Geographical Body Size Clines in Sika Deer: Path Analysis to Discern Amongst Environmental Influences

Abstract

Using Japanese sika deer from boreal and subtropical forests, we investigated the effects of environmental factors on body size variation and tested the following ecological hypotheses pertaining to Bergmann’s rule in mammals: (1) heat conservation, (2) heat dissipation, (3) starvation resistance, (4) food availability and (5) insularity. Data on body sizes and habitats of sika deer from 31 populations on the Japanese archipelago were collected. Body mass and cranial greatest length (CGL; reflecting skeletal body size) were measured and analysed separately among gender groups. Path analyses were used to clarify inter-variable relationships and estimate direct and indirect effects of environmental variables on body size. Consistent with Bergmann’s rule, a clear latitudinal cline of body size was found for sika deer. Subsequent path analyses showed that the abiotic factors, specifically mean annual temperature and annual precipitation, had significant negative effects on body size, and annual temperature had the greatest effect among tested environmental variables. Winter severity and food availability during spring were significantly associated with body mass but not with CGL. Both heat conservation and dissipation hypotheses were accepted and food availability and starvation resistance hypotheses were applicable to variation of body mass but not to CGL, indicating that phenotypic changes in fat reserves strongly influence variation in body mass. Path diagram modelling of inter-variable relationships fit well for females but not for males, and unexplained variation of male body size suggested the presence of unidentified factors. Variation in mating systems among populations may effect body size variation of the male sika deer.