THE EFFECTS OF CLIMATE CHANGE AND MEGAFAUNAL EXTINCTION ON BODY SIZE AND DIET IN THE HISPID POCKET MOUSE (CHAETODIPUS HISPIDUS) OVER THE LATE QUATERNARY

The unprecedented, size-selective, end-Pleistocene extinction resulted in a significant loss of North American mammalian fauna—including all species larger than 600 kg. Considerable research has focused on the large-bodied victims of this extinction, but to date, little is known about the impact on the surviving small mammal species. This biodiversity loss was coupled with drastic change in climate. Many mammal species demonstrate a negative correlation between population body size and environmental temperature; an ecogeographic pattern known as Bergmann’s rule. In addition, rapid changes in landscape and community dynamics may impact resource availability for small mammals.

Here, we characterize the influence of climate and biodiversity loss throughout the late Quaternary on the hispid pocket mouse (Chaetodipus hispidus) from Hall’s Cave, Texas. Using a well dated fossil record, we analyzed the changes in the population body size and diet of C. hispidus across the last 16,000 years. In total, more than 500 specimens were examined, equaling approximately 45 specimens (30 for body size and 15 for diet) from each of 12 time intervals (~1.3 ka duration). Body size was estimated from the lower tooth row length and diet was determined from carbon (δ¹³C) and nitrogen (δ¹⁴N) isotopes of bone collagen from fossil mandibles. We found that population body mass varied from 11 to 32 g across time. Preliminary results show a significant decrease in the variability and average body size across the Quaternary. In contrast, dietary niche, measured as the ratio of C/N isotopes, appears to remain relatively unchanged. These results are concordant with decreases in body size in relation to climate warming as well as dietary changes across other small mammal species. Our findings suggest population body size of small mammals may be impacted by broad climate warming, vegetation shifts, and biodiversity loss, while diet is influenced by changes on a more localized scale.