In the face of environmental stressors, change is imperative for species to remain in place. The nature and degree of this change is of great interest, as it sheds light into the ways in which species respond to ecological and habitat change and may continue to respond during periods of more frequent and severe change brought on by increasing levels of anthropogenic activity. I set out to uncover the ways in which species respond in-situ to environmental change using geometric morphometric analysis (GMA) and stable isotope analysis (SIA) for a suite of 10 small-mammals, across time and space in the Great Basin, USA. GMA provides a quantitative way to assess size and shape dynamics, while SIA records a snapshot of species’ resource usage, and thus gives an estimate of diet. Together these two metrics provide insight into two different strategies species can use to remain in place. Morphological change often has evolutionary underpinnings, while dietary flexibility is more likely to reflect a plastic response due to changes in behavior. How these different axes of change buffer species, as well as the relationship of these axes to one another across space and time, is unexplored. This thesis addresses this gap and provides context to how a variety of small mammals spanning phylogenetic histories, dietary strategies and body sizes have responded to environmental change temporally and spatially. Furthermore, I explore the feasibility of using space for time substitutions, and whether or not intra- and interspecific variation across space today, is comparable to the range of variation that a species could exhibit through time.
I found that species, more often than not, have responded individualistically across space and time both morphologically and isotopically. Even the same species at different localities appear to have responded to selective pressures in unique ways. I found that temporally, species show a strong correlation between morphological variation and dietary flexibility (Chapter 2), indicating that these two axes of variation are working together to buffer species through time. Conversely, I found that spatial trends did not mirror those seen through time, and species’ axes of variation were weakly correlated or de-coupled, suggesting that flexibility of one axis was enough to buffer species across space. Across both fossil and modern environmental gradients, dietary flexibility and morphological variation can change quickly, over decadal to centennial time-scales or possibly even quicker and are both important in buffering species against ecological change, even if the axes are not actually changing synchronously. Lastly, spatial variation does not appear to be a good representative of temporal variation, isotopically, but may be applicable to morphological variation. Specifically, species today exhibit greater levels of dietary flexibility than in the past, indicating a greater reliance on dietary flexibility as a means of environmental buffering in the Modern. This is contrasted by Modern morphological variation consistent with the fossil record. Together these set the stage for investigating new questions such as: does dietary flexibility precede morphological shape change, and are the increased levels of dietary flexibility observed today sustainable into the future
