Differential resource use by endemic and expanding rodents on the tundra may allow coexistence in the face of climate change

Species abundances and range boundaries are shifting with climate change, creating novel species interactions that could alter competitive interactions, predator-prey dynamics, pathogen transmission, and plant-herbivore dynamics. Boreal forest species are expanding onto the Arctic tundra as longer growing seasons increase resource availability, while many Arctic species’ ranges are contracting. Meadow voles (Microtus pennsylvanicus Ord, 1815), a widespread generalist, recently expanded onto the tundra, resulting in novel interactions with collared lemmings (Dicrostonyx richardsoni Merriam, 1900), a key herbivore whose cyclic population fluctuations influence tundra community dynamics. To understand the potential competitive impact of range expansion by meadow voles on collared lemmings, we examined diets of lemmings and voles using stable isotope analysis of hair. Stable isotope mixing models indicated lemmings primarily consumed shrubs (75%) while voles mostly fed on graminoids and herbs (97%), with 19% overlap in isotopic niche space, indicating that lemmings and voles generally consume different resources. These results suggest expanding boreal and endemic Arctic rodents may co-exist by consuming different resources, with minimal impact on lemming population dynamics. Still, dietary overlap may change over time with changes in resource availability and population abundance. Furthermore, increased prey diversity could subsidize tundra predators during cyclic lemming lows and alter predation rates on endemic tundra species.