larvae Crustacea fish and perhaps some freshwater clams Primary consumers such as
zooplankton found near the surface of water and benthos are the plant eaters and secondary
consumers are the carnivores that eat the primary consumers
Types of ecosystemEllenberg (1973) has classified the world into a hierarchy of ecosystems Biosphere is
the largest and all-encompassing ecosystem Next lower level is mega-ecosystem such as
marine ecosystems (ie ecosystems of saline water of sea ocean and lake) limnic ecosystems
(ie ecosystems of fresh-water) semi-terrestrial ecosystems (ieecosystems of wet soil and
air) terrestrisl ecosystems (ieecosystems of aerated soil and air) and urban-industrial
ecosystems (man-made ecosystems like cropland city etc) The next-lower level is represented
Insect Ecology and Population Dynamics
by macro-ecosystems ( forests etc) within the mega ndashecosystem Meso-ecosystems (eg a
cold deciduous broad leaf foreat with its fauna) are considered as the basic units of thus scheme
Meso-ecosystems are sub divided into micro-ecosystems which depart with respect to a certain
component( a low land mountain or sub-alpine cold deciduous broad leaf forest with its fauna)
Nano-ecosystems are further small ecosystems which are spatially contained within larger
ecosystems and that show a certain individuality of their own
PopulationAll living organisms exist in groups of the same species or populations The word
population (L populus people) was originally referred to a group of people occupying a
particular space Thus a population can be defined as the tptal assemblage of individuals of the
same species occupying a particular space at a given time
Dispersion
Populations have a tendency to disperse or spread out in all directions until some barrier
is reached Accordingly population dispersion is the movement of individuals into or out of the
population area It takes three forms emigration-one way outward movement immigration-
one way inward movement and migration-periodic departure and return
Dispersion supplements natality and mortality in shaping population growth form and
density and also it plays a significant role in the distribution of plants and animals even to the
areas previously unoccupied by the members of the population Most types of population
dispersion occur due to a number of reasons such as for obtaining food avoiding predators
preventing overcrowding result of action of wind and water environmental factors as light and
temperature breeding behavior physiological reasons as secretion of some hormone or for
interchange of genetic material between populations
Emigration
Emigration under natural conditions occurs when there is overcrowding in the migratory
locust This is generally regarded as an adaptive behaviour that regulates the population on a
particular site and prevents overexploitation of the habitat Further it leads to occupation of new
areas elsewhere By dispersing into new localities there is opportunity gained for interbreeding
with other populations leading to more genetic geterozygosity and adaptability
Immigration
Insect Ecology and Population Dynamics
Immigration leads to a rise in population level causing an overpopulation which may
lead to an increase beyond the carrying capasity These immigrations result in increased
mortality among the immigrants or decreased reproductive capasity of the individuals Both
emigration and immigration are initiated by weather and other abiotic and biotic environmental
factors
Migration
Migration is a peculiar kind of population dispersion which involves the mass movement
of entire population This can occur only in mobile organism and best developed in insects like
the butterfly Dannaus plexippus and in the migratory dragonflies Libellula quadrimaculata and
Pantala flavescens
In most cases migration of population may occur for food shelter or reproduction
Types
There are two types of ecosystems that are of ecological interest-open and cybernetic
Open systems depends on an outside environment to provide inputs and accept outputs
The ecosystem is an open system for it receives energy from an outside source the sun fixes and
utilizes it and ultimately dissipates heat to space If the suns energy were to be cut off the
ecosystem would cease to function An open system can consist of a number of components or
parts called subsystem and each subsystem can consist of a number of elements
A cybernetic system which can also be an open system has some sort of feedback
system to make it self ndashregulating Most living systems possess cybernetic systems that can
function at various levels from the cell to the community but always functioning through
organisms-the difference being that in living systems the set point is not fixed
What is ecology
The scientific study of the interactions that determine the distribution and abundance of organisms
scientific study - process of observation and experimentation leading to the rejection of all but one hypothesis not the truth or fact but the best fitting explanation of all the observations
interactions - include both biotic and abiotic factors
distribution - where insects occur
Insect Ecology and Population Dynamics
abundance - a measurement of population size
from the point of view of agriculture studies of populations of insects and their interactions with the environment are often restricted to a unit we call an agroecosystem
- agroecosystems
may be extensive corn belt or wheat growing areas of the Great Plains of North America or
limited - isolated orchard consisting of a few acres plantedwith widely-spaced trees or a greenhouse
- agroecosystems regardless of size have some common characteristics including
(1) created and maintained by human effort
(2) agroecosystems often lack temporal continuity
(3) plant selection by humans
(4) in any particular system often reduced species diversity frequently a single species dominates
(5) uniform phenology
phenology defn the study of seasonal changes which give rise to the observed periodicity of biological phenomena
(6) addition of nutrients
(7) frequently occurring insect weed and disease outbreaks
Ecology (from the Greek oikos meaning house or dwelling and logos meaning discourse) is the study of the interactions of organisms with each other and their environment Always remember that Ecology is a SCIENCE not a sociopolitical movement (eg environmentalism) The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystemsThe ECOSYSTEM is all living communities (biotic) and their associated non-living (abiotic) environmental components in a defined area Examples in southern Florida Everglades - a shallow wetland or marsh Hammock - hardwood (ie flowering tree) forest on higher ground within the Everglades Pine rocklands ndash on higher ground maintained by fire which prevents hardwoodsfrom taking overCoral ReefEstuaryMangrove
