USING THE PALEONTOLOGICAL RECORD OF MICROTUS TO TEST SPECIES DISTRIBUTION MODELS AND REVEAL RESPONSES TO CLIMATE CHANGE

This study reconstructs the Quaternary distributions of five Microtus species from the Pacific Coast of the United States using 144 newly identified Microtus fossils, including the first fossil Microtus oregoni and Microtus townsendii. We use these reconstructions to explore three hypotheses: (1) congeners respond to different aspects of changing climate; (2) recent patterns and rates of range change over the last 100 yrs of intense climate change are similar to those experienced by the same species since the Last Glacial Maximum (~21kya; LGM); and (3) species distribution models (SDMs) projected into the past are concordant with the empirical data on Microtus species distributions. We find that individual Microtus species shifted their ranges incongruently since the LGM in response to different climate variables. In at least two of these species, M. montanus and M. longicaudus, recent climate responses (over the last 100 yrs) are concordant with those of warming at the LGM, but rates of elevational ascension increased in M. longicaudus over the last 100 years. Inconsistencies between LGM SDMs and Quaternary fossil ranges indicate potential problems with LGM precipitation reconstructions, although interspecific interactions can not be ruled out as the cause of these differences. Overall, the study highlights the need for more, detailed species-level palaeodistributions to put recent observations in a broader temporal context and examine the effectiveness of SDMs and LGM climate reconstructions.