Complexity Increases Predictability in Allometrically-Constrained Food Webs

All ecosystems are subjected to chronic disturbances such as harvest, pollution, and climate change. The capacity to forecast how species respond to such press perturbations is limited by our imprecise knowledge of pairwise species interaction strengths and the many direct and indirect pathways along which perturbations can propagate between species. Network complexity has thereby been seen to limit the predictability of ecological systems. Here we challenge this notion by demonstrating how the influence of indirect effects declines with network complexity when species interactions are governed by universal allometric constraints. These constraints affect a positive relationship between network connectance and the prevalence of weak interactions that limit disturbance propagation in large networks. This relationship preserves predictability even when pairwise interaction strengths exhibit substantial variation or uncertainty. Thus, although strongly interacting species drive disturbance responses, it is the array of weak interactions that controls the consistency of these responses.