Spatial trophic cascades in communities connected by dispersal and foraging

Abstract

Pairwise interactions between species have indirect consequences that reverberate throughout the whole ecosystem. In particular, interaction effects may propagate in a spatial dimension, to localities connected by organismal movement. Here we study the propagation of interactions with a spatially explicit metacommunity model, where local sites are connected by dispersal, foraging, or by both types of movement. We show that direct and net effects of pairwise interactions may differ in sign when foraging across localities is prevalent. Further, the effect of a species over another in the local community does not necessarily correspond to its effect at the metacommunity scale; this correspondence is again mediated by the type of movement across localities. Networks of net effects are fully connected, indicating that every species in the metacommunity has a non-zero influence on every other species. Lastly, the magnitude of net effects between any two species strongly decays with the distance between them. These theoretical results strengthen the importance of considering indirect effects across species at both the local and regional scale, point to the differences between types of movement across locations, and thus open novel avenues for the study of interaction effects in spatially explicit settings.