Insect Ecology and Population Dynamics
Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
discovering new sources of food new unpolluting sources of energy and new methods of pest
control such as biological control which causes no environmental pollution
Some ecology related terminologyAbiotic factors Non-living ecological components of an ecosystem such water oxygen
sodium chloride nitrogen carbon dioxide etc and other physical and chemical influences such
as temperature light humidity pH etc
Biotic factors Living ecological components of an ecosystem such as producers
(chemosynthetic bacteria and photosynthetic green plants) consumers (heterotrophic animals
and decomposer organisms (bacteria fungi and other saprophytes)
Commensalism The living together of two species usually with benefit to one
Community A group of populations of plants and animals living together in a given place eg
the community of an oak forest a marsh a grassland a coral reef a desert etc
Competition Interaction occurs within interspecific or intraspecific population for utilizing
common resources that are in short supply (exploitation) or if the resources are not in short
supply for their survival or reproduction are known as competition
Consumers Organisms that ingest organic food (usually particulate) or other organisms
Dynamics In population ecology the study of reasons for changes in population size contrast
with statics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms
(biotic community) and non-living substances (abiotic environment) interacting to produce an
exchange of materials between the living and non-living parts
Habitat The natural abode of an organism including its total environment
Mutualism A interspecific relationship between two or more species in which both or all
benefit from the association and cannot live separately
Niche The ecological role or profession of an organism in its ecosystem its activities and
relationships to its community and total environment
Population Groups of individuals of single species a group of interacting individuals in a
definable space
Symbiosis The living together of two or more species
Insect Ecology and Population Dynamics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms (biotic
community) and non-living substances (abiotic environment) interacting to produce an exchange
of materials between the living and non-living parts It may be as small as a puddle or as large as
the entire earth Further an ecosystem may be natural as a pond a lake a river an estuary an
ocean a forest etc or it may be man-made or artificial like an aquarium a dam a cropland a
garden an orchard a city and so on The term ecosystem was coined by a Ag Tansley (1935)-
its eco part means environment and the system part implies a complex of coordinated units
Structure of an ecosystem
From structural point of view all ecosystems consists of following four basic
components
1 Abiotic Substances
2 Biotic Substances factors
a Producers
b Consumers
c Reducers or Decomposers
Biotic Substances
These include basic inorganic and organic compounds of the environment or habitat of
the organism The inorganic compounds of an ecosystem are carbon dioxide water nitrogen
calcium phosphate all of which are involved in matter cycles The organic compounds of an
ecosystem are proteins carbohydrates lipids and amino acids all of which are synthesized by
the biota of an ecosystem and are reached to ecosystem as their wastes dead remains etc The
climate temperature light soil etc are other abiotic components of the ecosystem
Producers
Producers are autotrophic organisms like chemosynthetic and photosynthetic bacteria
blue green algae algae and all other green plants They are called ecosystem producers because
they capture energy from non-organic sources especially light and store some of the energy in
the form of chemical bonds for the later use
Insect Ecology and Population Dynamics
Consumers
They are heterotrophic organisms in the ecosystem which eat other living creatures
There are herbivorres which eat plants and carnivores which eat other animals They are also
called phagotrops or macroconsumers
Reducers or Decomposers
Reducers decomposers saprotrophs or microconsumers are heterotrophic organisms that
breakdown dead and waste matter Fungi and certain bacteria are the prime representatives of
this category
Examples of ecosystemA classic example of an ecosystem is a small lake or pond The abiotic or non-living parts
of a fresh water pond include the water dissolved oxygen carbon dioxide inorganic salts such
as phosphates nitrates and chlorides of sodium potassium and calcium and a multitude of
organic compounds such as amino acids humic acids etc The living part of the freshwater pond
can be subdivided according to the functions of the organisms ie what they contribute toward
keeping the ecosystem operating as a stable interacting whole In a freshwater pond there are
two types of producers the larger plants growing along the shore or floating in shallow water
and the microscopic floating plants most of which are algae that are distributed throughout the
water as deep as light will penetrate These tiny plants collectively referred to as phytoplankton
are usually not visible unless they are present in great abundance and give the water a greenish
tinge
The macroconsumers or phagotrophs of pond ecosystems include insects and insect
larvae Crustacea fish and perhaps some freshwater clams Primary consumers such as
zooplankton found near the surface of water and benthos are the plant eaters and secondary
consumers are the carnivores that eat the primary consumers
Types of ecosystemEllenberg (1973) has classified the world into a hierarchy of ecosystems Biosphere is
the largest and all-encompassing ecosystem Next lower level is mega-ecosystem such as
marine ecosystems (ie ecosystems of saline water of sea ocean and lake) limnic ecosystems
(ie ecosystems of fresh-water) semi-terrestrial ecosystems (ieecosystems of wet soil and
air) terrestrisl ecosystems (ieecosystems of aerated soil and air) and urban-industrial
ecosystems (man-made ecosystems like cropland city etc) The next-lower level is represented
Insect Ecology and Population Dynamics
by macro-ecosystems ( forests etc) within the mega ndashecosystem Meso-ecosystems (eg a
cold deciduous broad leaf foreat with its fauna) are considered as the basic units of thus scheme
