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RESPONSE OF TWO LOW-DENSITY POPULATIONS OF PEROMYSCUS LEUCOPUS TO INCREASED FOOD AVAILABILITY

Abstract Studies of food supplementation in small mammals often result in significant increases in population density. These numerical responses to increased food availability may interact with other variables, such as predation, territoriality, and emigration, to limit population size. In this study, the demography of Peromyscus leucopus was compared between an oak wood undergoing a high mast year and a reference wood. At a smaller spatial scale, replicated plots were supplemented with rodent chow in an attempt to reproduce patterns occurring at the larger woodlot scale. Some of the food supplemented plots also had predators excluded to test for interactions between top–down and bottom–up effects. Very low-densities of P. leucopus responded numerically to increased food availability. Results for a relatively large “natural” experiment and a more controlled manipulative experiment were similar. In both cases, the increase in numbers was primarily the result of immigration, not reproduction. Increased food availability in the spring resulted in earlier reproduction but a decline in numbers—probably because of territorial defense. The food supplementation led to increased predator activity and decreased survivorship of the prey. This resulted in a rapid turnover of individuals and a significant predator × food interaction.