A Size-Based Theory for Inferring Global Change Impacts on Food Web Structure

Global changes induce deep modifications in species distribution worldwide. However, the consequences of such changes on community structure are still poorly understood. Here, we propose a new framework, coupling species distribution and trophic models, to predict global change impacts on food-web structure. We first present a new method, inspired from the niche model of food web structure, to infer the matrix of potential interactions among a pool of species. The method applies to both local and regional scales. We find that this method gives robust predictions of the structure of food webs and that its efficiency is increased when the strength of the body–size relationship between predators and preys increases. We then study the consequences of this relationship on the body-size distribution at the biogeographic scale. We find that trophic interactions significantly impact individual species distribution, and ultimately the body-size structure of ecological communities. The theory is illustrated with applications to the Mediterranean Sea and Pacific coral reefs. Our study highlights large-scale impacts of global change on marine food-web structure with potential deep consequences on ecosystem functioning. However, these impacts will likely be highly heterogeneous in space, challenging our current understanding of global change impact on local marine ecosystems.