The effect of intraspecific interference on Kogotus nonus (Plecoptera) foraging behaviour

With significant mutual interference between predators, a trade off between the benefit of foraging in high density prey patches and the cost of sharing those patches with other predators is expected. These costs and benefits were assessed for a stonefly predator, Kogotus nonus Needham and Claassen, and its mayfly prey, Baetis tricaudatus Dodds, by varying prey and predator densities in small artificial streams. Solitary predators showed a functional response produced by changes in encounter rate and modified by changes in time spent moving by the predator. Intensity of behavioural interference between predators was high, but did not change significantly as a function of prey density. The experimentally determined costs and benefits were used to calculate the optimal predator distribution in terms of foraging success, given contagiously distributed prey. When predators were assumed to interfere with each other, a random predator distribution was predicted to be optimal, and this was consistent with the observed distribution of Kogotus nonus in the field.