Friends and foes in foraging: intraspecific interactions act on foraging-cycle stages

Abstract

Intraspecific interactions may increase or decrease foraging rates of individual consumers, and such facilitation or interference interactions should affect individual foraging economies as well as predator-prey processes at the population level. To mechanistically predict individual foraging performance, we need to investigate the effects of positive and negative interactions on separate foraging-cycle stages. We illustrate the importance and viability of examining the effects of facilitation and interference on different foraging-cycle stages using three piscivore species as a model system. We studied individual foraging behaviour when alone or in the presence of conspecifics, and show that northern pike foraging in the presence of conspecifics decrease attack frequencies and consumption rates, although no explicit agonistic behaviours were recorded. Pikeperch increase consumption rates in conspecific groups, possibly through a prey-mediated increase in capture success, as pikeperch showed no direct behavioural interactions. The actively cooperating Eurasian perch increase capture success and consumption rates in groups. The results demonstrate the need to combine behavioural studies of positive and negative effects of intraspecific interactions on foraging-cycle stages with quantifications of overall consumption rates. Pure behavioural observations may result in misinterpretations of the effects of interactions on foraging, while studies on consumption rates only would lack the mechanistic base of the obtained results. We also suggest that effects of intraspecific interactions during the foraging cycle should be incorporated in mechanistic models of facilitation and interference to elucidate the link between individual behaviours and higher-order processes.