lecture 19

What is species sorting (filtering)?

The process by which dispersal, abiotic conditions, and biotic interactions determine which species occur in a community.

Resource partitioning model

• assumptions-

  • Species differ in resource use and compete for limited resources

• Coexistence-

  • Species divide resources (niches), reducing competition.

• MacArthur showed niche differences in warblers; Tilman showed species coexist by using different resources.

What are the assumptions of the intermediate disturbance hypothesis?

Disturbance varies in frequency/intensity and affects competition.

How does intermediate disturbance promote coexistence?

It prevents competitive exclusion while allowing some species to persist.

What did Sousa’s study show?

Species diversity is highest at intermediate levels of disturbance.

What do lottery and neutral models assume?

Species are functionally similar and have equal competitive ability.

How does coexistence occur in lottery/neutral models?

Chance events and random recruitment determine which species persist.

What did Sale’s study test?

That recruitment of reef fish is random, supporting lottery/neutral processes.

Does one coexistence model apply to all communities?

No, applicability depends on environmental context.

What is community function?

Ecosystem processes like productivity, nutrient cycling, and stability.

What did Tilman’s studies show about diversity and function?

Higher species diversity increases productivity and stability.

What is the complementary hypothesis?

Species use resources differently, increasing overall function with diversity.

What is the redundancy hypothesis?

Many species have similar roles, so function increases then levels off.

What is the idiosyncratic hypothesis?

Community function depends on which specific species are present.

How do the three hypotheses differ in their predictions?

• Complementary: linear increase

• Redundancy: increase then plateau

• Idiosyncratic: variable, depends on species identity