The effect of patch depletion on meal patterns in rats

Abstract

Abstract. Animals exploiting patchily-distributed resources must decide when to leave a given patch and seek another. If economically based, this decision will depend on the rate of return in the patch, the cost of moving to a new patch, and the overall rate of return in the environment. This study examined how these economic considerations may influence the pattern of daily food intake, i.e. the meal pattern. Laboratory rats lived continuously in a simulated depleting-patch environment in which the cost of beginning a meal in a new patch was controlled by a fixed-ratio price of access to the feeder and the rate of patch depletion was controlled with progressive-ratio schedules of pellet cost. As predicted by a cost-minimizing model, patch leaving was a joint function of the size of the progressive ratio and the size of the access cost: meals were smaller at higher depletion rates, but larger at higher access costs. However, meals were somewhat larger than the size that would have minimized feeding time and reliably larger than the size that would have minimized response output. Furthermore, although meal frequency changed in the opposite directions from meal size, the changes were not entirely compensatory; daily intake and body weight declined in the higher-cost conditions. These results suggest that intake patterns are the result of compromises between economic and physiological requirements.