Emergent Allee Effects through Biomass Overcompensation

Abstract

This chapter discusses the emergence of a positive feedback between the density of predators and the availability of its food, mediated through biomass overcompensation in the prey life history stage that it forages on. This positive feedback between predation, prey availability, and thus predator population growth rate manifests itself at the population-level as an Allee effect for the predator: a predator population at low density will decline to extinction, whereas at high densities predators will manage to establish themselves in a community with prey. However, this positive relation between predator density and its population growth rate does not result from any positively density-dependent interactions among the predators themselves, which generally form the basis of an Allee effect. Instead, predators only interact with each other through exploitative competition for prey. The Allee effect emerges solely as a consequence of the demographic changes in the prey population, which are induced by the mortality that the predator imposes. For this reason this phenomenon is referred to as an “emergent Allee effect.”