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Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2015)

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.

    Cover page: The Roles of Ecology and Habitat Use in Explaining Range Shifts by Chipmunks in Yosemite National Park
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2016)
    Predicting how individual taxa will respond to climatic change is challenging, in part because the impacts of environmental conditions can vary markedly, even among closely related species. Studies of chipmunks (Tamias spp.) in Yosemite National Park provide an important opportunity to explore the reasons for this variation in response. While the alpine chipmunk (T. alpinus) has undergone a significant elevational range contraction over the past century, the congeneric and partially sympatric lodgepole chipmunk (T. speciosus) has not experienced an elevational range shift during this period. As a first step toward identifying the factors underlying this difference in response, we examined evidence for dietary changes and changes in cranial morphology in these species over the past century. Stable isotope analyses of fur samples from modern and historical museum specimens of these species collected at the same localities indicated that signatures of dietary change were more pronounced in T. alpinus, although diet breadth did not differ consistently between the study species. Morphometric analyses of crania from these specimens revealed significant 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 for T. speciosus. These results are consistent with growing evidence that T. alpinus is generally more responsive to environmental change than T. speciosus, but emphasize the complex and often geographically variable nature of such responses. Accordingly, future studies that make use of the taxonomically and spatially integrative approach employed here may prove particularly informative regarding relationships between environmental conditions, range changes, and patterns of phenotypic variation.
      Cover page: Morphological and dietary responses of chipmunks to a century of climate change
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2014)
      Understanding recent biogeographic responses to climate change is fundamental for improving our predictions of likely future responses and guiding conservation planning at both local and global scales. Studies of observed biogeographic responses to 20th century climate change have principally examined effects related to ubiquitous increases in temperature - collectively termed a warming fingerprint. Although the importance of changes in other aspects of climate - particularly precipitation and water availability - is widely acknowledged from a theoretical standpoint and supported by paleontological evidence, we lack a practical understanding of how these changes interact with temperature to drive biogeographic responses. Further complicating matters, differences in life history and ecological attributes may lead species to respond differently to the same changes in climate. Here, we examine whether recent biogeographic patterns across California are consistent with a warming fingerprint. We describe how various components of climate have changed regionally in California during the 20th century and review empirical evidence of biogeographic responses to these changes, particularly elevational range shifts. Many responses to climate change do not appear to be consistent with a warming fingerprint, with downslope shifts in elevation being as common as upslope shifts across a number of taxa and many demographic and community responses being inconsistent with upslope shifts. We identify a number of potential direct and indirect mechanisms for these responses, including the influence of aspects of climate change other than temperature (e.g., the shifting seasonal balance of energy and water availability), differences in each taxon's sensitivity to climate change, trophic interactions, and land-use change. Finally, we highlight the need to move beyond a warming fingerprint in studies of biogeographic responses by considering a more multifaceted view of climate, emphasizing local-scale effects, and including a priori knowledge of relevant natural history for the taxa and regions under study.
        Cover page: Beyond a warming fingerprint: individualistic biogeographic responses to heterogeneous climate change in California
        • Article
        • Peer Reviewed
        Berkeley Research Impact Initiative (BRII) (2017)
        Preparing students to explore, understand, and resolve societal challenges such as global climate change is an important task for evolutionary and ecological biologists that will require novel and innovative pedagogical approaches. Recent calls to reform undergraduate science education emphasize the importance of engaging students in inquiry-driven, active, and authentic learning experiences. We believe that the vast digital resources (i.e., “big data”) associated with natural history collections provide invaluable but underutilized opportunities to create such experiences for undergraduates in biology. Here, we describe an online, open-access educational module that we have developed that harnesses the power of collections-based information to introduce students to multiple conceptual and analytical elements of climate change, evolutionary, and ecological biology research. The module builds upon natural history specimens and data collected over the span of nearly a century in Yosemite National Park, California, to guide students through a series of exercises aimed at testing hypotheses regarding observed differences in response to climate change by two closely related and partially co-occurring species of chipmunks. The content of the module can readily be modified to meet the pedagogical goals and instructional levels of different courses while the analytical strategies outlined can be adapted to address a wide array of questions in evolutionary and ecological biology. In sum, we believe that specimen-based natural history data represent a powerful platform for reforming undergraduate instruction in biology. Because these efforts will result in citizens who are better prepared to understand complex biological relationships, the benefits of this approach to undergraduate education will have widespread benefits to society.
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