Oral Presentation- Symposium 12th International Mammalogical Congress

All bark and no bite? Impacts of recolonising gray wolves on sympatric prey are primarily non-consumptive in a managed landscape of western North America (#488)

Justin A Dellinger 1 , Aaron J Wirsing 2 , Michael R Heithaus 3 , William J Ripple 4
  1. Wildlife Investigations Lab, California Department of Fish and Wildlife, Rancho Cordova, CA, USA
  2. School of Environmental and Forest Sciences, University of Washington, Seattle, WA, USA
  3. Department of Biological Sciences, Florida International University, North Miami, FL, USA
  4. Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR, USA

Apex predators are increasingly recognised for the top-down impacts they can trigger by consuming and intimidating prey. These ecosystem effects have largely been demonstrated in wilderness and protected areas, however, raising questions about the extent to which they manifest in human-dominated landscapes. Accordingly, we took advantage of ongoing gray wolf (Canis lupus) recolonisation of a human-influenced region of the state of Washington, USA, to examine the impacts of these canid predators on survival and behavior of two sympatric prey species, mule deer (Odocoileus hemionus) and white-tailed deer (O. virginianus). Analysing data from GPS-collared deer (61 mule and 59 white-tailed deer) collected at four study sites (two with wolf packs and two wolf-free areas) over a period of four years (2012-2016), we found that the presence of wolves had little impact on survival in either prey species. Indeed, wolves inflicted only two mortalities over the course of our investigation; humans (recreational hunters) were instead the chief source of mortality. By contrast, both deer species responded behaviorally to the risk of predation, with mule deer exhibiting large-scale spatial shifts that reduced overlap with wolves and white-tailed deer manifesting fine-scale shifts to gentle terrain that facilitated their means of escape post-encounter (fleeing). Our results add to a growing literature suggesting that the effects of top predators may be dampened in human-dominated systems. They also suggest, however, that non-consumptive effects of these species (e.g., costly defensive adjustments by prey) may be more resilient to human presence than those stemming from direct predation.