Chapter 53 ~ Community Ecology

Community structure

Community ~ an assemblage of populations living close enough together for potential interaction

Richness (number of species) & abundance…….

Species diversity

Hypotheses: •Individualistic ~ chance assemblage with similar abiotic requirements •Interactive ~ assemblage locked into association by mandatory biotic interactions

Interactions

Interspecific (interactions between populations of different species within a community): •Predation including parasitism; may involve a keystone species/predator •Competition •Commensalism •Mutualism

Predation defense

Cryptic (camouflage) coloration

Aposematic (warning) coloration

Mimicry ~ superficial resemblance to another species √ Batesian ~ palatable/ harmless species mimics an unpalatable/ harmful model √ Mullerian ~ 2 or more unpalatable, aposematically colored species resemble each other

Competition: a closer look

Interference ~ actual fighting over resources

Exploitative ~ consumption or use of similar resources

Competitive Exclusion Principle (Lotka / Volterra)~ 2 species with similar needs for the same limiting resources cannot coexist in the same place √Gause experiment

Competition evidence

Resource partitioning ~ sympatric species consume slightly different foods or use other resources in slightly different ways

Character displacement ~ sympatric species tend to diverge in those characteristics that overlap

The Niche

Ecological niche ~ the sum total of an organism’s use of biotic and abiotic resources in its environment; its “ecological role” √ fundamental ~ the set of resources a population is theoretically capable of using under ideal conditions √ realized ~ the resources a population actually uses

Thus, 2 species cannot coexist in a community if their niches are identical

Summary: interactions in communities

Intraspecific competition: same species

Exploitative (each organism seeks resources)

Can lead to size fluctuations

Larvae and adults have different needs

Density can limit development (not enough food)

Higher density à smaller, less fertile adults

Causes emigration

Interference (contests, fighting)

Dominance hierarchies/social position

Contests are frequently non-combative

“winner” eats, mates first à increases fitness of group

territoriality

Summary: interactions

Interspecific competition: different species

Principle of competitive exclusion

Competition causes specialization

Local extinction

Range restriction

Predation

Adaptations to catch prey/escape

Speed, coloration, thorns, poisons, mimicry, vigilance (herds and schools)

Symbiosis

Parasitism

Mutualism

Commensalism

Succession

Ecological succession ~ transition in species composition over ecological time

Primary ~ begun in lifeless area; no soil, perhaps volcanic activity or retreating glacier

Secondary ~ an existing community has been cleared by some disturbance that leaves the soil intact

Succession 2

Early arrivals may facilitate, inhibit, or tolerate later species.

Facilitate: make the environment more suitable for later species

Inhibit: make the environment less suitable