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Community Ecology
Campbell & ReeceChapter 54
a group of populations of different species living close enough to interact
Community
interactions with individuals of other species
includes: Competition Predation Herbivory Symbiosis Facilitation
Interspecific Interactions
interspecific competition is a +/- interaction that occurs when individuals of different species compete for a resource that limits their growth & survival
Competition
grown separately, both show logistic growth
when compete Paramecium caudatum became extinct in the culture
2 species competing for same limiting resource: 1 will have advantage in either using resources or in reproduction
Competitive Exclusion
is the sum of a species’ use of the biotic & abiotic resources in its environment
Eugene Odem: “If an organism’s habitat is its “address”, then niche is the organism’s “profession,”
Ecological Niche
not just where an organism lives but also what it eats, when it eats, who eats it, how many resources it uses, how much & what type of wastes it produces, what its parasites are, etc
Niche
3 birds live in spruce tree: each lives in different level so there is no competition even though all live in same trees
Niches: Resource Partitioning
closely related species may have populations that are sometimes allopatric (geographically separate) & sometimes sympatric (geographically overlapping)
Character Displacement
allopatric populations will be morphologically more similar & use similar resources
sympatric populations more likely to show differences in body structures & in the resources they use
Character Displacement
refers to the +/- interaction between species in which 1 species, the predator, kills & eats the other, the prey
Predation
acute senses claws, teeth, fangs, stingers, or
poison those that have to chase their prey
have adaptations that make them fast & agile
those that lie in ambush have adaptations that disguise their position
Feeding Adaptations of Predators
hiding, fleeing, forming herds or schools
active self-defense less common except for mothers protecting young (especially in larger, grazing mammals)
alarm calls mob the predator
Adaptations of Prey
Cryptic Coloration
Defensive Coloration in Animals
Camouflage makes prey difficult to
see
warning coloration often used by
animals that have effective chemical defenses
Aposematic Coloration
Defensive Coloration in Animals
Batesian mimicry: a palatable or harmless species mimics an unpalatable or harmful one
Defensive Coloration in Animals
Mullerian mimicry: 2 or more unpalatable species resemble each other; the more unpalatable prey there are the more quickly predators learn to avoid anything that resembles them
Defensive Coloration in Animals
refers to a +/- interaction in which an organism eats parts of a plant or alga
most herbivores are invertebrates specialized adaptations:
some insect have sensors on feet to detect toxins, or to detect nutritious & less nutritious plants
Herbivory
feature toxins, spines, thorns some toxins:
Strychnine: produced by tropical vine Nicotine: tobacco Tanins: variety of plants Selenium: found in “locoweeds” because
sheep & cattle that eat them found wandering aimlessly, some die
Plant Adaptations
produce chemicals their predators find distasteful: Cinnamon Cloves Peppermint
Plant Adaptations
when 2 or more species live in direct & intimate contact w/each other
some: helpful, harmful, or neutral
Symbiosis
Ecologists estimate that 1/3 of all species are parasites
many have complex life cycles requiring multiple hosts
some change behavior of their host to increase probability of it being transferred
Parasites
leads their crustacean host to leave shelter increasing chances it will be eaten by a bird, its next host
Parasitic accanthcephalan
a +/- symbiotic interaction in which 1 organism, the parasite, derives its nourishment from another organism, its host, which is harmed in the process
Endoparasites: live w/in body of their host ex: tapeworm
Ectoparasites: feed on external surface of their host ex: ticks, lice
Parasitism
small wasps that lay their eggs in living hosts that feed on the body, killing it
Parasitoid Insects
an interspecific interaction that benefits both species, +/+
Acacia trees & stinging ants: ants feed on nectar & protein-rich
swellings on tree tree protected by thorns (ants live
inside) & stinging ants that attack any herbivores & ants clip vegetation that grows near the tree
Mutualism
Mutualism
an interaction between species that benefits one of the species but neither harms nor helps the other +/0
in reality may have some slight + or - affect
Commensalism
species can have +/+ or +/0 effects on the survival or reproduction of other species w/out living in direct, intimate contact with each other
this type of interaction = facilitation common in plant ecology
Facilitation
Black rush increases # of plant species that can live in upper middle zone of salt marshes
variety of different kinds of organisms that make up a community
Species richness: # of different species in community
Relative abundance: proportion each species represents of all individuals in community
Species Diversity
Which is Which?
Ecologists use different tools to compare the diversity of different communities over time & space.
