Community Ecology
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
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 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.
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
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
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
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
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
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.