The selective pressures acting on phenotypes are complex and can vary over space and time. To examine the effects of selection due to environmental conditions on avian bill morphology, we explored spatial and temporal variation in bill morphology in a common generalist songbird, the Dark-eyed Junco (Junco hyemalis). We measured bill length, width, and depth, and calculated surface area, for >800 museum specimens collected in the state of California from 1905-1980. We then examined which environmental variables (precipitation, temperature, and habitat type) at which temporal scales (seasonal, annual, hemi-decadal, and decadal) could explain variation in each measure of bill morphology. Although we predicted relationships consistent with selection on the bill for foraging utility and optimal thermoregulation, the patterns we found were more complex. The effects of the environmental factors examined varied with season and with the specific bill traits. Measures of habitat type were more strongly associated with bill morphology than were individual climate variables, and temperature was a more important predictor of bill morphology than precipitation. Bill surface area displayed stronger effects of environmental conditions than did linear measures of bill morphology. Of the climate variables identified as important in our analyses, support was strongest for the measure of decadal temperature variability. The strong relationship between vegetative community and bill surface area in our models, the support for longer-term temperature variables, and the support for the importance of temperature variability suggests that in complex natural systems, large-scale context—ecology and climate—plays a strong role that is not seen by looking at its component parts alone.

Different environmental conditions produce different selective pressures. We explored patterns of life history variation along an elevation gradient to identify the factors contributing to this variation. We monitored breeding Dark-eyed Juncos in the Sierra Nevada mountains of California at sites from 1960 to 2660 m above sea level and compared breeding season length, temporal patterns of peak breeding activity, clutch size, brood size, nestling quality, and nest mortality among elevations. We also compared maximum and minimum daily temperature, daily snow depth, and monthly precipitation across the elevations to determine whether these abiotic factors could explain life history variation. We found small differences in breeding season length and in the pattern of reproductive timing among elevations. While breeding season at the intermediate elevation was intermediate in length, the pattern of peak breeding activity was not intermediate between the patterns observed at low and high elevations. The life history differences across elevations could not be explained solely by abiotic factors, but may be related to the effects of those factors on the birds' prey base or nesting sites, potentially exacerbated at lower elevations by the ongoing drought. We found no differences among elevations in clutch size, brood size, or nestling quality. Higher elevations had greater nest mortality, possibly due to severe weather. A computer simulation constructed to mimic the field system suggests that these mortality differences, in combination with the differences in breeding season length, contribute to substantial differences among elevations in reproductive success which may be difficult to observe in a field setting.

We then investigated whether variation in climatic conditions, breeding season length, and number of offspring produced per season in populations of junco breeding at different elevations led to variation in breeding synchrony, in extra-pair paternity, or in the use of a sexually-selected male signal, the amount of white in the tail. We also tested for genetic structure among the populations. Using 12 variable microsatellite loci, we found differences in extra-pair paternity rates among our populations, with a low extra-pair paternity rate (20% of nests) at high elevations, a high rate (57%) at middle elevations, and an intermediate rate (38%) at low elevations. We found no differences among elevations in mean values of tail white or tail white asymmetry, and no differences in a measure of the honesty of the signal (the strength of the correlation between tail white and either of two indices of male quality). Despite differences in the temporal patterns of breeding activity as well as in the length of the breeding season, we found no differences in breeding synchrony among elevations, and no association between the presence of extra-pair paternity and a brood's breeding synchrony. We detected no genetic differentiation among populations, indicating that consistent gene flow occurs between the populations. Persistent gene flow may explain the lack of differentiation in the tail white signal despite substantial differences in the potential strength of sexual selection among elevations.

