Print PageThe impacts of climate change on species are complex, manifested in changes not just in temperature and precipitation but also on habitat, food availability, and interspecific interactions. Unfortunately, baseline historical population data are rare. As part of the Grinnell Resurvey Project, I capitalized on detailed field surveys conducted across the mountains of California by the U.C. Berkeley Museum of Vertebrate Zoology in the early 1900’s to understand the changes in meadows and mammals over the last century. I focused on the Belding’s ground squirrel (Urocitellus beldingi), a mid- to high- elevation meadow specialist. Specifically, in 2010 and 2011, I resurveyed 75 sites from the southern Cascade Range to Sequoia National Park with documented historical U. beldingi occurrences. I conducted visual and trapping surveys of the meadows in a 2 kilometer radius around these sites, recording sightings of U. beldingi as well as information about vegetation, proximity to water, and meadow size, and presence of other ground squirrel species. I then modeled the probability of site extinction considering these factors as well as habitat change, grazing, and BIOCLIM temperature and precipitation variables.
Results/Conclusions
The per visit probability of detection (p) for U. beldingi was 95% and most sites were visited more than once. Their site extinction rate was very high (45%), with no recorded colonizations. The disappearance of U. beldingi across the landscape correlated with climate as well as habitat degradation: U. beldingi were more likely to disappear from hotter and lower sites, with currently occupied sites 450m higher on average than historically occupied sites. There was also a correlation with the presence of other species: U. beldingi disappeared more often from sites where California ground squirrels, Otospermophilus beecheyi, occurred. Given that O. beecheyi are habitat generalists that occur primarily at low- to mid-elevations, I explore whether this pattern is a result of increased habitat disturbance or signifies an upslope range shift for both species as climate warms. I also look at the changes in meadows over the last century and how that correlates with the loss of U. beldingi. Exceptions to the phenomenon of disappearing U. beldingi at mid-elevations were found in irrigated lawns, parks, and agricultural fields. Thus, the results of this study point to anthropogenic refugia as potential opportunities for maintaining meadow specialists in in the face of climate change.
