MORPHOLOGICAL AND DIETARY RESPONSES IN THE GRANIVOROUS HISPID POCKET MOUSE (CHAETODIPUS HISPIDUS) TO CLIMATE CHANGE AND BIODIVERSITY LOSS OVER THE LATE QUATERNARY

The late Quaternary saw dramatic landscape changes across North America. The loss of most megafauna (mammoths, saber-tooth cats, etc.) at the end of the Pleistocene and an overall warming climate throughout the Holocene had wide-spread effects across mammalian communities. Using the fossil record, studies on small mammal species have shown that individual taxa can respond in broadly different ways to the both the biotic and abiotic changes that occurred across this time span. Here we characterize morphological and dietary changes in the hispid pocket mouse (Chaetodipus hispidus) from a single fossil locality (Hall’s Cave, Texas) across the past 16,000 years. Employing 12 time intervals, we used fossil mandible toothrow measurements (N=338) and bone collagen (N=159) carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values to examine changes in body size and diet through time. We find a significant decrease in the body size of Chaetodipus hispidus through time. Decreased mass was more strongly correlated with increasing environmental temperature and decreasing precipitation than to changes in community composition (richness and turnover). Thus, body size in C. hispidus responded primarily to climate change over this period, with impacts from changes in community structure being secondary. We find a significant decrease in δ¹⁵N values over time, but no significant changes were seen in δ¹³C values, suggesting that C. hispidus foraged across similar primary resources, and potentially decreased in insectivorous activity through time. However, decreasing δ¹⁵N values are consistent with past studies of different rodent species at Hall’s Cave during this period and may therefore be the result of a baseline shift – decreased δ¹⁵N values of the plants in the region. Overall, our results suggest a primarily morphological response in Chaetodipus hispidus, mainly driven by variation in climate, with changes to species interactions through community restructuring affecting the response of the taxa to a lesser degree.