Meso-ecosystems are sub divided into micro-ecosystems which depart with respect to a certain
component( a low land mountain or sub-alpine cold deciduous broad leaf forest with its fauna)
Nano-ecosystems are further small ecosystems which are spatially contained within larger
ecosystems and that show a certain individuality of their own
PopulationAll living organisms exist in groups of the same species or populations The word
population (L populus people) was originally referred to a group of people occupying a
particular space Thus a population can be defined as the tptal assemblage of individuals of the
same species occupying a particular space at a given time
Dispersion
Populations have a tendency to disperse or spread out in all directions until some barrier
is reached Accordingly population dispersion is the movement of individuals into or out of the
population area It takes three forms emigration-one way outward movement immigration-
one way inward movement and migration-periodic departure and return
Dispersion supplements natality and mortality in shaping population growth form and
density and also it plays a significant role in the distribution of plants and animals even to the
areas previously unoccupied by the members of the population Most types of population
dispersion occur due to a number of reasons such as for obtaining food avoiding predators
preventing overcrowding result of action of wind and water environmental factors as light and
temperature breeding behavior physiological reasons as secretion of some hormone or for
interchange of genetic material between populations
Emigration
Emigration under natural conditions occurs when there is overcrowding in the migratory
locust This is generally regarded as an adaptive behaviour that regulates the population on a
particular site and prevents overexploitation of the habitat Further it leads to occupation of new
areas elsewhere By dispersing into new localities there is opportunity gained for interbreeding
with other populations leading to more genetic geterozygosity and adaptability
Immigration
Insect Ecology and Population Dynamics
Immigration leads to a rise in population level causing an overpopulation which may
lead to an increase beyond the carrying capasity These immigrations result in increased
mortality among the immigrants or decreased reproductive capasity of the individuals Both
emigration and immigration are initiated by weather and other abiotic and biotic environmental
factors
Migration
Migration is a peculiar kind of population dispersion which involves the mass movement
of entire population This can occur only in mobile organism and best developed in insects like
the butterfly Dannaus plexippus and in the migratory dragonflies Libellula quadrimaculata and
Pantala flavescens
In most cases migration of population may occur for food shelter or reproduction
Types
There are two types of ecosystems that are of ecological interest-open and cybernetic
Open systems depends on an outside environment to provide inputs and accept outputs
The ecosystem is an open system for it receives energy from an outside source the sun fixes and
utilizes it and ultimately dissipates heat to space If the suns energy were to be cut off the
ecosystem would cease to function An open system can consist of a number of components or
parts called subsystem and each subsystem can consist of a number of elements
A cybernetic system which can also be an open system has some sort of feedback
system to make it self ndashregulating Most living systems possess cybernetic systems that can
function at various levels from the cell to the community but always functioning through
organisms-the difference being that in living systems the set point is not fixed
What is ecology
The scientific study of the interactions that determine the distribution and abundance of organisms
scientific study - process of observation and experimentation leading to the rejection of all but one hypothesis not the truth or fact but the best fitting explanation of all the observations
interactions - include both biotic and abiotic factors
distribution - where insects occur
Insect Ecology and Population Dynamics
abundance - a measurement of population size
from the point of view of agriculture studies of populations of insects and their interactions with the environment are often restricted to a unit we call an agroecosystem
- agroecosystems
may be extensive corn belt or wheat growing areas of the Great Plains of North America or
limited - isolated orchard consisting of a few acres plantedwith widely-spaced trees or a greenhouse
- agroecosystems regardless of size have some common characteristics including
(1) created and maintained by human effort
(2) agroecosystems often lack temporal continuity
(3) plant selection by humans
(4) in any particular system often reduced species diversity frequently a single species dominates
(5) uniform phenology
phenology defn the study of seasonal changes which give rise to the observed periodicity of biological phenomena
(6) addition of nutrients
(7) frequently occurring insect weed and disease outbreaks
Ecology (from the Greek oikos meaning house or dwelling and logos meaning discourse) is the study of the interactions of organisms with each other and their environment Always remember that Ecology is a SCIENCE not a sociopolitical movement (eg environmentalism) The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystemsThe ECOSYSTEM is all living communities (biotic) and their associated non-living (abiotic) environmental components in a defined area Examples in southern Florida Everglades - a shallow wetland or marsh Hammock - hardwood (ie flowering tree) forest on higher ground within the Everglades Pine rocklands ndash on higher ground maintained by fire which prevents hardwoodsfrom taking overCoral ReefEstuaryMangrove
Insect Ecology and Population Dynamics
Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms (biotic
community) and non-living substances (abiotic environment) interacting to produce an exchange
of materials between the living and non-living parts It may be as small as a puddle or as large as
the entire earth Further an ecosystem may be natural as a pond a lake a river an estuary an
ocean a forest etc or it may be man-made or artificial like an aquarium a dam a cropland a
garden an orchard a city and so on The term ecosystem was coined by a Ag Tansley (1935)-
its eco part means environment and the system part implies a complex of coordinated units
Structure of an ecosystem
From structural point of view all ecosystems consists of following four basic
components
1 Abiotic Substances
