Central place foragers, prey depletion halos, and how behavioral niche partitioning promotes consumer coexistence

Abstract

Many seabirds congregate in large colonies for breeding, a time when they are central place foragers. An influential idea in seabird ecology posits that competition during breeding results in an area of reduced prey availability around colonies, a phenomenon known as Ashmoles halo, and that this limits colony size. This idea has gained empirical support, including the finding that species coexisting within a colony might be able to do so by foraging on a single prey species but at different distances. Here, we provide a comprehensive mathematical model for central place foragers exploiting a single prey in a two-dimensional environment, where the prey distribution is the result of intrinsic birth and death, movement in space and mortality due to foraging birds (we also consider a variant tailored toward colonial social insects). Bird predation at different distances occurs according to an ideal free foraging distribution that maximizes prey delivery under flight and search costs. We fully characterize the birds ideal free distribution and the prey distribution it generates. Our results show that prey depletion halos around breeding colonies are a robust phenomenon and that the birds ideal free distribution is sensitive to prey movement. Furthermore, coexistence of several seabird species on a single prey easily emerges through behavioral niche partitioning whenever trait differences between species entail trade-offs between efficiently exploiting a scarce prey close to the colony and a more abundant prey far away. Such behavioral-based coexistence-inducing mechanism should generalize to other habitat and diet choice scenarios. Significance statementThis study presents a mathematical model to explore the distribution of foraging trips among seabirds breeding on isolated islands, providing insight into the emergence of prey depletion halos around colonies. Our findings reveal that such halos are a robust feature of central place foraging, independent of prey dynamics. Additionally, the model shows that trait-mediated niche partitioning promotes coexistence among species through behavioral segregation into different circular zones around the island. This partitioning occurs despite a shared preference to forage close to the island, where flight costs are lowest. The study advances understanding of ecological coexistence mechanisms and suggests broader applicability to other predator-prey systems beyond seabird ecology, offering a new perspective on community assembly under shared preferences.