PAST CLIMATE SET THE STAGE FOR FUTURE RESPONSES TO CLIMATE CHANGE

Within a species, variation is an important factor determining its potential to evolve in the face of future climate change. The paleontological record can provide snapshots in time to demonstrate how morphological variation covaries with environmental variables in ecologically relevant traits. By extensively sampling vole fossil localities I trace morphological variation in Microtus californicus molars through time and across California over the last 45,000 years. I compare the effects of climate change on this species at the population and species levels. I find that molar shape is significantly correlated with mean annual temperature in this species. As California has become increasingly warm, M. californicus has lost approximately 30 percent of the molar variation that is correlated with high temperatures. In fact, in recent years we are already seeing likely extirpations in populations that once lived in some of the hottest portions of this species range. Future climate change is likely to stress the species to the extent that additional populations in increasingly extreme habitats may be extirpated. More importantly, this study demonstrates the rapidity with which climate change can stress even extremely rapidly reproducing small mammals such as voles.