Significance of memory properties in prey choice decisions

To forage efficiently in a spatially and temporally heterogeneous environme nt requires that an individual's information from the immediate past is com bined with information from the more distant past to track environmental ch ange. We made use of a model involving exponentially devaluating weights fo r past events to emulate behaviour of the individual's memory. As the deval uation rate increases, more weight is given to the most recent events. Firs t, performance of individuals with different memory properties was tested i n simulations in which two prey types with different profitabilities were a vailable in different proportions. In a structurally stable prey environmen t a low memory devaluation rate gave better estimation of prey proportions than a high memory devaluation rate. In a highly variable environment, on t he contrary, individuals with high devaluation rate could more quickly corr ect their estimates as prey availability changed, although this was achieve d with the cost of high error rate of the estimate. Second. the ability to reliably assess relative abundances of the prey types proved to increase an individual's success in prey choice (according to the decision rules by th e optimal prey choice model). Third, in further simulations individuals wer e allowed to adjust their memory devaluation rate according to experience f rom their success in prey choice decisions in previous patches. We found th at there was no need to adjust a high devaluation memory in a highly variab le environment, but foragers starting with low devaluation value rather rap idly shifted to high devaluation rates. In a relatively stable environment the situation was reversed and finally all foragers used low devaluation ra tes. These results imply that the variation in estimation efficacy of prey availability may be critical in terms of optimal prey choice and thus memor y properties should be included in examinations of prey choice. Including i ndividual variation in foraging performance in individual-based models coul d increase our understanding of the consequences of these differences at th e population and community levels. (C) 1999 Elsevier Science B.V. All light s reserved.