Multiple Predator Effects

Numerous studies have argued that the dynamics of species within food webs are poorly predicted by summing pairwise interactions between each species. Such deviations in the observed effect of multiple species operating concurrently that differ from the expected effect of pairwise interactions are known as higher-order interactions. Understanding the prevalence of higher-order interactions and the degree to which they modify community dynamics is critical to advancing community ecology from a field that has largely focused on phenomena description to one that emphasizes prediction. To date, most studies of higher order interactions have focused on describing the existence of higher order interactions using species modules (e.g., two predators and one prey). While such studies have emphasized the importance of both predator antagonism and synergy as extant phenomena in simplified communities, the degree to which higher-order interactions permeate in more complex food webs that contain diverse predator and prey assemblages remains poorly understood. For over 30 years ecologists have studied predator-predator interactions including cooperation, competition, and intraguild predation to gain greater insight into the role of predators in affecting the structure and function of ecosystems. Our understanding of the importance and prevalence of predator-predator interactions in driving ecological communities is, however, only as good as the methods we use to statistically test for these interactions. Here, we describe challenges and possible bias associated with traditional experimental design and statistical approaches that are driven by the heavy depletion of prey throughout experiments. We offer an analytical solution to studies where extensive prey depletion occurs and also provide suggestions for how empiricists can design experiments to limit bias associated with depletion. Our study has important implications for our understanding of how predator diversity affects ecosystem structure and function. Such effects of predator diversity are critical to understand, because species that are higher on the food chain often suffer greater effects from activities such as harvesting, habitat fragmentation, toxin bioaccumulation, and habitat degradation.

This paper is led by: Mike McCoy (Eastern Carolina University) and coauthored by Craig Osenberg and Adrian Stier (me). Our work was generously funded by the National Science Foundation.

McCoy M.W., Stier A.C., and C.W. Osenberg. 2012. Emergent effects of multiple predators on prey survival. The importance of depletion and the functional response. Ecology Letters. 15: 1449-1456. PDF