Date of Award

Fall 12-2021

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)


Hamish Greig

Second Committee Member

Amanda Klemmer

Third Committee Member

Michael Kinnison

Additional Committee Members

Jacquelyn Gill

Bradley Taylor


As the global climate changes, many species are shifting their geographic ranges, often towards the poles or upslope in elevation. The ubiquity of these observation has renewed discussions about the mechanisms that determine species’ range margins. Leading hypotheses state abiotic variables should be the most important factor for setting range limits in environmentally stressful habitats. However, I propose an alternative hypothesis that biotic interactions may still be critically important for setting range limits, even in abiotically stressful habitats. Using a model system of ponds in the Rocky Mountains of Colorado, I developed several field experiments to empirically test the role of biotic interactions, including competition and predation, for setting range limits at across regional elevational gradients and among local habitats. First, I conducted a field experiment spanning an elevational gradient (2800 – 3400 m a.s.l.) to show that biotic interactions can indeed play important roles in maintaining range limits in abiotically stressful habitats. Second, using a field experiment examining a more localized hydroperiod gradient, I show that predation can facilitate the coexistence of competing resident and range-shifting species further supporting the importance of species interactions for maintaining range limits. Third, I show that long-term patterns in species persistence at their range margins are not always correlated with pair-wise interactions, suggesting the importance of considering the entire suite of interactions a species encounters in the ecological communities at their range margins. Finally, I propose a new framework for considering species interactions and range margins in a changing climate. This framework takes a whole food-web approach and integrates the effects of abiotic variables like temperature on the population demographics of and interactions between members of ecological communities. Together these studies highlight the importance of considering both abiotic variables and biotic interactions together if we are to truly understand the effects of climate change on species’ geographic distribution