James L. Patton served as Curator of Mammals in the Museum of Vertebrate Zoology (MVZ) and as Professor of Integrative Biology (formerly Zoology) at the University of California, Berkeley, from January, 1969 until June, 2001. During his 32 years as a curator and a member of the Berkeley faculty, Jim made an indelible mark on vertebrate evolutionary biology through his tireless pursuit of excellence in research and teaching. In addition to significantly advancing studies of mammalian evolutionary genetics, systematics, and phylogeography, Jim was instrumental in shaping the careers of vertebrate biologists throughout the Americas. Given the magnitude of his impact on studies of mammals, it seemed only appropriate to celebrate Jim’s retirement from the Berkeley faculty by compiling a volume that reflects the breadth of his contributions to vertebrate biology. At the same time, everyone involved in the project agreed that the volume should capture something of Jim, the person. As those of us who have had the privilege of working with him know, Jim is an enthusiastic, generous, no-nonsense individual who doesn’t hesitate to support his students and colleagues in any way that he can. Thus, while Jim’s intellect and work ethic have made him a successful scientist, it is his personality that has endeared him to so many of his students and colleagues. Here, we try to capture both elements of Jim’s career. The result is a series of rigorous, original research papers combined with more informal recollections of Jim’s activities as a scholar, mentor, and museum curator. For those readers who have not had the opportunity to interact with Jim, we hope that the following pages will bring to life both the distinguished career and the distinctive personality of this highly respected evolutionary biologist.

An individual’s social environment can profoundly affect many aspects of their biology, including their behavior, reproductive success, physiology, and survival. Facultatively social species—those in which some individuals live in social groups while other individuals live solitarily—provide an important opportunity to explore the impact of variable social environments on conspecifics that experience similar ecological conditions. Uncovering the relative biological differences between individuals across alternative social environments is critical to the advancement of our understanding of the adaptive benefits and evolution of sociality.

Tuco-tucos (Rodentia:Ctenomyidae) are subterranean rodents endemic to South America, ranging from southern Peru to southern Argentina. There are over 50 described species within the genus Ctenomys. Of the species whose behavior has been described, the majority are thought to be solitary meaning that a single adult occupies its own underground burrow, which is spatially distinct from other such burrows. However, recent field surveys are revealing greater complexity of social structure than previously realized, warranting targeted research on the social behaviors of these species. For my dissertation, I aimed to describe the behavior of a population of a previously undescribed tuco-tuco from the highlands in northwestern Argentina (Ctenomys opimus), commonly referred to as the highland tuco-tuco. I targeted this species due to anecdotal reports that suggested this population of highland tuco-tucos may be social.

For my first chapter, I used visual observations and radiotelemetry to quantify the spatial movements and consequent social structure of adult highland tuco-tucos located at Laguna de los Pozuelos, Jujuy Province, Argentina (hereafter referred to as Pozuelos). This study revealed that this population consisted of both lone and group-living individuals, and that the number of individuals per group as well as the sex ratio within groups varied markedly. Further, I compared the spatial and social structure of individuals across ecological contexts (i.e., above- versus below-ground) as well as during the daytime and nighttime. I found that social relationships were robust regarding ecological context (above- versus below-ground), but that some groups identified during the daytime fissioned during the nighttime. Collectively, the findings from this chapter suggested that this population may be facultatively social.

For my second chapter, I aimed to confirm the possibility that the population of highland tuco-tucos located at Pozuelos are indeed facultatively social using spatial data collected over five consecutive years. From these data, I sought to (1) confirm the regular occurrence of both lone and group-living individuals within the population and (2) characterize the temporal consistency of individual social relationships. I found that while the study population consistently contained a mixture of both lone and group-living animals, individual spatial and social relationships varied markedly across time. Specifically, the extent to which individuals remained resident in the same location across years varied, as did the number of conspecifics with which an animal lived, with an overall tendency for individuals to live in larger groups over successive years. Collectively, this chapter indicated that population-level patterns of behavior in this population of C. opimus are consistent with facultative sociality but that this variation does not arise due to persistent differences in individual behavior.