2 Biotic Substances factors
a Producers
b Consumers
c Reducers or Decomposers
Biotic Substances
These include basic inorganic and organic compounds of the environment or habitat of
the organism The inorganic compounds of an ecosystem are carbon dioxide water nitrogen
calcium phosphate all of which are involved in matter cycles The organic compounds of an
ecosystem are proteins carbohydrates lipids and amino acids all of which are synthesized by
the biota of an ecosystem and are reached to ecosystem as their wastes dead remains etc The
climate temperature light soil etc are other abiotic components of the ecosystem
Producers
Producers are autotrophic organisms like chemosynthetic and photosynthetic bacteria
blue green algae algae and all other green plants They are called ecosystem producers because
they capture energy from non-organic sources especially light and store some of the energy in
the form of chemical bonds for the later use
Insect Ecology and Population Dynamics
Consumers
They are heterotrophic organisms in the ecosystem which eat other living creatures
There are herbivorres which eat plants and carnivores which eat other animals They are also
called phagotrops or macroconsumers
Reducers or Decomposers
Reducers decomposers saprotrophs or microconsumers are heterotrophic organisms that
breakdown dead and waste matter Fungi and certain bacteria are the prime representatives of
this category
Examples of ecosystemA classic example of an ecosystem is a small lake or pond The abiotic or non-living parts
of a fresh water pond include the water dissolved oxygen carbon dioxide inorganic salts such
as phosphates nitrates and chlorides of sodium potassium and calcium and a multitude of
organic compounds such as amino acids humic acids etc The living part of the freshwater pond
can be subdivided according to the functions of the organisms ie what they contribute toward
keeping the ecosystem operating as a stable interacting whole In a freshwater pond there are
two types of producers the larger plants growing along the shore or floating in shallow water
and the microscopic floating plants most of which are algae that are distributed throughout the
water as deep as light will penetrate These tiny plants collectively referred to as phytoplankton
are usually not visible unless they are present in great abundance and give the water a greenish
tinge
The macroconsumers or phagotrophs of pond ecosystems include insects and insect
larvae Crustacea fish and perhaps some freshwater clams Primary consumers such as
zooplankton found near the surface of water and benthos are the plant eaters and secondary
consumers are the carnivores that eat the primary consumers
Types of ecosystemEllenberg (1973) has classified the world into a hierarchy of ecosystems Biosphere is
the largest and all-encompassing ecosystem Next lower level is mega-ecosystem such as
marine ecosystems (ie ecosystems of saline water of sea ocean and lake) limnic ecosystems
(ie ecosystems of fresh-water) semi-terrestrial ecosystems (ieecosystems of wet soil and
air) terrestrisl ecosystems (ieecosystems of aerated soil and air) and urban-industrial
ecosystems (man-made ecosystems like cropland city etc) The next-lower level is represented
Insect Ecology and Population Dynamics
by macro-ecosystems ( forests etc) within the mega ndashecosystem Meso-ecosystems (eg a
cold deciduous broad leaf foreat with its fauna) are considered as the basic units of thus scheme
Meso-ecosystems are sub divided into micro-ecosystems which depart with respect to a certain
component( a low land mountain or sub-alpine cold deciduous broad leaf forest with its fauna)
Nano-ecosystems are further small ecosystems which are spatially contained within larger
ecosystems and that show a certain individuality of their own
PopulationAll living organisms exist in groups of the same species or populations The word
population (L populus people) was originally referred to a group of people occupying a
particular space Thus a population can be defined as the tptal assemblage of individuals of the
same species occupying a particular space at a given time
Dispersion
Populations have a tendency to disperse or spread out in all directions until some barrier
is reached Accordingly population dispersion is the movement of individuals into or out of the
population area It takes three forms emigration-one way outward movement immigration-
one way inward movement and migration-periodic departure and return
Dispersion supplements natality and mortality in shaping population growth form and
density and also it plays a significant role in the distribution of plants and animals even to the
areas previously unoccupied by the members of the population Most types of population
dispersion occur due to a number of reasons such as for obtaining food avoiding predators
preventing overcrowding result of action of wind and water environmental factors as light and
temperature breeding behavior physiological reasons as secretion of some hormone or for
interchange of genetic material between populations
Emigration
Emigration under natural conditions occurs when there is overcrowding in the migratory
locust This is generally regarded as an adaptive behaviour that regulates the population on a
particular site and prevents overexploitation of the habitat Further it leads to occupation of new
areas elsewhere By dispersing into new localities there is opportunity gained for interbreeding
with other populations leading to more genetic geterozygosity and adaptability
Immigration
Insect Ecology and Population Dynamics
Immigration leads to a rise in population level causing an overpopulation which may
lead to an increase beyond the carrying capasity These immigrations result in increased
mortality among the immigrants or decreased reproductive capasity of the individuals Both
emigration and immigration are initiated by weather and other abiotic and biotic environmental
factors
Migration
Migration is a peculiar kind of population dispersion which involves the mass movement
of entire population This can occur only in mobile organism and best developed in insects like
the butterfly Dannaus plexippus and in the migratory dragonflies Libellula quadrimaculata and
Pantala flavescens
In most cases migration of population may occur for food shelter or reproduction
Types
There are two types of ecosystems that are of ecological interest-open and cybernetic
Open systems depends on an outside environment to provide inputs and accept outputs
The ecosystem is an open system for it receives energy from an outside source the sun fixes and
