INTERSEXUAL RESOURCE PARTITIONING IN BLACK-TAILED DEER - A TEST OF THE BODY-SIZE HYPOTHESIS

To understand deer-habitat interactions important to making management decisions, it is necessary to ask questions in an evolutionary framew ork. Then, patterns that are detected can be evaluated in terms of how they potentially influence fitness, and to make more accurate predict ions about changes in habitat use with changes in the environment. Int ersexual resource partitioning in Odocoileus spp. is considered to be affected by sexual dimorphism in body size. Body size influences metab olic requirements which in turn presumably influence feeding behavior. Thus, I tested 5 predictions with black-tailed deer (0. hemionus colu mbianus) on Hopland Field Station, Mendocino County, California, 1989- 91, to determine if body size and its presumed impact on feeding behav ior cause intersexual resource partitioning. Predictions, tested using radio telemetry and by measuring feeding behaviors of free ranging an imals, ranged from general expectations about spatial distribution to specific predictions about feeding behavior. Males had larger (P < 0.0 01) home-range sizes than females, except in summer. Based on body siz e considerations female home ranges should be 0.75 the size of males. Mean ratios mostly varied from 0. 30 to 0.40. However, because of larg e variation, confidence intervals overlapped 0.75 during most seasons. Females exhibited a higher (P < 0.05) degree of site fidelity among s easons than males. The sexes differed (P < 0.001) in use of habitats a mong months, however, the pattern was not consistent. Generally, deer used more open habitats (grassland, chaparral grassland, and oak grass land habitats) in the wetter winter months, and more closed habitats ( oak woodland, chaparral) in the drier summer months. There was conside rable monthly variation in percent of time active (P = 0.004) but no d ifferences (P = 0.59) between the sexes. Type of forage and percent of time a deer's head was in the feeding position were the only variable s correlated (P < 0.001) with number of bites taken in 7- to 10-minute feeding sessions. Type of forage accounted for 92% of the variation a ssociated with number of bites. No differences were detected between t he sexes in number of bites taken (P = 0.34) or percent of time head w as in the feeding position (P = 0.39) on any forage type. There was no (P > 0.42) relationship between incisor breadth and body mass for eac h sex. Deer on Hopland Field Station exhibit sexual segregation, but t he reason they segregate cannot be explained by differences in body si ze that may impact feeding behavior. The sexes do not partition resour ces to reduce intersexual competition. Harvest programs that assume no resource partitioning, however, ignore the possibility of intrasexual density dependent effects being manifested because of individuals avo iding the opposite sex or grouping with their own sex.