For my third chapter, I sought to provide the first characterization of the glucocorticoid physiology in C. opimus and investigate how the observed variation in social behavior within the population of C. opimus at Pozuelos may impact individual glucocorticoid physiology. Earlier work in another known social tuco-tuco (Ctenomys sociabilis) found that yearling females that dispersed from their natal burrow to live alone had higher baseline glucocorticoid levels relative to females that remained in their natal burrow with conspecifics. Thus, for my third chapter, I aimed to determine if a similar pattern was also found in the population of highland tuco-tucos at Pozuelos. I collected fecal samples from all individuals captured on the field site during two consecutive years to assess the relationship between baseline glucocorticoid levels and multiple metrics of social behavior (i.e., group size, sex ratio of group, and metrics measured via social network analysis). Additionally, I conducted a biochemical validation study to confirm that fecal glucocorticoid metabolites provide robust measures of glucocorticoid levels in C. opimus. The results from the enzyme-linked immunosorbent assays revealed that corticosterone is the primary glucocorticoid metabolite produced by C. opimus. Despite marked variability in social relationships among the animals sampled, differences in social behavior did not appear to predict variation in fecal glucocorticoid metabolites. Rather, individual variability in fecal glucocorticoid metabolites was best explained by sex, with males having higher corticosterone levels than females. This pattern was also observed for individuals in the biochemical validation study. Collectively, this chapter underscores the importance of intrinsic factors (i.e., sex) in shaping glucocorticoid variation in wild populations of mammals.

For my fourth chapter, I sought to provide the first characterization of the gut microbiome in C. opimus and investigate how the observed variation in social behavior within the population of C. opimus at Pozuelos may impact diversity of gut microbiome composition both within and between individuals. Studies in other mammalian taxa have shown a strong link between gut microbiome diversity and sociality, such that individuals connected with more conspecifics had great microbial diversity. Additionally, these studies have shown that individuals within groups tend to have more similar gut microbiome compositions that individuals between groups, further demonstrating the effect of sociality on the gut microbiome. Thus, for my final chapter, I aimed to determine if a similar pattern was also found in the highland tuco-tucos at Pozuelos. I collected fecal samples from all individuals captured on the field site during two consecutive years to assess the relationship between gut microbiome diversity and multiple metrics of social behavior (i.e., group size, sex ratio of group, and metrics measured via social network analysis). I found that gut microbiome alpha diversity (diversity within an individual) was best predicted by eigenvector centrality and clustering coefficient, relative to other social network metrics. Further, I found that while gut microbiome beta diversity (similarity between individuals) was not correlated with social network metrics, it was correlated with degree of home range overlap between individuals, highlighting the importance of contact between conspecifics outside of an individual’s immediate social group. Additionally, I found that beta diversity clustered by year, likely due to differing preservation methods between field seasons. Sex did not explain variation in gut microbiome alpha or beta diversity. Collectively, this chapter provides the first description of the gut microbiome in highland tuco-tucos and suggests that horizontal transmission plays an important role in maintaining gut microbiome diversity in C. opimus.

Despite substantial evidence that global climates are changing, predicting organismal responses to such changes poses a vexing research challenge, in part because responses can vary dramatically, even among closely related species. Studies of chipmunks (Tamias spp.) in Yosemite National Park provide a unique opportunity to explore the reasons for variation in species-specific spatial and temporal responses to a century of environmental change. Comparisons of historic and modern distributions of these animals indicate that while the Alpine Chipmunk (T. alpinus) has experienced a marked upward elevational range contraction over the past century, the Lodgepole Chipmunk (T. speciosus) has undergone effectively no change in its elevational range during this period. The reasons for this striking difference in range response are poorly understood. I therefore chose to explore the roles of several biotic factors in shaping patterns of response by these species. Specifically, I focused on habitat specialization and dietary overlap as potential contributors to differences in range response.