utilizes it and ultimately dissipates heat to space If the suns energy were to be cut off the
ecosystem would cease to function An open system can consist of a number of components or
parts called subsystem and each subsystem can consist of a number of elements
A cybernetic system which can also be an open system has some sort of feedback
system to make it self ndashregulating Most living systems possess cybernetic systems that can
function at various levels from the cell to the community but always functioning through
organisms-the difference being that in living systems the set point is not fixed
What is ecology
The scientific study of the interactions that determine the distribution and abundance of organisms
scientific study - process of observation and experimentation leading to the rejection of all but one hypothesis not the truth or fact but the best fitting explanation of all the observations
interactions - include both biotic and abiotic factors
distribution - where insects occur
Insect Ecology and Population Dynamics
abundance - a measurement of population size
from the point of view of agriculture studies of populations of insects and their interactions with the environment are often restricted to a unit we call an agroecosystem
- agroecosystems
may be extensive corn belt or wheat growing areas of the Great Plains of North America or
limited - isolated orchard consisting of a few acres plantedwith widely-spaced trees or a greenhouse
- agroecosystems regardless of size have some common characteristics including
(1) created and maintained by human effort
(2) agroecosystems often lack temporal continuity
(3) plant selection by humans
(4) in any particular system often reduced species diversity frequently a single species dominates
(5) uniform phenology
phenology defn the study of seasonal changes which give rise to the observed periodicity of biological phenomena
(6) addition of nutrients
(7) frequently occurring insect weed and disease outbreaks
Ecology (from the Greek oikos meaning house or dwelling and logos meaning discourse) is the study of the interactions of organisms with each other and their environment Always remember that Ecology is a SCIENCE not a sociopolitical movement (eg environmentalism) The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystemsThe ECOSYSTEM is all living communities (biotic) and their associated non-living (abiotic) environmental components in a defined area Examples in southern Florida Everglades - a shallow wetland or marsh Hammock - hardwood (ie flowering tree) forest on higher ground within the Everglades Pine rocklands ndash on higher ground maintained by fire which prevents hardwoodsfrom taking overCoral ReefEstuaryMangrove
Insect Ecology and Population Dynamics
Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Consumers
They are heterotrophic organisms in the ecosystem which eat other living creatures
There are herbivorres which eat plants and carnivores which eat other animals They are also
called phagotrops or macroconsumers
Reducers or Decomposers
Reducers decomposers saprotrophs or microconsumers are heterotrophic organisms that
breakdown dead and waste matter Fungi and certain bacteria are the prime representatives of
this category
Examples of ecosystemA classic example of an ecosystem is a small lake or pond The abiotic or non-living parts
of a fresh water pond include the water dissolved oxygen carbon dioxide inorganic salts such
as phosphates nitrates and chlorides of sodium potassium and calcium and a multitude of
organic compounds such as amino acids humic acids etc The living part of the freshwater pond
can be subdivided according to the functions of the organisms ie what they contribute toward
keeping the ecosystem operating as a stable interacting whole In a freshwater pond there are
two types of producers the larger plants growing along the shore or floating in shallow water
and the microscopic floating plants most of which are algae that are distributed throughout the
water as deep as light will penetrate These tiny plants collectively referred to as phytoplankton
are usually not visible unless they are present in great abundance and give the water a greenish
tinge
The macroconsumers or phagotrophs of pond ecosystems include insects and insect
larvae Crustacea fish and perhaps some freshwater clams Primary consumers such as
zooplankton found near the surface of water and benthos are the plant eaters and secondary
consumers are the carnivores that eat the primary consumers
Types of ecosystemEllenberg (1973) has classified the world into a hierarchy of ecosystems Biosphere is
the largest and all-encompassing ecosystem Next lower level is mega-ecosystem such as
marine ecosystems (ie ecosystems of saline water of sea ocean and lake) limnic ecosystems
(ie ecosystems of fresh-water) semi-terrestrial ecosystems (ieecosystems of wet soil and
air) terrestrisl ecosystems (ieecosystems of aerated soil and air) and urban-industrial
ecosystems (man-made ecosystems like cropland city etc) The next-lower level is represented
Insect Ecology and Population Dynamics
by macro-ecosystems ( forests etc) within the mega ndashecosystem Meso-ecosystems (eg a
cold deciduous broad leaf foreat with its fauna) are considered as the basic units of thus scheme
Meso-ecosystems are sub divided into micro-ecosystems which depart with respect to a certain
component( a low land mountain or sub-alpine cold deciduous broad leaf forest with its fauna)
Nano-ecosystems are further small ecosystems which are spatially contained within larger
ecosystems and that show a certain individuality of their own
PopulationAll living organisms exist in groups of the same species or populations The word
population (L populus people) was originally referred to a group of people occupying a
particular space Thus a population can be defined as the tptal assemblage of individuals of the
same species occupying a particular space at a given time
Dispersion
Populations have a tendency to disperse or spread out in all directions until some barrier
is reached Accordingly population dispersion is the movement of individuals into or out of the
population area It takes three forms emigration-one way outward movement immigration-
one way inward movement and migration-periodic departure and return
Dispersion supplements natality and mortality in shaping population growth form and
density and also it plays a significant role in the distribution of plants and animals even to the
areas previously unoccupied by the members of the population Most types of population
dispersion occur due to a number of reasons such as for obtaining food avoiding predators
