Community Ecology

Communitygroup of populations interacting with one

another within the same environment.

Example: fallen log with all species that live within it.

Species diversity increases the closer you get to the equator.

Composition of a community – list of species

Diversity of a community – includes number of species and their abundance

Community models Individualistic Model: HL Gleason

Each population in a community is there because its basic needs are met (abiotic)

Boundaries between communities are not distinct

Interactive model – FE Clements Predicts the same species will recur in communities whose

boundaries are distinct from one another, species dependent on biotic interactions

Community structure is dependent on both abiotic and biotic factors

Island biogeographySize of an island and its distance from a

population source affects species diversity.

When immigration and extinction rates are equal, an equilibrium in species diversity develops.

Structure of the community

Habitat – place where an organism lives and reproduces

Ecological niche – role it plays in its community, including habitat and interactions with organismsFundamental niche – all conditions under which

the organism can potentially survive and reproduce

Realized niche – set of conditions under which it exists in nature.Competition forces an organism to occupy its realized

niche, which is smaller than fundamental

CompetitionInterspecific competition – members of

different species try to use a resource that is limited.May result in resource partitioning leading to niche

specialization.

Competitive exclusion principle – no two species can indefinitely occupy the same niche at the same time

Predator-prey Predation – when a predator feeds on prey

In nature, the presence of predators can decrease prey densities and vice versa

Prey defenses Camouflage – ability to blend into a background

Walking sticks, katydids Mimicry – when a species resembles another that

possesses an antipredator defenseBatesian – mimic that lacks the defenseMullerian – mimics that share the same protective

defense

Symbiotic relationships3 types: parasitism, commensalism and

mutualism

Parasitism: parasite derives nourishment from another, a host. Parasites can weaken or kill host, +, -

Commensalism – between two species in which one species is benefited and the other is neither benefited nor harmed, +, 0

Mutualism – both members of association benefit, +,+ Mycorrhizae

Community DevelopmentEcological succession – change involving a

series of species replacements in a community following a disturbance.End result can not be predicted

Pioneer species – first species to begin secondary succession

Community BiodiversityIntermediate disturbance hypothesis –

moderate amounts of disturbances at moderate frequency are required for a high degree of community diversity. Ex. Fire

Keystone species – organisms that play a great role in maintaining the function and diversity of an ecosystem than would be predicted by their abundance.