I began by selecting three sites in Yosemite National Park where T. alpinus and T. speciosus co-occur, so that I could compare patterns of habitat use in areas of sympatry between the two species. I carried out live-trapping and radio-tracking of chipmunks at each site during the summers of 2011, 2012, and 2013. I integrated these data with analyses of vegetation cover (NDVI) to quantify interspecific differences in spatial overlap and habitat use. I found that considerable interspecific spatial overlap exists, creating high potential for interspecific competitive interactions to occur. I also report evidence for differences in habitat use, with T. alpinus typically found in areas with lower vegetation cover and T. speciosus in areas with relatively higher vegetation cover.

Building on the results of the NDVI analyses, I used field-collected microhabitat data to describe characteristics of habitats used by each species in greater detail and to assess degree of specialization in habitat use. I found evidence for interspecific differences in types of habitats used by each species, with lower tree cover and larger amounts of exposed rock in habitats occupied by T. alpinus. Interspecific differences also existed in habitat breadth, with higher variation in amount of downed wood in areas used by T. speciosus. These results are consistent with the characterization of T. alpinus as a high elevation specialist and suggest that the elevational range contraction reported for this species may reflect habitat tracking.

Finally, I took a longer-term approach by examining evidence for dietary changes and changes in cranial morphology in these species over the past century. Stable isotope analyses of hair samples from modern and historical museum specimens of each species collected at the same localities indicated that signatures of temporal dietary change were more pronounced in T. alpinus, although diet breadth did not appear to differ consistently between the study species. Morphometric analyses of crania from these specimens revealed significant temporal changes in cranial shape for T. alpinus, with less pronounced changes in shape for T. speciosus; evidence of selection on skull morphology was detected for T. alpinus but not T. speciosus. These results are consistent with growing evidence that T. alpinus is generally more responsive to environmental change than T. speciosus. However, the observation of large amounts of dietary change in T. alpinus is somewhat inconsistent with expectations based on habitat tracking— if T. alpinus has shifted range to remain in similar habitats over the past century, one would expect to see little change in diet. This in mind, our results emphasize the complex and often geographically variable nature of responses to environmental change.

In general, my findings suggest that habitat specialization may be associated with greater response to environmental change. My data underscore the complicated ways in which habitat use and dietary breadth act as contributors to range response. Future studies will build upon my findings to explore how local environmental conditions interact with interspecific differences in ecology and habitat use to generate variation in patterns of range change over time.

Mammalian mating systems are complex, encompassing both individual mate choice decisions and population-level patterns of spatial and social relationships among conspecifics. Major Histocompatibility Complex (MHC) genes are thought to be central to reproductive decisions in mammals due to the critical role of these loci in the adaptive immune response and the associated impacts on offspring success. It is generally accepted that individual MHC genotypes are communicated via the urine, making these genes ideal targets for studies of mammalian mate choice. At the individual level, animals are expected to prefer mates with MHC genotypes that are dissimilar from their own so as to increase MHC diversity and immunocompetence among their offspring. At the population level, the number of partners per individual is expected to increase pathogen exposure and lead to greater diversity at MHC loci. To date, however, tests of MHC-based mate choice patterns have been limited to analyses of only a few MHC loci in an otherwise large complex of genes. Such locus-specific studies have generated contradictory outcomes both within and across taxa, likely due to variation in the specific functions of individual genes, which may result in differences in the selective pressures experienced by different MHC loci. Moreover, despite the logical link between increased social contact, pathogen exposure, and immunogenetic diversity, correlations between mating system and adaptive immunogenetic diversity have seldom been studied. To generate a more comprehensive understanding of the relationships between reproductive behavior and immunogenetic variation, this dissertation project used genomic and transcriptomic technologies to examine variation at numerous MHC and non-MHC immunogenes in wild Peromyscine rodents characterized by very different mating systems.