preventing overcrowding result of action of wind and water environmental factors as light and
temperature breeding behavior physiological reasons as secretion of some hormone or for
interchange of genetic material between populations
Emigration
Emigration under natural conditions occurs when there is overcrowding in the migratory
locust This is generally regarded as an adaptive behaviour that regulates the population on a
particular site and prevents overexploitation of the habitat Further it leads to occupation of new
areas elsewhere By dispersing into new localities there is opportunity gained for interbreeding
with other populations leading to more genetic geterozygosity and adaptability
Immigration
Insect Ecology and Population Dynamics
Immigration leads to a rise in population level causing an overpopulation which may
lead to an increase beyond the carrying capasity These immigrations result in increased
mortality among the immigrants or decreased reproductive capasity of the individuals Both
emigration and immigration are initiated by weather and other abiotic and biotic environmental
factors
Migration
Migration is a peculiar kind of population dispersion which involves the mass movement
of entire population This can occur only in mobile organism and best developed in insects like
the butterfly Dannaus plexippus and in the migratory dragonflies Libellula quadrimaculata and
Pantala flavescens
In most cases migration of population may occur for food shelter or reproduction
Types
There are two types of ecosystems that are of ecological interest-open and cybernetic
Open systems depends on an outside environment to provide inputs and accept outputs
The ecosystem is an open system for it receives energy from an outside source the sun fixes and
utilizes it and ultimately dissipates heat to space If the suns energy were to be cut off the
ecosystem would cease to function An open system can consist of a number of components or
parts called subsystem and each subsystem can consist of a number of elements
A cybernetic system which can also be an open system has some sort of feedback
system to make it self ndashregulating Most living systems possess cybernetic systems that can
function at various levels from the cell to the community but always functioning through
organisms-the difference being that in living systems the set point is not fixed
What is ecology
The scientific study of the interactions that determine the distribution and abundance of organisms
scientific study - process of observation and experimentation leading to the rejection of all but one hypothesis not the truth or fact but the best fitting explanation of all the observations
interactions - include both biotic and abiotic factors
distribution - where insects occur
Insect Ecology and Population Dynamics
abundance - a measurement of population size
from the point of view of agriculture studies of populations of insects and their interactions with the environment are often restricted to a unit we call an agroecosystem
- agroecosystems
may be extensive corn belt or wheat growing areas of the Great Plains of North America or
limited - isolated orchard consisting of a few acres plantedwith widely-spaced trees or a greenhouse
- agroecosystems regardless of size have some common characteristics including
(1) created and maintained by human effort
(2) agroecosystems often lack temporal continuity
(3) plant selection by humans
(4) in any particular system often reduced species diversity frequently a single species dominates
(5) uniform phenology
phenology defn the study of seasonal changes which give rise to the observed periodicity of biological phenomena
(6) addition of nutrients
(7) frequently occurring insect weed and disease outbreaks
Ecology (from the Greek oikos meaning house or dwelling and logos meaning discourse) is the study of the interactions of organisms with each other and their environment Always remember that Ecology is a SCIENCE not a sociopolitical movement (eg environmentalism) The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystemsThe ECOSYSTEM is all living communities (biotic) and their associated non-living (abiotic) environmental components in a defined area Examples in southern Florida Everglades - a shallow wetland or marsh Hammock - hardwood (ie flowering tree) forest on higher ground within the Everglades Pine rocklands ndash on higher ground maintained by fire which prevents hardwoodsfrom taking overCoral ReefEstuaryMangrove
Insect Ecology and Population Dynamics
Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
by macro-ecosystems ( forests etc) within the mega ndashecosystem Meso-ecosystems (eg a
cold deciduous broad leaf foreat with its fauna) are considered as the basic units of thus scheme
Meso-ecosystems are sub divided into micro-ecosystems which depart with respect to a certain
component( a low land mountain or sub-alpine cold deciduous broad leaf forest with its fauna)
Nano-ecosystems are further small ecosystems which are spatially contained within larger
ecosystems and that show a certain individuality of their own
PopulationAll living organisms exist in groups of the same species or populations The word
population (L populus people) was originally referred to a group of people occupying a
particular space Thus a population can be defined as the tptal assemblage of individuals of the
same species occupying a particular space at a given time
Dispersion
Populations have a tendency to disperse or spread out in all directions until some barrier
is reached Accordingly population dispersion is the movement of individuals into or out of the
population area It takes three forms emigration-one way outward movement immigration-
one way inward movement and migration-periodic departure and return
Dispersion supplements natality and mortality in shaping population growth form and
density and also it plays a significant role in the distribution of plants and animals even to the
areas previously unoccupied by the members of the population Most types of population
dispersion occur due to a number of reasons such as for obtaining food avoiding predators
preventing overcrowding result of action of wind and water environmental factors as light and
temperature breeding behavior physiological reasons as secretion of some hormone or for
interchange of genetic material between populations
Emigration
Emigration under natural conditions occurs when there is overcrowding in the migratory
locust This is generally regarded as an adaptive behaviour that regulates the population on a
particular site and prevents overexploitation of the habitat Further it leads to occupation of new
