Adaptive foraging and the rewiring of size-structured food webs following extinctions

Abstract Over the past decade, attempts have been made to characterise the factors affecting the robustness of food webs. Many studies have been carried out using a “topological” approach, in which secondary extinctions in ecological networks are determined by the structure of the network alone. These studies have led to numerous insights; for example how robustness is highly dependent on the order of extinctions, the fraction of basal species, as well as the connectance of the webs. But there has been criticism of these investigations for their lack of biological realism, such as the inability of species to alter their diets when species are lost, or the reliance on the criterion that a species only suffers a secondary extinction once it loses all its resources. Here, building on past approaches, we address these issues by introducing allometric optimal foraging theory to explore the consequences of species adaptively responding (by altering feeding links) to loss of prey in size-structured food webs. We also explore the effect on robustness of a secondary extinction criterion based on a threshold of energy loss, rather than merely the absence of a connection to at least one prey. We show that both rewiring and energetic extinction criteria greatly affect the robustness of model food webs, and that these new factors interact with each other as well as with the body mass distribution of the community, to shape the complexity–robustness relationship.