1 Populations, Communities, and Species Interaction Chapter 3
Slide 2 2 Outline: Critical Factors and Tolerance Limits Adaptation
and Natural Selection Speciation Taxonomy Ecological Niche Species
Interaction Population Growth Community Properties and Structure
Succession Slide 3 3 Population,Communities & Species
Interaction Why, where and How? Why a particular organism lives in
a particular area? Where he lives and how it interacts with its
environment? How he deals with environmental stresses? Why one
species is dominant over the other? How species interact with each
other in a community to survive? Slide 4 4 Critical Factors and
Tolerance Limits Environmental factors should be within tolerable
limit for organims to survive Critical Factor - Single factor in
shortest supply relative to demand is a critical determinant in
species distribution. Tolerance Limits refer to minimum and maximum
levels beyond which a particular species cannot survive or
reproduce. - Many species exhibit tolerance limits that are more
critical for young than adults. Slide 5 5 Tolerance Limits Slide 6
6 Adaptation Adaptation - Process where species acquire traits that
allow them to survive in their environments. Limited range of
physiological modifications. E.g transferring an indoor winter
plant outside to outside during spring. Inheritance of specific
genetic traits allowing a species to live in a particular
environment. Is explained by the theory of Evolution (Charles
Darwin). Slide 7 7 Natural Selection Natural Selection - Describes
process where better competitors survive and reproduce more
successfully. Small, spontaneous, random mutations occur in every
population creating genetic diversity& one trait could be
better than other, means of survival. Limited resources or
environmental conditions may exert selective pressure on a
population (influence fertility or survivorship in nature). Slide 8
8 Factors Exerting Selective Pressure Physiological stress due to
in appropriate levels of a critical environmental factor. Moisture,
Light, pH, temperature Predation includes Parasitism, Disease
Competition: Some organisms when they move to new habitat, may be
just lucky to survive than better suited. Slide 9 9 Speciation
Given enough time, mutations may collectively allow a species to
become better suited to new environmental conditions. Evolution
sometimes creates entirely new species, physically distinct from
their ancestors. Divergent Evolution- Separation of one species
into new species even though they occupy the same territory.
Compare the Cheetahs with House cat. Convergent Evolution-
Unrelated organisms evolve to look and act alike. E.g Fruit eating
Galapagos finch looks and behave like the parrots but they are
genetically different. Slide 10 10 Taxonomic Naming System Binomial
- based on Latin. Taxonomic classification of Corn: Kingdom -
Plantae Phylum-Anthophyta Class-Monocotyledons Order-Commenales
Family-Poaceae Genus -Zea Species-Zea Mays Refer pg 54 Table 3.1
for Humans. Slide 11 11 Ecological Niche Habitat - Set of
environmental conditions in which a particular organism lives.
Ecological Niche is described as either A description of role
played by a species in a biological community or A total set of
environmental factors that determines species distribution.
Generalists A broad niche eg Racoons have a wide range of habitat.
Specialists A narrow niche e.g Panda occupy a specific habitat.
Slide 12 12 Resource Partitioning Slide 13 13 Ecological Niche
Resource Partitioning - Alter behavior or physiology to minimize
competition ( Move to other areas, or become extinct). Partition
then allows several species to utilize different parts of the same
resource and co exists within a single habitat). Slide 14 14
Ecological Niche of Wood Warblers Slide 15 15 Weedy Species
Opportunistic Species - Quickly appear when opportunities arise.
Many weeds e.g the Dandelions Pioneer Species The opportunistics
can quickly colonize open, disturbed, or bare ground.They can be
useful in minimising soil erosion or a nuisnance. Slide 16 16
SPECIES INTERACTION Predation Any organism that feeds directly on
another living organism is termed a predator. Predation influences
population balance of communities involving: - All stages of life
cycles of predator and prey. - Specialized food-obtaining
mechanisms. - Specific predator-prey adaptations. Predation can
exert selective pressures which is called co-evolution (both
predator and prey adapt to suit the situation, both adapt to new
situation and allow the sps to survive and evolve. Slide 17 17
Competition Intraspecific - Competition among members of the same
species e.g Within a patch of grass,,some are tall, some
dwarf,some, sickly looking.all plants of the same sps absorb the
same nutrients for growth. To survive they are aided by: Dispersal
( e.g seed dispersal by wind, air, Rain Territoriality : Defending
resource-rich area, primarily against members of own species
Resource Partitioning (to reduce intraspecies competition, sps move
away from area) Interspecific - Competition between members of
different species for the same nutrients. E.g Different sps of
birds feeding for the same plot of corn. Slide 18 18 Symbiosis
Symbiosis - Intimate living together of members of two or more
species for mutual benefits. Types: Commensalism - One member
benefits while other is neither benefited nor harmed. - Cattle and
Cattle Egrets Mutualism - Both members benefit. - Lichens (Fungus
and cyanobacterium) Parasitism - One member benefits at the expense
of other. Humans and Tapeworms Slide 19 19 Defensive Mechanisms
Batesian Mimicry (H.W Bates,1857)- Harmless species evolve
characteristics that mimic unpalatable or poisonous species.E.g the
Wasp & the longhorn beetle (Pg 60) Mullerian Mimicry (F.
Miller,1878) - Two unpalatable or dangerous species evolve to look
alike.E.g several species of mushrooms looks alike and produce
fungal toxin which may be deadly. Slide 20 20 POPULATION DYNAMICS
Population Growth Exponential Growth - Growth as a percentage of
the whole :dN/dt=rN dN= change in numbers of individual Dt= change
in time R= rate of growth N= no. of individuals in a population
Biotic Potential - Potential of a population to grow in the absence
of expansion limitations (if nothing was limiting its expansion).
Slide 21 21 Limiting Factors Population growth is regulated by
internal ( Maturity, body size, hormones) & external factors
(Food, habitat, interaction). Environmental Resistance (factors
which reduce pop growth rates) Density-Dependent Factors -
Mortality rates increase as the density of the population
increases. Pop density is dependent on: E.g: Disease, Stress,
Predation Density-Independent Factors - Effect on mortality rate is
independent of population density. - Abiotic conditions eg drought,
frost may kill mosquito pop.immaterials of the number with which
they started the pop. Slide 22 22 Abundance -Total number of
organisms in a community. Diversity - Number of different species,
ecological niches, or genetic variation Complexity - Number of
species at each trophic level, and the number of trophic levels, in
a community. Slide 23 23 Slide 24 24 Resilience and Stability
Constancy (Lack of fluctuation) Inertia (Resistance to pertubation)
Renewal (Ability to repair damage) Slide 25 25 Community Structure
Randomly Arranged Individuals live wherever resources are
available. Clumped Individuals cluster together for protection,
assistance, or resource access. Regularly Arranged Slide 26 26
Community Structure Slide 27 27 COMMUNITIES IN TRANSITION
Ecological Succession Primary Succession - A community begins to
develop on a site previously unoccupied by living organisms. -
Pioneer Species Secondary Succession - An existing community is
disrupted and a new one subsequently develops at the site. -
Ecological Development Slide 28 28 Primary Succession Slide 29 29
Ecological Succession Climax Community - Community that develops
and seemingly resists further change. Individualistic Community -
Species become established according to their ability to colonize
and reproduce in a given area. Slide 30 30