Using a combination of field and molecular techniques, the first chapter tests for patterns of disassortative mating at adaptive MHC Class I and II genes in two populations of free-living California mice (Peromyscus californicus), an obligately monogamous species. Additionally, this chapter compares patterns of genetic diversity between adaptive and innate immunogenes as well as non-immunogenes in two populations of California mice. Analyses of molecular variation between male-female pairs revealed that reproductive partners were not more dissimilar than expected under random mating at adaptive, innate, or non-immunogenes, providing no evidence to support MHC-based disassortative mating in this species. Analyses also revealed high levels of genetic differentiation between populations at both adaptive and innate immunogenes, suggesting that immunogenetic variation in California mice reflects local differences in pathogen exposure rather than disassortative mating based on variability at MHC Class I and II genes.

While the first chapter explores correlations between individual-level mate choice decisions and immunogenetic diversity, the second and third chapters focus on understanding the role of mating system in shaping patterns of immunogenetic diversity. Towards this aim, the second chapter used an RNAseq approach to study the gene expression profiles of liver tissue – a highly immunoactive organ – from sympatric populations of the monogamous P. californicus and two highly promiscuous congeners (P. maniculatus and P. boylii). These analyses revealed distinct patterns of gene expression between species, with most of this variation explained by mating system. These differences were particularly pronounced for MHC genes. In particular, MHC Class I genes were found to be over-expressed in the two polygynandrous species, as expected if exposure to sexually transmitted pathogens varies with mating system.

The third chapter used RNAseq-generated genotype data to examine genetic variation between monogamous and polygynandrous species across multiple populations, thereby examining how relationships between mating systems and immunogenetic variation differ across a habitat gradient. Across populations, immunogenetic diversity was consistently higher in the two polygynandrous species at MHC Class I and II genes, as well as at the multidrug resistance protein gene (mdr1) – an important immune related gene - suggesting that mating system affects diversity at a variety of immune related genes. Overall, these data indicate that immunogenetic variation in Peromyscines is correlated with reproductive behavior, rather than geographic locality or habitat type, and suggest that balancing selection may be important in maintaining variation at MHC genes in California mice, albeit at relatively lower levels.

Collectively, these analyses generate new insights into relationships among mate choice, mating systems, and immunogenetic variation in free-living, non-human mammals. This work demonstrates the important interplay between mate choice and mating system, indicating that mating system has profound effects on immunogenetic diversity that may ultimately impact the importance of immunogenetic traits during mate choice. Further, it highlights the numerous mechanisms through which variation at MHC genes may be maintained in wild populations and underscores the role of behavior in maintaining this adaptive variation.

For many species, a critical component of an animal's environment is its social setting, specifically whether an animal lives alone or with conspecifics. Living in a group may confer benefits associated with cooperation but almost invariably comes with costs resulting from conflict and competition. In contrast, living alone may reduce costly interactions with conspecifics but likely requires greater effort when caring for young, finding food, or avoiding predators. My research investigates the adaptive (fitness) and physiological consequences of group living using the social system of the colonial tuco-tuco (Ctenomys sociabilis), a subterranean rodent endemic to southwestern Argentina. Unlike most species in the genus Ctenomys, colonial tuco-tucos are social with burrow systems shared by 2 - 6 females and, sometimes, one male. However, not all females live in groups. About one-third of the burrow systems in the population are comprised of females that have dispersed to live alone, providing a rare opportunity to explore the effects of naturally occurring social variation on the fitness and physiology of individuals living in groups and alone.

Previous studies of C. sociabilis have shown that living alone is associated with significant differences in survival and direct fitness compared to remaining in the natal group. Because social setting may also substantially impact proximate factors such as individual physiology, I examined the effects of intraspecific differences in social setting on measures of baseline glucocorticoid (GC) levels. GCs are adrenal steroids critical to maintaining homeostasis. As such, GCs provide an appropriate gauge of the physiological response to social and physical stressors. By combining data on GC variation in free-living animals with experimental manipulation of housing conditions for captive individuals, I tested the hypothesis that living and breeding alone are associated with increased GC levels in this species. I also investigated how group size and composition correlate with GCs in group-living individuals. These resulting data indicate the social environment is an important determinant of baseline GC levels and that these effects vary with group composition. Collectively, these analyses yield important new insights into physiological consequences of sociality.

