PARENT SESSION
Oral Session # 99: Late-Breaking Newsworthy Presentations.
Presiding: E Preisser and G Larocque
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 205.
Wolves influence elk movements: Behavior shapes a trophic cascade in Yellowstone National Park.
FORTIN, DANIEL*,1, BEYER, HAWTHORNE1, BOYCE, MARK1, SMITH, DOUGLAS2, MAO, JULIE1, 1 University of Alberta, Edmonton, Alberta, Canada2 Yellowstone National Park, Mammoth, Wyoming, USA
ABSTRACT- A trophic cascade has recently been reported among wolves, elk and aspen on the northern winter range of Yellowstone National Park, but the mechanisms of indirect interactions within this food chain have yet to be established. We investigated whether the observed trophic cascade might have a behavioral basis by exploring environmental factors influencing the winter movements of 13 elk equipped with GPS-radiocollars. Paths of traveling elk were broken down into steps, which correspond to the straight-line segment between successive locations at 5-hour intervals. Each observed step was paired with 200 random steps having the same starting point, but differing in length and/or direction. Comparison between environmental characteristics of observed and random steps revealed that elk movements were influenced by multiple environmental features, such as the distance from roads, the presence of a cliff along the step, and the energy required to make that step. After accounting for the influence of these environmental factors, we additionally found that elk selected steps on the basis of the habitat type in which they ended. This influence of habitat locations on elk movements depended on the spatial distribution of wolves in the northern winter range of the park. In low wolf-use areas, the relative preference for step end point locations followed: aspen stands > open areas > conifer forest areas. As the risks of wolf encounter increased, elk's preference for aspen stands gradually decreased, and selection became strongest for steps ending in conifer forest areas under high risks of encountering wolves. Our study supports the hypothesis that the Yellowstone's trophic cascade in the wolf-elk-aspen system has a behavioral basis, where elk respond to wolf spatial distribution on their winter range by shifting their habitat selection.
Key words: elk-wolf interactions, animal movement, trophic cascade, aspen