The functional form of specialized predation dramatically affects whether Janzen-Connell effects can prevent competitive exclusion

Abstract

Janzen Connell Effects (JCEs), specialized predation of seeds and seedlings near conspecific trees, are hypothesized to promote high species richness. While past modeling studies show JCEs can maintain higher diversity than a neutral community, recent theoretical work indicates JCEs may weakly inhibit competitive exclusion when species exhibit interspecific fitness variation. However, recent models make somewhat restrictive assumptions about the functional form of specialized predation - that JCEs occur at a fixed rate when seeds/seedlings are within a fixed distance of a conspecific tree. Using a theoretical model, I show that the functional form of JCEs largely impacts their ability to promote coexistence. If specialized predation pressure increases additively with adult tree density and decays exponentially with distance, JCEs maintain considerably higher diversity than predicted by recent models. Parameterizing the model with values from a Panamanian tree community indicates JCEs can maintain high diversity in communities exhibiting high interspecific fitness variation.