In colonial tuco-tucos, variation in the social environment also includes whether or not an adult male is present in the communal nest of this plural-breeding rodent. Due to high mortality, males are not found in all burrow systems. When a male is present in a colony, the time spent in the nest with pre-weaned offspring does not differ than that of females. Male assistance with young is rare for mammals, and for this part of the study, I tested two major hypotheses explaining male next attendance - the parental effort hypothesis and the mating effort hypothesis. Combining evidence from the field and lab, I found that male nest attendance did not increase the number or growth of young, nor future access to the females in the burrow system. However, the presence of an adult male increased the survival of male - but not female - pups. This result, along with observations in the lab indicating that adult males affected the pubescent onset of aggressive interactions between male pups, suggests that they may play a critical role in the development of male offspring, thereby affecting survival.

Social affiliation and group living are seminal aspects of some of the most exciting and intensely studied topics in behavioral biology, from the field of human psychopathology to investigations of cooperation and reproductive skew in animal societies. Understanding how and why sociality evolves as an alternative to the much more common trait of solitary living has long been a topic of special interest among biologists, particularly in light of evidence that group living can impose a number of costs (e.g., increased exposure to pathogens or increased resource competition) that can negatively impact direct fitness. It is hypothesized that sociality only evolves when the benefits associated with cooperation outweigh the costs of competition. Social animals are therefore likely exposed to a unique set of evolutionary pressures as a result of the distinct costs and benefits inherent to their gregarious lifestyles, and social animals should consequently exhibit adaptations that specifically counterbalance the costs associated with sociality. For my dissertation, I set out to explore the evolutionary consequences of sociality by investigating patterns of genomic variation and change in social and solitary animals from a population-level and a broad, comparative perspective, respectively.

The first two chapters of my dissertation serve as a comparative case study on the impacts of sociality on population structure in a novel rodent system. I present population-level genomic data from two species of pebble-mound mice (genus Pseudomys, family Muridae) endemic to mainland Australia: the solitary Queensland pebble-mound mouse (P. patrius) and the social Ngadji (P. chapmani). Like other pebble-mound mice, these focal species construct large aggregations of pebbles over their subterranean burrows that, although not necessary for survival, are required by females for mating. As a result of their distinct social systems, these closely related and ecologically similar congeners serve as compelling point of comparison. By characterizing patterns of genomic variation within each of these species, I demonstrate differences in population structure between the two species, particularly in relationship to pebble-mounds and kinship. In Chapter 1, I demonstrate that the Queensland pebble-mound mouse exhibits significant evidence of kin structure despite being solitary. In this particular case, kin structure seems to arise as a result of the spatially fixed resources (i.e., pebble-mounds) sought out by females. Because affiliations among close kin are very typical of social animals, these findings raise questions about how social and solitary animals might aggregate differently. These questions are then addressed in Chapter 2, where I demonstrate that the social Ngadji also exhibits kin stratification around pebble-mounds, but on a much broader scale than in the Queensland pebble-mound mouse. Beyond describing the molecular ecology of these two non-model species, this work demonstrates that population-level studies that utilize comparative frameworks of closely related and ecologically similar species can provide insights into the impacts of sociality on dispersal and mating system that might inform future studies on the ecological conditions and behavioral mechanisms underlying group living.

