Communities

Goals

1. To understand how species interact within biotic communities, and the evolutionary outcomes of these interactions

2. To understand the patterns of community diversity and what causes them

3. To become familiar with the ways that communities change over time during succession

Outline

How do populations within a community interact?

There are close interspecific interactions that are important to populations

these can result in coevolution: when 2 species adapt to each other (mutual, reciprocal evolution)

(+/-) predation, parasitism, herbivory

adaptations of predator pops to predation:

strategies: ambush, pursuit

life-dinner principle

adaptations of prey pops to predation:

• escape
• mechanical adaptations -- shells, spines, etc.
• flocking
• cryptic coloration
• warning coloration & noxiousness
  • mimicry (Batesian and Mullerian)

adaptations of plants to herbivory

• mechanical adaptations -- spines, etc. (mainly against vertebrates)
• secondary compounds (mainly against insects)

(-/-) Competition

When two species rely on similar limiting resources (= interspecific competition)

2 possible outcomes of competition over long time span

1. competitive exclusion: where resource use overlaps completely, and the better competitor outcompetes the worse. Competitive exclusion principle: complete competitors cannot coexist
2. resource partitioning: where there is incomplete overlap in resource use, and natural selection reduces the degree of competition. This can be seen in character displacement of former competitors

Species diversity

species richness vs. species evenness

factors that control diversity

competition (tends to lower spp richness)

predation can increase richness (keystone species)

keystone species -- e.g., elephants, fig trees, keystone predators

island/patch size

species diversity is controlled by mechanisms that are:

• complex
• poorly understood
• important

Succession

Primary succession -- in a new habitat

Secondary succession -- after a disturbance

early successional communities -- r strategists do well

late successional communities -- K strategists excell

Vocabulary

click here to go to community ecology vocabulary