SNOWSHOE HARE DYNAMICS AT THEIR SOUTHERN RANGE BOUNDARY: CYCLIC EROSION AND ISLAND PERSISTENCE

Abstract

Global climate change has shifted seasonality, influencing species across multiple scales, from individual traits to community dynamics. I examined these effects on a winter-adapted mammal snowshoe hare (Lepus americanus) at its southern range boundary, a region expected to be vulnerable to climate change. Specifically, I investigated how southern range populations are responding to changing environmental conditions. I examined this across two distinct ecological scales. At the community scale, a 40-year analysis of mainland populations (44º–49ºN) in the Great Lakes region revealed a clear gradient of fading cyclicity, indicating widespread population destabilization likely driven by pressures from shifting seasonality. Additionally, I assessed a hypothesized refugium on Isle Royale National Park. At the population and individual scale, this island population was found to be large, connected, demographically stable, and cyclic, despite lacking the specialized predators thought essential for cycle stability. These results demonstrate how shifting seasonality drives both cyclic collapse and unique persistence at the southern range edge. By integrating analyses across scales from community-wide cycle dynamics to localized refugial stability, I examined both broad scale regional shifts as well as identified Isle Royale as a critical stronghold for the persistence of this climate-vulnerable species.