Simulation of patch use by monkeys using operant conditioning

Food patch use by Japanese monkeys was examined using an operant conditioning procedure. Modified progressive ratio schedules, in which the probability of reinforcement decreases exponentially with the number of bar presses, were presented to 2 Japanese monkeys. Two types of schedule were used in each experimental session. One represented high quality food patches, where the probability of reinforcement was twice as high as in the other, which represented low quality food patches. The number of bar presses in each food patch was counted. Monkeys responded more frequently in high quality patches. The probability of reinforcement for the last response in each patch was the same in both types of schedule. The number of responses increased with a decrease in the occurrence of high quality patches, and with an increase in the inter-patch time interval. These results are in agreement with the predictions of Charnov’s marginal value theorem (Charnov, 1976). The pattern of patch use by monkeys observed in this study is discussed in terms of optimal foraging strategy.