Palaeodemographics of small-bodied mammals in Pleistocene environments: a case study of muskrats (Ondatra zibethicus: Rodentia: Muridae) from north Florida

Abstract

The effects of environmental change on fecundity and mortality rates of ancient populations are likely to have influenced extinction patterns and biogeographical range shifts. To test for a relationship between environmental change and palaeodemographical change, the mortality profiles of late Pleistocene muskrats (Ondatra zibethicus) from north Florida were compared with recent populations of the same species to assess the effect of the Pleistocene–Holocene transition on the demographics of this species, as well as a potential role in the extirpation of O. zibethicus in Florida during the Pleistocene–Holocene transition. At the older locality (Latvis-Simpson: approximately 32 14C Ky BP), there is strong sedimentological evidence for late summer or autumn seasonal deposition. Most of the individuals in the youngest cohort were adults approximately 7 or 8 months old at death, suggesting that the breeding season had occurred in the fall or winter. This breeding schedule is similar to recent southern populations where breeding is most intense in the fall and winter, and unlike northern populations where breeding occurs in the spring. The inferred breeding seasonality is consistent with other evidence suggesting that the south-east was warm and equable in the late Pleistocene. At the younger locality (Sloth Hole: approximately 12 14C Ky BP) muskrats exhibit faster dental wear and lower life expectancy, suggesting harsher conditions near the time of extirpation. Cooler temperatures, aridity, water table fluctuation, and human presence all comprise potential factors leading to a lower life expectancy during this time interval. The fossil record shows a potential for investigating links between climate change and the demographics of palaeopopulations. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 41–56.