Habitat Interference by Exotic Axis Deer (Axis axis) on Native White-tailed Deer (Odocoileus virginianus) in Texas

Abstract

Exotic ruminants were introduced into Texas with little knowledge of how the species would interact with native white-tailed deer (Odocoileus virgimanus). Axis deer (Axis axis), the most common exotic ungulate in the state, are larger and more gregarious than white-tailed deer, and there is overlap in resources used by both species. In this study, I tested if the presence of axis deer affected habitat selection of white-tailed deer by comparing habitat use of white-tailed deer in an area where axis deer were present and then after axis deer were removed (temporal control) to another area where only white-tailed deer were present (spatial control). I wanted to assess if axis deer and white-tailed deer could coexist via each species being superior m a different form of competition (interference or exploitative). Vehicle surveys were conducted to determine locations of white-tailed deer and axis deer over two survey season. The data were used to evaluate possible changes in habitat selection by white-tailed deer after the removal of axis deer. I also observed animals at artificial feeding sites that were provisioned with a high quality food. At feeding sites I recorded aggressive behaviors and the amount of time each species spent at feeders alone and together. From these data I determined dominance relationships between species and estimated the amount of time each species spent at feeders alone and together. The treatment area contained 53.85% wooded habitat. White-tailed deer used wooded habitat 34.6 ± 4.2% during the first survey season and 79.7 ± 4.5 % in the second survey season, suggesting that the removal of axis deer influenced the habitat selection of white-tailed deer. No changes were observed in habitat selection of white-tailed deer in the control area (34.31 % wooded) during the two survey seasons (23.1 ± 3.6% in the first survey season and 25.1 ± 3.1 in the second survey season). Axis deer were dominant to white-tailed deer at the artificial feeding sites. Although marginally significant, both species spent a significantly greater amount of time alone than at feeders together. However, the amount of time that individuals of each species spent at feeders did not differ. These results suggest that axis deer are superior at interference competition, but white-tailed deer were not superior at exploitative competition, thus the conditions for coexistence are not met. Currently, populations of axis deer in Texas may be at manageable densities. However, increases in axis deer population sizes have the potential to displace white-tailed deer over large spatial scales which may result in a subsequent decrease m their numbers.