Impacts of Re-colonizing Gray Wolves on Mule Deer and White-tailed Deer in North-Central Washington

Impacts of Re-colonizing Gray Wolves on Mule Deer and White-tailed Deer in North-Central Washington Justin Aaron Dellinger Chair of the Supervisory Committee: Assistant Professor Aaron J. Wirsing School of Environmental and Forest Sciences Previous research on gray wolves (Canis lupus) in protected landscapes demonstrates these large carnivores can have consumptive and non-consumptive effects on prey species which lead to top-down trophic cascades. However, much remains to be known about impacts of gray wolves on prey in managed landscapes as well as how these predators influence interactions between prey species. Recent natural re-colonization of gray wolves to managed landscapes of Washington state facilitated a natural experiment wherein we explored impacts of gray wolves on multiple sympatric prey species – mule deer (Odocoileus hemionus) and white-tailed deer (O. virginianus). We compared survival, habitat use, and resource partitioning of adult mule deer and adult white-tailed deer in wolf present and wolf absent areas. Mule deer and white-tailed deer survival rates were not negatively impacted by presence of gray wolves. Season was the primary factor in explaining all predator and human-caused mortality. Our data suggests gray wolves may not have consumptive effects on native prey populations in Washington state. Next, mule deer and white-tailed deer experiencing gray wolf predation risk did exhibit shifts in habitat use relative to conspecifics in areas without gray wolves. Shifts in habitat use by mule deer and white-tailed occurred at coarse and fine-spatial scales, respectively, and were explained by divergent escape tactics of each prey species and the landscape features that promote escape of each deer species when facing gray wolf predation risk. It appears gray wolves can influence habitat use of multiple prey species and potentially at differing spatial scales depending on escape behavior of prey species and the landscape features that promote escape of prey from predation. Our results suggest gray wolves could initiate multiple top-down trophic cascades via prey species specific shifts in habitat use in response to gray wolf predation risk. Lastly, there was increased resource partitioning between mule deer and white-tailed deer in areas with gray wolves compared to resource partitioning between mule deer and white-tailed deer in areas without gray wolves. Increased resource partitioning between mule deer and white-tailed deer was again explained by divergent escape tactics of each prey species and the landscape features promoting escape of each deer species subject to wolf predation risk. However, direction and magnitude of resource partitioning between mule deer and white-tailed in areas with gray wolves compared to areas without gray wolves varied with season and scale. Our findings demonstrate that gray wolf predation risk can mediate interactions between co-occurring prey species but is context-dependent. We suggest further research on consumptive and non-consumptive effects of gray wolves on multiple prey species to better understand the potential for top-down trophic cascades in managed landscapes.