Effects of predation on intraspecific aggregation of prey and prey diversity in a subtidal marine food web
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Abstract
The aggregation model of coexistence suggests that intraspecific aggregation in local patches decreases richness locally, but increases richness regionally. While this model has largely been applied to competing species, it may also apply to predator – prey systems if predators generate intraspecific aggregation in their prey. Predators may influence intraspecific aggregation in prey communities by affecting prey immigration, emigration, and survival (both directly through predation and indirectly by modifying prey interactions and behavior). We performed a field experiment to determine whether predators influence the aggregation of their macroinvertebrate prey, and whether prey aggregation influenced richness in a marine subtidal food web. We quantified prey colonization of eight treatments that differed in the composition and richness of predators. We found positive intraspecific aggregation of prey in all but one treatment. We then asked whether the observed patterns in intraspecific aggregation among prey generated by predators led to a decrease in local richness (alpha diversity), and an increase in species turnover between local patches (beta diversity), and regional richness (gamma diversity). We found that intraspecific aggregation did not affect alpha diversity, but did significantly influence beta and (marginally) gamma diversity. Our results add to a growing list of communities whose constituents are aggregated. Our results suggest that, in open systems with mobile prey, the effects of predators on the initial development of prey communities may contribute to regional richness, and this may occur even in the absence of predator and aggregation effects on local richness.
