Background/Question/Methods
In addition to altering patterns of prey richness, top predators can alter the composition of local communities.  However, the extent to which these local predator effects scale up to influence patterns of regional prey diversity is unclear.  We develop a theoretical model based on the theory of island biogeography that explores the potential impacts of predators on local and regional diversity of prey metacommunities.

Results/Conclusions  

In the model, we assume that predator effects can be both deterministic, by altering the size of the pool of species that can persist with predators, and stochastic, by altering colonization/extinction dynamics. Predators can alter prey community structure deterministically by eliminating prey species from the regional species pool that are unable to coexist with predators.  In such cases, predators are expected to decrease alpha- and beta-diversity, resulting in the loss of regional prey species richness (hereafter gamma-diversity).  However, predators also alter stochastic colonization/extinction dynamics, reducing alpha-diversity, but simultaneously increasing beta-diversity.  That is, stochastic effects can buffer the effects of predators on gamma diversity by altering the partitioning of alpha- and beta-diversity.  Model simulations suggest that the scale-dependent effect of predators on alpha and gamma-diversity among prey varies with the spatial context of metacommunities and the magnitude of deterministic and stochastic predator effects.