Behavioral Responses to Climate Change in Chipmunks of the Sierra Nevada

Anthropogenic climate change is drastically affecting the lives of animals across the planet, leading many of them to shift their ranges to higher latitudes or elevations. As their environments and habitats are modified, how individual organisms respond to novel conditions and situations will have critical implications for shaping population and species level responses to environmental change. Characterizing both individual behavioral responses to novelty and population-level patterns of demography and life history should provide us with important information elucidating the processes through which organisms are responding to climate change.Chipmunks (Genus: Tamias) in the central Sierra Nevada Mountains of California provide an ideal system for exploring these themes. Over the past century, the alpine chipmunk (T. alpinus) has – in apparent response to changing environmental conditions -- experienced a significant upward contraction of its elevational range. In contrast, the partially sympatric lodgepole chipmunk (T. speciosus) has undergone no detectable change in elevational distribution during this period. As part of understanding these differences in response, it is critical to examine potential interspecific differences in behavioral response to novelty and to quantify population-level differences in demography that may contribute to the contrasting patterns of range response documented for these animals. For my first chapter, I examine how individual responses to novelty may inform population-level responses to climate change. Two aspects of behavior that are often used to assess interactions with new environments are exploration and boldness, each of which is expected to influence adaptively important outcomes such as discovery of novel resources. These behavioral attributes may be influenced by degree of ecological specialization, with more specialized species typically thought to display a reduced tendency to interact with novel habitats. To test this prediction, I used open-field assays to compare exploratory behavior and boldness among free-living members of the two focal species of chipmunks. My analyses reveal that while individual T. speciosus tend to be bolder and to display greater overall activity than individual T. alpinus, measures of exploratory behavior do not differ between species. These findings have important implications for understanding reported differences in the elevational responses of these species to changing environmental conditions in the Sierra Nevada. More generally, these analyses underscore the 2 potential importance of individual-level differences in behavior in shaping higher-level patterns of response to environmental change. For my second chapter, I examine how demographic traits vary between my two focal species, as a first step toward determining if such traits can explain population-level patterns of range shifts in response to climate change. Anthropogenic climate change is causing many species to shift their range in response to warming temperatures. However, the demographic mechanisms that drive these changes remain poorly understood. To test the prediction that species with contracting ranges will exhibit demographic vital rates associated with population decline, I analyzed the results of a multi-year mark recapture study of our two focal species. My analyses reveal that sex ratio and reproductive output vary little between species, while body condition varies significantly in both species across localities and capture years, and recapture rate differ significantly, with T. alpinus tending to have lower body condition and a lower likelihood to be captured from one year to the next. However, these analyses also reveal that much of the variation detected can be explained by local, site level effects. These results emphasize that in ecologically similar species, even subtle differences in local demographic response may drive long term population dynamics under environmental change. For my third chapter, I provide the first characterization of the repeatability of individual behavioral responses to novelty in the two focal study species. Repeatability of behavioral responses, often referred to as animal “personality,” is thought to be critical in allowing natural selection to shape these aspects of behavior. Accordingly, quantitative estimates of the repeatability offer important insights into the causes and consequences of individual variation in behavior. Using repeated testing of individual free-living alpine and lodgepole chipmunks, I assess the repeatability of the measures of exploration and boldness examined in Chapter 1 and I examine potential correlations between these behavioral responses to determine if, together, they represent a potential behavioral syndrome. Although sample sizes were limited due to the challenges of working with free-living animals, my analyses suggest that exploration is more repeatable than boldness. I found no significant correlation between these behavioral responses, suggesting that they are not linked as part of a single syndrome. Collectively, these findings raise important questions regarding the nature and implications of repeatability in individual behavioral responses to novelty.

Advisor: Lacey, Eileen A