How predator incursions affect critical patch size: The role of the functional response

Understanding the impact of habitat edges provides a key to deciphering how community dynamics change as functions of habitat structure and spatial sc ale. Motivated by studies of predation on bird nests in forest fragments an d other cases of "crossboundary subsidies," we present results from a parti al differential equation model in which a patch-resident prey species suffe rs incidental mortality from a generalist predator species residing in the surrounding matrix habitat. We demonstrate that predator intrusions have th e potential to induce critical patch size effects for the prey species, eve n when the prey's dynamics would otherwise preclude such effects. We also d emonstrate that the existence of critical patch size effects depends on the functional response of the predator, with Lotka-Volterra and Type II funct ional responses generating the effect (but not Type III). We conclude by di scussing how predator-induced critical patch size effects can influence opp ortunities for region wide persistence of the prey by altering the fraction and spatial distribution of meaningful patches within a metapopulation.