A Comparative Study of Resource Partitioning between Ochrotomys nuttalli and Peromyscus leucopus

Abstract

Resource utilization was examined in captivity for two coexisting small mammal species, the golden mouse ( Ochrotomys nuttalli ) and the white-footed mouse ( Peromyscus leucopus ). Bioenergetics, thermoregulation, and food-selection behavior were studied in terms of behavioral and physiological responses to different experimental conditions. Food consumption was measured to assess ingestion, egestion, assimilation, and respiration in laboratory-maintained mice at 10°C and 20°C. Ingestion rates increased at the lower ambient temperature in both species. Assimilated energy and, consequently, respiration were higher in Peromyscus than in Ochrotomys at both ambient temperatures. Body temperature was monitored every 12 h during a 5-day period in mice maintained at 10° and 20°C; studies were conducted both with and without nesting material. Ochrotomys consistently exhibited lower mean body temperatures than Peromyscus . Body temperatures in both species were significantly higher at the lower ambient temperature (10°C). Both species appear able to use behavioral adjustment of insulation (e.g., nest construction) to retard heat loss. Feeding preferences were analyzed by presenting individuals of each species a diversity of natural foods. Dietary diversity (H′) and evenness (e) were higher in Ochrotomys , indicating more equal apportionment among food items. Electivity values (I) indicated a preference of both species for blackberry and cherry fruits and a lack of preference for sumac. Differences in size of cheek pouches may contribute to the behavioral differences observed between species. Physiological and behavioral strategies illustrate the importance of energy requirements in determining species interactions and community structure.