Community Ecology

1. Community Ecology

2. Community • group 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

3. 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

4. Island biogeography • Size 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.

5. 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 organisms • Fundamental 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

6. Competition • Interspecific 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

7. 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 defense • Batesian – mimic that lacks the defense • Mullerian – mimics that share the same protective defense

8. Symbiotic relationships • 3 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

9. Community Development • Ecological 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

10. Community Biodiversity • Intermediate 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.