Unit 3: Introduction to Communities

Community

An association of interacting species inhabiting some defined area. 

Community Ecology

The study of collective properties in the structure of multi-species biological assemblages.

What are the three issues in community definitions?

Co-Occurence; Recurrence; Communities tend toward dynamic stability.

Co-Occurrence

Species must coexist.

Recurrence

Same groups of species recur all the time.

Communities tend toward dynamic stability.

Communities should tend towards dynamic stability. 

Individualistic School

Co-Occurrence; abstract of continuously varying vegetation; collection of populations with similar environmental requirements.

Superorganism School

Tightly coevolved in evolutionary time; important in ecological time; prevailing thought.

How does species richness relate to latitudes? 

Higher species richness at lower latitudes (near the equator). 

Time Theory Hypothesis

Rate of evolution higher in tropics than in temperate zone.

Competition Hypothesis

Stability-time; time for evolution to occur uninterrupted is higher (more stable climate).

Colonization Hypothesis

Rate of colonization, not rate of evolution, is limiting in temperate zone.

Climate Stability Hypothesis

Tropics are less seasonal than temperate zone.

Spatial Heterogeneity Hypothesis

Spatial (Architectural) heterogeneity.

Predation Hypothesis

Greater species-specific predation in tropics.

Productivity Hypothesis

Productivity; supports more levels of the food web; does’t make much sense.