Evaluation of Competitive Moose-Beaver Herbivory on Isle Royale National Park

Abstract

Beavers (Castor canadensis) play a key role in creating aquatic habitat and sustaining aquatic biodiversity in freshwater ecosystems across North America, including in Isle Royale National Park (ISRO). The National Park Service (NPS) hypothesize that competitive pressure from moose (Alces alces) in ISRO will drive beavers to forage at greater distances from their lodges, which may place them at greater risk for predation and ultimately have negative implications for the park’s aquatic ecosystems. Determining whether this occurs in ISRO, and if so, the degree to which it occurs, is an important research goal for NPS. The objective of this study is to identify common foraging preferences for beavers and moose and to investigate whether competition from moose leads to changes in beaver foraging behavior. Using forest structure, beaver herbivory, and moose herbivory survey data provided by NPS, we developed a predictive model forecasting beaver foraging behavior in response to moose herbivory pressure. While the literature to date supports that distance and vegetation type influence beavers’ foraging preferences, our model results only found the effect of distance to water, but were inconclusive with respect to vegetation preferences and the impact of moose on beaver foraging. Output from our analysis was limited by the amount of available data, and the disjoint protocols, i.e., beaver and vegetation-moose data were collected at different locations. To better identify beaver preferences and any potential competitive effect from moose, we recommend that future data collection include vegetation transects that record both beaver and moose browse data and vegetation structure, i.e., available vegetation data.