Ecological and biogeographic patterns of muskrat and American mink

Abstract

Semiaquatic mammals are ecologically important to wetlands, but little is known about the extent of their ecological effects, their distribution patterns in human-influenced landscapes, and how morphological patterns vary on a continental scale. Muskrats (Ondatra zibethicus) and American mink (Neogale vison), a well-known predator of muskrats, co-occur in wetlands embedded in rapidly changing prairie ecosystems. First, muskrats have wide-ranging effects on wetland habitats and are sometimes considered ‘keystone species’ or ‘ecosystem engineers.’ To evaluate these claims, we conducted a thorough review of the scientific literature. Of 363 publications, only 6% explicitly considered muskrats to be ecosystem engineers (n = 9) or keystone species (n = 4). While muskrats have broad effects on wetland flora and fauna, studies investigating these effects generally occurred over small spatiotemporal scales and used dissimilar methods and reporting, which limited inference. On a broader spatial scale, we assessed how local- and landscape-scale variables affect spatial distributions of muskrat and mink. We used detection/non-detection data from 104 isolated wetlands in Kansas, USA, from 2019-2020. Wetland occupancy by muskrats was best predicted by local variables including higher emergent vegetation diversity, larger wetlands, and larger watersheds. Mink wetland occupancy was related to landscape-scale effects including greater prairie landcover, farther distances to the nearest adjacent wetland, and less woody vegetation. At the broadest spatial scales, semiaquatic mammals tend to be larger than terrestrial counterparts – a pattern that may reflect conformity to Bergmann’s rule. To test Bergmann’s rule for muskrat and American mink, we investigated latitudinal gradients in size across their native North American distribution. Using museum collections and data from state wildlife departments (n = 708 muskrat and n = 94 mink), we used AIC model selection to see if latitude best predicted changes in size for both species. We found support for Bergmann’s rule in muskrat, but not for mink. While no relationships between size and latitude were found for male mink, we did find support for the reverse pattern of Bergmann’s rule in female mink. Collectively, our findings contribute to a better understanding of semiaquatic mammal ecology across multiple scales.