Data on white-tailed deer (Odocoileus virginianus) body size and population density have been collected for several decades at Fort Hood, Texas. Habitat quality related to vegetation composition differs at the fort in two areas, West Fort Hood (WFH) and the West Region (WR). In other parts of its range, white-tailed deer decrease in size with a decline in food availability; however, the decrease tends to be in body mass, not skeletal stature. Body mass in both sexes and buck antler size should be significantly smaller in WFH where high quality deer habitat is proportionally less abundant than in WR, but these size measures vary with animal condition by season and year. If a difference in body mass and antler size occurs in conjunction with a difference in skeletal size, then differences reflect not only short term change but longer-term variability in ontogenetic growth rate between the two areas. This may be a product of phenotypic responses to food availability and/or genetic responses to geographic barriers to gene flow. The astragalus, which we measure in this study, grows to roughly 6 months of age; as a result variability in its size reflects generational (longer term) differences in ontogenetic growth rate.
Results/Conclusions
There are significant differences in body mass among bucks and does from WFH and WR, and these differences occur during two periods—the early 1990s and 2004 to 2008. Antler size significantly differs in several buck age classes. Astragalus size between the areas (2004 to 2008 only) does not significantly differ though on average for all measurements buck and doe size is smaller in WFH than WR. Population density is thought to be relatively high in WFH, and these data are based on spotlight surveys that attempt to control for differences in open habitat (visibility) between WFH and WR, the latter of which is proportionally high in areas with cover. The proportional abundance of Graminoid-dominant habitat and Juniperus-dominant habitat relative to deciduous-dominant habitat is high in WFH suggesting that food available for ontogenetic growth is lower in WFH. The higher proportional abundance of relatively open Graminioid-dominant habitat in WFH may also explain higher population-density estimates in that area. Recent theoretical and empirical studies highlight that animal body size and other variables correlate to food availability at large geospatial scales. The distribution of food can be expected to drive variability in intraspecific body size at local, regional, and greater geographic scales.
