Current Research

After a successful decade spent conducting resurveys of birds and small mammals in the Sierra Nevada Mountains and Coast Range of California, resurveys are underway in two of the remaining ecoregions that we have yet to revisit: Deserts and the Central Valley. Follow-up studies are also underway that test mechanisms that could account for specific results found in the Sierra Nevada range shifts from our earlier work. The goals of these three areas of inquiry are complementary.

Resurveys to Understand Vertebrate Community Changes in Warm and Cold Deserts

We are resurveying terrestrial endotherms (birds and mammals) at sites in California deserts and adjacent sky islands that were originally surveyed prior to 20th century climate change by Joseph Grinnell and colleagues at the Museum of Vertebrate Zoology (MVZ) at UC Berkeley (UCB) from 1904 to 1945. These include sites in and adjacent to Death Valley National Park (NP), Mojave National Preserve, and Joshua Tree NP, as well as elevational transects in the sky islands of the San Jacinto and White/Inyo Mts. From their extensive sampling, Grinnell et al. left detailed field notes including standardized bird counts and small mammal trapping, habitat observations, specimens, maps and images. A century later, scientists from the MVZ, San Diego Natural History Museum, UC Santa Cruz, the University of New Mexico, and the National Park Service are collaboratively retracing Grinnell’s path to assess how terrestrial vertebrates have responded to environmental change and to establish another benchmark for future comparison.

Funded by grants we received in 2015 from the National Science Foundation and the National Geographic Society (P.I. Steve Beissinger), this research will advance theory and understanding of faunal responses in a climate-change hotspot (California deserts) characterized by climatic extremes by using a unique historical resource (Grinnell-era surveys) to examine both local colonization and extinction (turnover) over the past century.

We will address three related questions in a harsh (arid and hot) environment that has already experienced strong warming and drying, and is forecast to become hotter and drier:

1. To what degree are differences in site-level turnover among species driven by physiological limitations, climatic variation, habitat change, species interactions, and species traits?
2. Has recent warming resulted in individualistic or community shifts in species composition?
3. Have phenotypes and niches responded to climate change, and do responses differ between species with shifting or static ranges?

To answer these questions we: (a) resurvey birds and small mammals in the Sonoran, Mojave and Great Basin deserts with varying degrees of climate change; (b) model turnover at sites in relation to multiple factors; (c) develop and test ecophysiological models of endotherms that relate climate to habitat suitability and population dynamics; and (d) measure change in phenotypic and isotopic niche space.

You can read more about this research here.

Resurveys to Disentangle the Effects of Climate and Land Use Change

The combined effects of climate and land-use change on species distributions are largely unexamined. Managers rely on existing theory translated through model projections to anticipate how climate, land use, and species-specific sensitivity will interact to alter species distributions. There is a pressing need to validate theory and models by comparing 20th century changes in species occurrences to forecasts. The few studies that have used historical data, including our own past resurveys, have focused on protected areas in order to isolate the effects of climate. Moreover, there are likely synergies between climate and land-use change that have not yet been quantified and are not accounted for in most projections of the impacts of global change. If land-use changes are not properly considered, they will introduce variation that can reverse, hide, or exacerbate our perception of climate change impacts.

The final frontier for the Grinnell Resurvey Project is to quantify species turnover (site-level extinction and colonization) at historically surveyed sites in the Central Valley and its urban fringes extending into California’s largest metropolitan areas in Los Angeles, San Francisco and Sacramento. Resurveys of bird occurrences will be combined with resurveys already completed in the Coastal Range and Sierra Nevada, and ongoing surveys in the Mojave Desert to analyze species turnover at a scale that covers the state of California.

This project will require some serious work to reconstruct land use during the time Grinnell et al.surveyed these sites and then producing valid measures of land use change to compare, along with climate change measures, to avian turnover.

This research is being led by Sarah MacLean, a Ph.D. student who is working with Steve Beissinger. You can read more about this research here.

Follow-up Studies from the Sierra Nevada Resurvey to Determine Mechanisms Underlying Range Shifts

Our resurveys of the small mammals in the Sierra Nevada mountains found large heterogeneity in elevational shifts among species – even among congeneric species - in the response to a century of climate change. Several patterns of variation in the elevational range shifts small mammals warranted further investigations to determine the mechanisms involved. Two graduate students are completing Ph.D.s in Professor Eileen Lacy’s lab studying variation in closely related species of chipmunks.

Comparisons of historic and modern distributions indicate that the alpine chipmunk (T. alpinus) has experienced a marked upward elevational range contraction over the past century, while the lodgepole chipmunk (T. speciosus) has undergone little change in its elevational range during the same period in Yosemite National Park.

Rachel Walsh’s work explores the roles of habitat specialization and dietary overlap as potential contributors to differences in range response, comparing patterns of habitat use in areas of sympatry between the two species, integrating live-trapping and radio-tracking of chipmunks and with analyses of vegetation cover (NDVI) and microhabitat. She found considerable interspecific spatial overlap exists, creating a high potential for competitive interactions to occur. However, T. alpinus was typically found in areas with lower vegetation cover and T. speciosus in areas with relatively higher vegetation cover. 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 (conducted with collaborator Ana Paula Assis) from these specimens revealed significant temporal changes in cranial shape for T. alpinus, with less pronounced changes in shape for T. speciosus. These results are consistent with growing evidence that T. alpinus is generally more responsive to environmental change than T. speciosus. Read more details at http://ib.berkeley.edu/labs/lacey/walsh2.html.

Tali Hammond’s dissertation uses stress physiology and behavioral activity budgets as tools to understand the roles that different environmental factors (climate, species co-occurrence, vegetation, human disturbance) play in determining where T. alpinus and T. speciosus live. Few empirical studies on terrestrial, wild mammals examine a direct link between physiology and distributional shifts in response to climate change, and behavioral studies are only now beginning to be explored in these systems. Elucidating these sorts of mechanisms will allow for improved forecasting of mammalian response to projected climate change. Thus far, her work suggests that T. alpinus is more sensitive to certain stressors than T. speciosus. Future results will shed light on how various environmental factors differentially cause stress to each species. Read more details at http://ib.berkeley.edu/labs/lacey/hammond2.html.