USING SPATIALLY EXPLICIT MODELS TO CHARACTERIZE FORAGING PERFORMANCE IN HETEROGENEOUS LANDSCAPES

The success of most foragers is constrained by limits to their sensory perception, memory, and locomotion. However, a general and quantitati ve understanding of how these constraints affect foraging benefits, an d the trade-offs they imply for foraging strategies, is difficult to a chieve. This article develops foraging performance statistics to asses s constraints and define trade-offs for foragers using biased random w alk behaviors, a widespread class of foraging strategies that includes area-restricted searches, kineses, and taxes. The statistics are expe cted payoff and expected travel time and assess two components of fora ging performance: how effectively foragers distinguish between resourc e-poor and resource rich parts of their environments and how quickly f oragers in poor parts of the environment locate resource concentration s. These statistics provide a link between mechanistic models of indiv iduals' movement and functional responses, population-level models of forager distributions in space and time, and foraging theory predictio ns of optimal forager distributions and criteria fur abandoning resour ce parches. Application of the analysis to area-restricted search in c occinellid beetles suggests that the most essential aspect of these pr edators' foraging strategy is the ''turning threshold,'' the prey dens ity at which ladybirds switch from slow to rapid turning. This thresho ld effectively determines whether a forager exploits or abandons a res ource concentration. Foraging is most effective when the threshold is tuned to match physiological or energetic requirements. These performa nce statistics also help anticipate and interpret the dynamics of comp lex spatially and temporally varying forager-resource systems.