Dietary niche overlap in an understudied Mustelidae community in the subboreal forests of western North America: does body size differentiate dietary niche?

Understanding the many ways closely related species are adapted to coexist is fundamental for maintaining biologically diverse ecological communities. We used carbon (C) and nitrogen (N) stable isotopes of hair and nail tissue to quantify overlap in dietary niche among American mink (Neogale vison von Schreber, 1776), American marten (Martes americana Turton, 1806), short-tailed weasel (Mustela erminea Linnaeus, 1758), and North American river otter (Lontra canadensis Schreber, 1777), and to quantify seasonal variation in diet among mink and marten. We collected tissue samples from the four species between 2015 and 2017 across an 18,000 km² area in central British Columbia, Canada. We hypothesised that the dietary niche breadth of the mustelid species would scale with body size. Standard ellipses suggested that mink had the broadest dietary niche and the only one that overlapped with all other species. Among marten, there was evidence of shifts in diet resulting from seasonal changes in the consumption of vertebrate prey. Marten and weasel occupied approximately the same isotopic space and their niches were contained fully within that of mink. Our results suggested that the coexistence of mink, marten, weasel, and river otter was driven in part by dietary niche partitioning. Differences in realized niche along spatial or temporal resource axes may have further contributed to preventing competitive exclusion among these closely related species. Although dietary analyses can provide insights on some components of interspecific competition, future investigations should include measures of spatial and temporal overlap in resource use.