areas elsewhere By dispersing into new localities there is opportunity gained for interbreeding
with other populations leading to more genetic geterozygosity and adaptability
Immigration
Insect Ecology and Population Dynamics
Immigration leads to a rise in population level causing an overpopulation which may
lead to an increase beyond the carrying capasity These immigrations result in increased
mortality among the immigrants or decreased reproductive capasity of the individuals Both
emigration and immigration are initiated by weather and other abiotic and biotic environmental
factors
Migration
Migration is a peculiar kind of population dispersion which involves the mass movement
of entire population This can occur only in mobile organism and best developed in insects like
the butterfly Dannaus plexippus and in the migratory dragonflies Libellula quadrimaculata and
Pantala flavescens
In most cases migration of population may occur for food shelter or reproduction
Types
There are two types of ecosystems that are of ecological interest-open and cybernetic
Open systems depends on an outside environment to provide inputs and accept outputs
The ecosystem is an open system for it receives energy from an outside source the sun fixes and
utilizes it and ultimately dissipates heat to space If the suns energy were to be cut off the
ecosystem would cease to function An open system can consist of a number of components or
parts called subsystem and each subsystem can consist of a number of elements
A cybernetic system which can also be an open system has some sort of feedback
system to make it self ndashregulating Most living systems possess cybernetic systems that can
function at various levels from the cell to the community but always functioning through
organisms-the difference being that in living systems the set point is not fixed
What is ecology
The scientific study of the interactions that determine the distribution and abundance of organisms
scientific study - process of observation and experimentation leading to the rejection of all but one hypothesis not the truth or fact but the best fitting explanation of all the observations
interactions - include both biotic and abiotic factors
distribution - where insects occur
Insect Ecology and Population Dynamics
abundance - a measurement of population size
from the point of view of agriculture studies of populations of insects and their interactions with the environment are often restricted to a unit we call an agroecosystem
- agroecosystems
may be extensive corn belt or wheat growing areas of the Great Plains of North America or
limited - isolated orchard consisting of a few acres plantedwith widely-spaced trees or a greenhouse
- agroecosystems regardless of size have some common characteristics including
(1) created and maintained by human effort
(2) agroecosystems often lack temporal continuity
(3) plant selection by humans
(4) in any particular system often reduced species diversity frequently a single species dominates
(5) uniform phenology
phenology defn the study of seasonal changes which give rise to the observed periodicity of biological phenomena
(6) addition of nutrients
(7) frequently occurring insect weed and disease outbreaks
Ecology (from the Greek oikos meaning house or dwelling and logos meaning discourse) is the study of the interactions of organisms with each other and their environment Always remember that Ecology is a SCIENCE not a sociopolitical movement (eg environmentalism) The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystemsThe ECOSYSTEM is all living communities (biotic) and their associated non-living (abiotic) environmental components in a defined area Examples in southern Florida Everglades - a shallow wetland or marsh Hammock - hardwood (ie flowering tree) forest on higher ground within the Everglades Pine rocklands ndash on higher ground maintained by fire which prevents hardwoodsfrom taking overCoral ReefEstuaryMangrove
Insect Ecology and Population Dynamics
Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Immigration leads to a rise in population level causing an overpopulation which may
lead to an increase beyond the carrying capasity These immigrations result in increased
mortality among the immigrants or decreased reproductive capasity of the individuals Both
emigration and immigration are initiated by weather and other abiotic and biotic environmental
factors
Migration
Migration is a peculiar kind of population dispersion which involves the mass movement
of entire population This can occur only in mobile organism and best developed in insects like
the butterfly Dannaus plexippus and in the migratory dragonflies Libellula quadrimaculata and
Pantala flavescens
In most cases migration of population may occur for food shelter or reproduction
Types
There are two types of ecosystems that are of ecological interest-open and cybernetic
Open systems depends on an outside environment to provide inputs and accept outputs
The ecosystem is an open system for it receives energy from an outside source the sun fixes and
utilizes it and ultimately dissipates heat to space If the suns energy were to be cut off the
ecosystem would cease to function An open system can consist of a number of components or
parts called subsystem and each subsystem can consist of a number of elements
A cybernetic system which can also be an open system has some sort of feedback
system to make it self ndashregulating Most living systems possess cybernetic systems that can
function at various levels from the cell to the community but always functioning through
organisms-the difference being that in living systems the set point is not fixed
What is ecology
The scientific study of the interactions that determine the distribution and abundance of organisms
scientific study - process of observation and experimentation leading to the rejection of all but one hypothesis not the truth or fact but the best fitting explanation of all the observations
interactions - include both biotic and abiotic factors
distribution - where insects occur
Insect Ecology and Population Dynamics
abundance - a measurement of population size
from the point of view of agriculture studies of populations of insects and their interactions with the environment are often restricted to a unit we call an agroecosystem
- agroecosystems
may be extensive corn belt or wheat growing areas of the Great Plains of North America or
limited - isolated orchard consisting of a few acres plantedwith widely-spaced trees or a greenhouse
- agroecosystems regardless of size have some common characteristics including
