Mixed encounters, limited perception and optimal foraging

This article demonstrates how perceptual constraints of predators and the p ossibility that predators encounter prey both sequentially (one prey type a t a time) and simultaneously (two or more prey types at a time) may influen ce the predator attack decisions, diet composition and functional response of a behavioural predator-prey system. Individuals of a predator species ar e assumed to forage optimally on two prey types and to have exact knowledge of prey population numbers (or densities) only in a neighbourhood of their actual spatial location. The system characteristics are inspected by means of a discrete-time, discrete-space, individual-based model of the one-pred ator-two-prey interaction. Model predictions are compared with ones that ha ve been obtained by assuming only sequential encounters of predators with p rey and/or omniscient predators aware of prey population densities in the w hole environment. It is shown that the zero-one prey choice rule, optimal f or sequential encounters and omniscient predators, shifts to abruptly chang ing partial preferences for both prey types in the case of omniscient preda tors faced with both types of prey encounters. The latter, in turn, become gradually changing partial preferences when predator omniscience is conside red only local. (C) 2000 Society for Mathematical Biology.