The motivation of my dissertation research was to understand the influence of climate and biotic factors on range limits with a focus on winter-adapted species, including the Canada lynx (Lynx canadensis), American marten (Martes americana), and snowshoe hare (Lepus americanus). I investigated range dynamics along the boreal-temperate ecotone of the northeastern US. Through an integrative literature review, I developed a theoretical framework building from existing thinking on range limits and ecological theory. I used this theory for my second chapter to evaluate direct and indirect causes of carnivore range limits in the northeastern US, using data collected from 6 years (2014–2019) of fieldwork. My third chapter again used this theory and classical understanding of density-dependence to evaluate factors influencing snowshoe hare populations along their trailing edge in the northeastern US. Finally, for my fourth chapter, I used the model outputs from the second chapter to compare current and future distributions based on causal and correlational frameworks given projected changes in snowpack and forest biomass.