Direct and indirect effects of wolves on interior Alaska's mesopredator community

Abstract

Large carnivores may indirectly benefit small predators by suppressing competitively dominant mesopredators. However, our current understanding of interactions within the carnivore guild does not account for carrion subsidies provided by large carnivores, which could facilitate mesopredators during times of prey scarcity. This could be particularly relevant in northern ecosystems characterized by long harsh winters and decadal prey cycling. In Alaska, state-sponsored wolf (Canis lupus) control programs reduce wolf populations by as much as 50-80% across 8 game management units that collectively total over 165,000 km2, yet the impact of this practice on the Alaska's diverse mesopredator community remains unknown. We used a quasi-experiment resulting from a wolf control program in the upper Susitna River Basin that was adjacent to Denali National Park and Preserve lands, where wolves occur at naturally regulated densities. From January-March 2013 and 2014, we collected coyote (Canis latrans) and red fox (Vulpes vulpes) scats and conducted snow track surveys for wolves, mesocarnivores, and their prey. I quantified the relative strengths of direct and indirect effects of wolves on 5 mesopredator species while accounting for snowpack characteristics and small mammal abundance, and assessed winter diet overlap and composition by coyotes and red foxes in response to wolves and small prey availability. My findings indicated that wolves could strongly influence mesocarnivore communities in the Denali and Susitna systems, however despite a strong effect of wolves on coyotes, there was no evidence to support a mesopredator release cascade mediated by coyotes. Rather, I observed a near guild-wide response to wolf presence, whereby mesopredators were positively associated with wolves within each study area. The relative strength of top down versus bottom up effects in this study system further indicated that during a period characterized by low small mammal abundance, wolves were the strongest predictor of canid and wolverine occurrence. Coyote and red fox diet further revealed that carrion was a heavily used resource during this time of low prey abundance, yet red foxes may minimize competition with coyotes for carrion by increasing their use of voles. Finally, I present a hypothesis that local scale facilitation by large carnivores could lead to landscape patterns of suppression by large carnivores, suggesting a key link between abundance patterns and the structure of carnivore communities at different spatial scales relevant to conservation and management.