Shannon diversity is an index of diversity based on species richness & abundance
Shannon Diversity
Shannon diversity = H
ni = # of 1 species n = # of all species In = natural
logarithm
Shannon Diversity
Which Forest is More Diverse?
higher diversity communities generally are more productive & better able to withstand & recover from environmental stresses
Diversity & Community Stability
higher diversity communities more resistant to effects of invasive species
Invasive Species
layers in food chains/ pyramids
Trophic Structure
summary of trophic relationships of a community
tells whom eats whom
Food Webs
Why are they short?1. Energetic Hypothesis
length limited by inefficiency of nrg transfer
2. Dynamic Stability Hypothesis longer food chains less stable population fluctuations @ lower trophic
levels magnified @ higher levels
Limits of Food Chain Length
the more abundant species in a community
are highly competitive
Dominant Species
1 way to measure effect is to study what happens when a dominant species is removed:
ex: tree, American Chestnut was dominant tree in deciduous forests before 1910
fungal disease chestnut blight introduced: killed almost all of them didn’t bother maples, beeches, oak, or hickories, or birds, or mammals, but 7 species of moths & butterflies became extinct
Dominant Species
not usually abundant in community exert strong control by their pivotal
ecological role or niche
Keystone Species
species that dramatically alter their physical environment
aka: foundation species effect on other species can be + or –
depending on needs of other species
Ecosystem Engineers
proposes a unidirectional influence from lower to higher trophic levels presence or absence of mineral nutrients
(N) controls plant (V) #s which in turn controls herbivore (H) #s which in turn controls predator (P) #s
N V H P adding or removing #s of P will not effect
lower trophic levels but adding or removing N will affect biomass of all higher trophic levels
Bottom-Up Model
postulates #s of predators mainly controls community organization because predators limit herbivores, herbivores limit etc: N V H P aka: trophic cascade model used to improve water quality in
polluted lakes (approach called biomanipulation)
Top-Down Model
an event (storm, flood, fire, drought, overgrazing, or human activity) that changes a community by removing organisms from it or altering resource availability
Disturbance
evidence suggests that disturbance & lack of equilibrium not stability & equilibrium, are the norm for most communities
Nonequilibrium Model
type of disturbance, their frequency & severity vary among communities’
high level of disturbance is generally the result of a high intensity & high frequency disturbance
Characterizing Disturbance
says moderate levels of disturbance can foster higher species diversity than can low or high levels of disturbance
Intermediate Disturbance Hypothesis
the sequence of community & ecosystem changes after a disturbance
Primary Succession: type of ecological succession that occurs in an area where there were originally no organisms present & where soil has not yet formed
Ecological Succession
Primary Succession
type of succession that occurs where an existing community has been cleared by some disturbance that leaves the soil or substrate intact
Secondary Succession
early arrival species may facilitate the arrival of late arriving species by making environment more hospitible
sometimes the early species inhibit establishment of later species so the later species succeeds in spite of the presence of early species
early species may be completely independent of later species which tolerate conditions created by early species
Succession
humans are the most widespread agents of disturbance
man‘s effects usually reduce species diversity
humans also interfere with natural disturbances like fires which can be important disturbances to some communities
Human Disturbance
large-scale factors that influence the diversity of communities
Biogeographic Factors
species richness generally declines along a latitudinal gradient from the tropics the poles
tropics are much older which may contribute to species richness but it is also affected by climate (amt heat, sunlight, water)
Latitudinal Gradients
the biodiversity pattern that shows that the larger the geographic area of a community is, the more species it has
Species-Area Curve
Species richness of North American trees increases most predictably with actual evapotranspiration (evaporation of water from soil + transpiration of water from plants) which is a function of solar radiation, temp, & water availability
Energy, Water, & Species Richness
explanation for this phenomena: the larger areas offer greater diversity if habitats & microhabitats
Species-Area Curve
are generally isolated, limited size so ideal for studying biogeographic factors that affect biodiversity
“islands” = oceanic islands + habitat islands ex: mountain tops Lakes woodland fragments
Island Equilibrium Model
Immigration & Extinction Rates: equilibrium # of species on an island
represents a balance between the immigration of new species & extinction of established species
Island Equilibrium Model
Effect of Island Size: larger islands may ultimately have a
larger equilibrium # of species than smaller islands because immigration rates tend to be higher & extinction rates lower on larger islands
Island Equilibrium Model
Near islands tend to have larger equilibrium #s of species than far islands because immigration rates to near islands are higher & extinction rates are lower
Island Equilibrium Model
are disease causing microorganisms Viruses infectious RNA molecules: viroids infectious RNA proteins: prions
Pathogens
can quickly & extensively alter community structure especially when introduced into new
habitats new hosts have not had chance to
become resistant thru natural selection
Pathogens
pathogens transferred from other animals humans
cause of largest class of emerging human disease
community ecology provides framework for identification of key species interactions ass’c with such pathogens & for helping us track & control their spread
Zoonotic Pathogens
can be transferred by direct contact thru intermediate species called a
vector
Zoonotic Pathogens
often parasites Ticks Lice Mosquitoes
Vectors