(1) created and maintained by human effort
(2) agroecosystems often lack temporal continuity
(3) plant selection by humans
(4) in any particular system often reduced species diversity frequently a single species dominates
(5) uniform phenology
phenology defn the study of seasonal changes which give rise to the observed periodicity of biological phenomena
(6) addition of nutrients
(7) frequently occurring insect weed and disease outbreaks
Ecology (from the Greek oikos meaning house or dwelling and logos meaning discourse) is the study of the interactions of organisms with each other and their environment Always remember that Ecology is a SCIENCE not a sociopolitical movement (eg environmentalism) The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystemsThe ECOSYSTEM is all living communities (biotic) and their associated non-living (abiotic) environmental components in a defined area Examples in southern Florida Everglades - a shallow wetland or marsh Hammock - hardwood (ie flowering tree) forest on higher ground within the Everglades Pine rocklands ndash on higher ground maintained by fire which prevents hardwoodsfrom taking overCoral ReefEstuaryMangrove
Insect Ecology and Population Dynamics
Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
abundance - a measurement of population size
from the point of view of agriculture studies of populations of insects and their interactions with the environment are often restricted to a unit we call an agroecosystem
- agroecosystems
may be extensive corn belt or wheat growing areas of the Great Plains of North America or
limited - isolated orchard consisting of a few acres plantedwith widely-spaced trees or a greenhouse
- agroecosystems regardless of size have some common characteristics including
(1) created and maintained by human effort
(2) agroecosystems often lack temporal continuity
(3) plant selection by humans
(4) in any particular system often reduced species diversity frequently a single species dominates
(5) uniform phenology
phenology defn the study of seasonal changes which give rise to the observed periodicity of biological phenomena
(6) addition of nutrients
(7) frequently occurring insect weed and disease outbreaks
Ecology (from the Greek oikos meaning house or dwelling and logos meaning discourse) is the study of the interactions of organisms with each other and their environment Always remember that Ecology is a SCIENCE not a sociopolitical movement (eg environmentalism) The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystemsThe ECOSYSTEM is all living communities (biotic) and their associated non-living (abiotic) environmental components in a defined area Examples in southern Florida Everglades - a shallow wetland or marsh Hammock - hardwood (ie flowering tree) forest on higher ground within the Everglades Pine rocklands ndash on higher ground maintained by fire which prevents hardwoodsfrom taking overCoral ReefEstuaryMangrove
Insect Ecology and Population Dynamics
Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and
Predators) are more
Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination
of hosts But the predator never eliminates the prey completely
1) density - insects per unit area
2) dispersion - spatial arrangement of the insects in the landscape
a regularuniform b random c clumpedaggregated
3) dispersal - not trivial movements but immigration into an area or emigration from an area
long distance
eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here
short distance (on a more local level)
(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant
4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight
univoltine - single generation in a year (many pest insect species especially in cooler regions)
multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat
- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC
- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
5) natality - birth rates
6) mortality - death rates - mortality is caused by numerous factors
ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition
ABIOTIC
- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important
- insects are found at the limits of their range perspective of abiotic factors
- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect
e g turn over the soil for insects which overwinter as pupae in the soil
1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects
2) moisture - moisture conditions may significantly infuence insect survival
- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well
3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive
- heavy rains can dislodge young insects from foliage and these are subsequently destroyed
4) climate - interaction of the previous factors and others
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects
e g difficult to establish
a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active
BIOTIC
1) predators 2) parasites and 3) disease (natural enemies)
- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities
- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low
- under natural conditions increases in population densities of natural enemies lag behind that of their hosts
4) competition
i interspecific -different species competing for the same resources
eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture
ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites
eg Pupation sites for overwintering codling moth
clean up debris prepare trap sites - banding trees with cloth
-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis
-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment
(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited
Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Resources can include food water light oxygen mates shelter breeding sites nesting space and so on
Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent
(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip
EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors
Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others
Major Areas of Ecology
Population Ecology Study of population growth and factors that affect growth
Community Ecology Study of interactions among species ecological succession
Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems
Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth
Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time
Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion
Density and numbers
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size
Insect Ecology and Population Dynamics
Counting individuals to determine density and population size