Linking physiology and biogeography: Disentangling the constraints on the distributions of ant species

Understanding the factors that limit the distribution of species is at the core of ecological and biogeographical research, and is critical if we are to predict the responses of key ecosystem components to ongoing climatic changes. My doctoral research seeks to provide an understanding of how thermal physiology influences species’ distributions and better define the mechanisms underlying geographic variation in biodiversity. By using natural temperature gradients (both elevational and latitudinal) and coupling controlled laboratory experiments with field observations and null modeling approaches, I was able to document the role of inter-specific variation in thermal physiology and, more interesting, inter-population variation in thermal physiology, in shaping the distribution of diversity on a warming planet. I determined that species’ density and distributions are shaped by both biotic and abiotic factors, but that the influence of these factors is geographically-dependent. I further examined the role of temperature by determining how different rates of warming affect thermal physiology and might provide insight into separate aspects of an organism’s life history and its accompanying coping mechanisms. Finally, I used a common garden experiment and phylogenetic analyses to determine to what extent ecological and evolutionary forces play a role in shaping the thermal niche. I found patterns suggestive of local adaptation and no evidence for lab acclimation, suggesting that some species may have limited acclimation ability and therefore will be more susceptible to climate warming. This dissertation suggests that variation in thermal physiology within and among species is important in understanding the factors that shape diversity and how species will be distributed now, and in the future.