Predator behaviour and prey density: evaluating density‐dependent intraspecific interactions on predator functional responses

Abstract

In models of size‐structured predator–prey systems, the effects are evaluated of gape‐size limited predation on prey population growth and density when predators are non‐interacting, cannibalistic, interfering, and cannibalistic and interfering. Predation from non‐interacting predators markedly reduces prey density, compared with prey densities in the absence of predation. When density‐dependent cannibalism between predators is introduced, predator density and therefore total functional response decrease, resulting in a decrease in predation pressure and higher prey densities. Size‐ and density‐dependent interference between predators substantially decreases functional responses in the predators, and the prey population is thus allowed to grow more dense. Allowing for cannibalism between interfering predators also decreases predator density, but here the decreased number of predators does not have the releasing effect seen in solely cannibalistic predators. The interference between predators decreases with predator density, and per capita functional responses increase and compensate for the decrease in predator density. These theoretical results are compared with results from natural systems with pikeperch and northern pike. Both species are cannibalistic, and pike are also kleptoparasitic, mirroring the models. Results from introductions of the different piscivores into natural systems corroborate the outcome of the models, since introduction or increased densities of pikeperch have shown to have severe and long‐lasting effects on prey, while pike have only initial, decreasing over time effects on prey stock. Thus, predator behaviour may seriously affect predator impact on prey, and size‐ and density‐dependent interactions between predators may be a major key to the understanding of predator–prey dynamics and community composition in lakes.