How have climate indices of small mammal communities in the Sierra Nevada changed over the past 100 years?

Background/Question/Methods

Novel communities are formed as species shift their ranges in response to recent climate change. This phenomenon often occurs in montane ecosystems, whereby high topographical complexity creates compressed climate regimens across elevation. We know much about species-specific elevational range shifts, but how communities of species and their properties shift in response to climate change remains relatively unexplored. To understand how properties of montane communities change, we compared historical data collected 100 years ago and current data on small-mammal communities. These data were collected along two elevational transects in Yosemite (YO) and Sequoia/Kings Canyon (SS) National Parks in California's Sierra Nevada. We quantified the community-precipitation index (CPI) and the community-temperature index (CTI) for historical and modern sites, measured as the median precipitation and temperature preferences for each species present. We expected CPI to decrease and CTI to increase because of a decline in precipitation and a rise in temperature over the past century.

Results/Conclusions

As expected, CPI across elevations decreased between historical and modern eras, suggesting that communities have shifted to more drought-adapted species. However, we found no increase in CTI between historical and modern sites except for low elevation sites in YO. These results show that modern small-mammal communities are composed of more drought-adapted species but not necessarily more warm-adapted species. This study highlights the importance of incorporating multiple aspects of climate when monitoring species' responses to climate change.