Community assembly

What are Diamond’s assembly rules?

• Interspecific competition generates assembly rules

• There are limits to similarity in a community

• Forbidden species combinations: some species never coexist due to competition → checkerboard distributions

• Resource availability can alter which species can coexist (large islands have more resources, and this determines which species have access to sufficient resources to support viable populations)

What is a regional species pool?

All the species that could potentially colonize a local site or community

What is a local species pool?

The species present in a local community

What are assembly rules?

• The rules that specify why only a limited subset of species in the regional pool are present in the local community

• Not able to predict which species are present in a community

What is a guild?

A group of species that exploit the same class of environmental resources in a similar way (hummingbirds and other nectar-feeding birds form a guild exploiting flowering plants)

What are Hutchinsonian ratios?

Reduced niche overlap reduces competition and allows species to coexist

What did McCloskey propose about patterns of co-occurrence?

• Observed communities use more of available resources

• Unobserved communities are unstable and allow the addition of new species

List 2 types of relationships between regional and local species pools

• Type 1: linear

• Type 2: saturating

What is the traditional view of community assembly?

A hierarchical series of filters:

• Dispersal

  • May limit which species reach a local community

  • Species may not be present because of physical barriers or because the dispersal event has not yet occurred

• Environmental filters: determine which traits are adaptive in a given environment and decrease the range of species traits observed in the local community

• Biotic filters: including competition, predation, parasitism, disease, and mutualisms

How does dispersal influence alpha diversity?

• Alpha diversity initially increases with dispersal

• As diversity increases above amax, alpha diversity declines, as best competitors at a regional scale come to dominate each local community

How does dispersal influence beta diversity?

• Beta diversity decreases as dispersal increases

• Communities become more similar in composition

What did Cadotte and Tucker argue about environmental filtering?

• The filter analogy and traditional view of community assembly is not valid

• Dispersal, environmental, and biotic interactions work in concert to determine community assembly

When should history matter to community assembly?

• Large regional species pool

• Low rate of dispersal/connectedness

• High primary productivity

• Low disturbance

How does regional species richness influence local species richness?

• The local species pool cannot exceed the richness of the regional pool

• Type I: linear

• Type II: saturating

What are metacommunities?

• A set of local communities linked by the dispersal of one or more of their constituent species

• Can incorporate changes into the regional species pool due to speciation, extinction, and introduction of new species by humans

What is alpha diversity?

Species richness within a local community

What is beta diversity?

Differences/turnover in species richness between local communities

What is a mass effect?

As dispersal increases, alpha diversity initially increases, as species that would have been competitively excluded are rescued by immigration from other local communities where they are better adapted