Whereas the first two chapters consider the impacts of social system on general, population-level processes, the final chapter tests an explicit hypothesis about the evolutionary consequences of sociality on a broader comparative scale. Of all the proposed costs associated with group living, increased exposure to pathogens may be one of the most important: not only are pathogen exposure and disease susceptibility are two of the greatest influences on an individual’s reproductive success, but communicable diseases are known to thrive in communities characterized by group living and high rates of conspecific interaction. However, attempts to explicitly demonstrate the putative immunological consequences of sociality have historically proven difficult. For example, consider two ecologically similar species that share recent common ancestry but demonstrate distinct social organizations. One might attempt to characterize differences in immune pressures by measuring differences in pathogen exposure or parasite loads between the two species. However, divergence among species generally leads to divergence among their respective pathogens and parasites, such that measures of pathogen or parasite loads may become entirely incomparable between the two species. Similarly, this approach assumes that no adaptations (physiological, behavioral, or otherwise) have arisen since the divergence of the two species that might counteract their respective immune pressures. Rather than attempting to quantify the extent of immune-related evolutionary pressures by assessing pathogen or parasite prevalence, Chapter 3 characterizes the relative pathogen-mediated pressure acting on social and solitary species by assessing positive selection in immune orthologues from nine species across three divergent mammal lineages. These analyses demonstrate that relatively social and solitary mammals experience distinct evolutionary pressures, with group-living species experiencing faster rates of evolution at immune loci. When considered in conjunction with candidate loci studies in more limited taxonomic comparisons, these findings suggest that increased immune burden is one of the more common costs associated with sociality.

Biotic responses to environmental change can vary markedly, even among closely related, ecologically similar species. Such responses may be conspicuous (e.g., climate-associated range shifts) or they may be subtler and more challenging to detect. In the latter case, organisms may use individually variable mechanisms, including modifications of behavior and physiology, to cope with environmental change in situ. Further, in addition to providing mechanisms of response to environmental change, behavioral and physiological traits may be indicators of habitat suitability. Thus, to understand and, ideally, to predict how species will respond to environmental change, it is necessary to determine which traits are associated with vulnerability and to identify which factors constrain range limits for vulnerable species. My dissertation focuses on the behavior and physiology of the alpine chipmunk (Tamias alpinus) and the lodgepole chipmunk (T. speciosus), two co-occurring, closely related species that have been characterized by very distinct spatial responses to environmental change in Yosemite National Park, CA. Over the past century, T. alpinus has contracted its range upward in elevation; during the same period, T. speciosus has displayed no significant elevational range shift. To assess the role of behavioral and physiological variability in generating these responses, I explored interspecific differences in baseline stress hormone (glucocorticoid, GC) levels and behavioral activity budgets with the goal of identifying the environmental factors that are most important for determining range limits in the study species. First, I validated a non-invasive method to measure fecal GC metabolites (FGMs) in both study species. By exposing captive individuals to a series of controlled challenges, I also identified interspecific differences in stress reactivity, with T. alpinus being generally more stress-responsive. Next, I validated the use of accelerometers to remotely document the behavioral activity budgets of the study species, demonstrating that these sensors can be employed to collect behavioral data from free-living animals. I then deployed accelerometers across broader spatial and temporal scales. I used the resulting data to construct models that integrate intrinsic biological and environmental parameters to identify key predictors of activity in each species. I found that, compared to T. alpinus, activity in T. speciosus was characterized by generally greater inter-individual variance and greater variability in response to environmental parameters. Finally, I used FGM data collected over three years and at multiple sites in and around Yosemite National Park in conjunction with data regarding multiple extrinsic (environmental) and intrinsic (life history) parameters to identify the factors that best predict FGMs in the study species. These analyses revealed FGM levels are more strongly related to environmental parameters in T. alpinus than in T. speciosus. In summary, my research indicates that T. alpinus is more stress-responsive to external, environmental challenges, and potentially less flexible in responding behaviorally to environmental conditions than T. speciosus. Overall, these results indicate that behavior and physiology are likely to be important determinants of a species’ response to environmental change. These findings also suggest that individual species vary in their general sensitivity to environmental change, with some species being more change-responsive than others.

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.