12. Community Ecology

Community

a group of populations of

different species that live close enough to

one another to interact

Interspecific interactions

interactions

between individuals of different species

• Defined by the effects the interaction has

on the organisms involved

Intraspecific interactions

interactions

between members of the same species

Parasitism

+/- relationship in which the

parasite derives nutrition from its host

which is harmed in the process

• Parasite typically lives in/on host

Predation

+/- interaction in which one species eats another typically resulting

in the death of prey

Herbivory

+/- interaction in which an animal eats a photosynthetic organism—

may or may not result in death of prey

Interspecific competition

a -/- interaction between individuals of different

species competing for shared resources

Ecological niche

the sum of a species’ use of its biotic and abiotic environment

• E.g. food, shelter, water, nesting resources

Resource partitioning

differentiation of niches in response to interspecific

competition that results in limitation of competition for shared resources

• e.g. warblers foraging at different portions of tree

Fundamental niche

the full suite of resources potentially used by a species in

absence of competition

Realized niche

the portion of a species’ fundamental niche actually used in the

presence of competition

Commensalism

a +/0 relationship between two species in which one benefits

while the other is unaffected

Mutualisms

+/+ relationships in which individuals from both species benefit

• E.g. Acacia drepanolobium and symbiotic ant species in African savanna

Keystone species

A. Strong control over other species occurrence,

location, or density in communities/ecosystems

• B. Control via their niche

• C. Disproportionately large impact on ecosystem

relative to number/biomass of individuals present

Ecosystem engineers

A. Control community/ecosystem structure

• B. Control via directly altering their physical

landscape such that the availability of some

resources is changed

• C. Physical alteration is not simply through their

own growth

Trophic cascades

effects of higher trophic level trickle

down to lower levels

• predators limit the density/behavior of their prey  thus

enhance survival of next lower trophic leve