Optimal searching behaviour: the value of sampling information

Computer simulations were used to investigate how the efficiency of area-restricted search is influenced by the extent of past sampling experience used by large grazers to assess food quality. Areas encompassed by fixed numbers of the most recently visited sampling units were referred to as reference windows. Past sampling information gained over various reference windows dictated searching decisions. Indeed, simulated animals compared the profitability of the current food patch with the average profitability of the food encountered over various reference windows before deciding whether an extensive searching mode (ESM) or an intensive searching mode (ISM) should be adopted to search for the next food patch. The model was parameterised based on the habitat and foraging behaviour of bison (Bison bison L.) to insure the use of parameter values that could reflect natural situations. My simulations indicate that searching efficiency, as measured from the average profitability of the 350 food patches encountered during a foraging bout (kJ/min . sampling event), increased in a decelerating fashion with the expansion of the reference window, and levelled off sooner with greater environmental stochasticity. Past sampling information had lower value in environments where the spatial distribution of food was less predictable. An increase in the ability of finding similar food types when in an ISM and different food types when in an ESM led to higher searching efficiency, a plateau that started with larger reference windows, and an increase in the value of sampling information. In most cases, the increase in searching efficiency levelled off with the consideration of more than 120 units sampling units, representing a reference window of only 30 m(2) for bison. A faulty assumption of systematic search when foragers use area-restricted search can lead to biases from conventional foraging theories, particularly for animals highly efficient during ISM and foraging in environments with high spatial auto-correlation in distribution of food types. My study emphasises that reliable predictions about resource use requires considering the interaction between searching behaviour and habitat structure, together with the reference window used by animals to assess food quality. (C) 2002 Elsevier Science B.V. All rights reserved.