Wolf-Beaver Dynamics in a Southern Boreal Ecosystem

Abstract

Predator-prey relationships can have wide-ranging ecological and landscape-level effects. Knowledge of these relationships is therefore crucial for understanding how changes in predator-prey communities affect ecosystems. Throughout much of the circumpolar boreal ecosystem, wolves are significant predators of beavers and beavers important prey for wolves, yet wolf-beaver dynamics remain poorly understood. My objective was to shed light on this predator-prey dynamic by studying wolf-beaver interactions in the Greater Voyageurs Ecosystem (GVE), a southern boreal ecosystem in Northern Minnesota. Specifically, I wanted to understand where and how wolves hunt beavers, what impact wolf predation has on beaver populations, and how wolf predation on beavers might impact ecosystem function. By searching 11,817 GPS-clusters from 24 GPS-collared wolves during 2015-2019, I documented 748 instances where wolves attempted to ambush beavers and 214 instances where wolves killed beavers. Through this, I determined wolves are able to ambush beavers by anticipating the movements and behavior of beavers due to a fundamental understanding of beavers’ sensory abilities. Further, wolves can strategically select ambushing locations by simultaneously accounting for abiotic and biotic factors, ultimately allowing wolves to counter beaver’s defenses and exploit this unique prey. The extent to which wolves influence beaver population change has been debated for decades despite a complete lack of quantitative data on the subject. I estimated, by determining kill and predation rates, that wolf packs can remove 38-42% of the beaver population in their territory in a year. Yet, in high-density beaver populations such as the GVE, predation pressure appears to have little influence on beaver population dynamics because beaver populations can quickly compensate for predation. Though wolves may not alter beaver population size, I demonstrate how wolves alter wetland creation and recolonization by killing dispersing beavers. By studying beaver pond creation and recolonization patterns, I determined that 84% of newly created and recolonized beaver ponds in the GVE remained occupied until the fall, whereas 0% remained active after a wolf killed the dispersing beaver that colonized that pond. By affecting where and when beavers engineer ecosystems, wolves alter all of the ecological processes that occur due to beaver-created impoundments.