Stasis and change in Holocene small mammal diversity during a period of aridification in southeastern Utah

Abstract

Biological conservation depends on understanding and disentangling the effects of decadal- to centennial-scale dynamics from the millennial-scale dynamics documented in the fossil record. The American Southwest is expected to become increasingly arid over the next few decades and will continue to experience large-scale human land use in various forms. A primary question is whether the ecological fluctuations recorded over the past few decades fall outside the range of variation expected in the absence of recent land use and management. I excavated and quantified mammal diversity change in two fossil-bearing alcoves, East Canyon Rims 2 and Rone Bailey Alcove, located in San Juan County, Utah. AMS radiocarbon dates on 33 bone samples from these sites span ~4.4–0.5 kyr and shed light on pre-industrial faunal dynamics in the region over the course of environmental change. Localities with comparable small mammal diversity have not been reported from this region previously, so these deposits provide novel insight into Holocene mammal diversity in southeastern Utah. Taxa recorded in these sites include leporids, sciurids, perognathines, arvicolines, Onychomys, Cynomys, Dipodomys, Peromyscus, Neotoma, and Thomomys. Using temporal cross-correlation, I tested for a relationship between regional temperature and species richness, evenness, relative abundance, and rank abundance. I also tested for changes in the overall taxon abundance distribution and visualized faunal relationships among time bins using non-metric multidimensional scaling of relative abundance data. None of the measures of diversity tested here were correlated with temperature change through time except for relative abundance of leporids. Overall, these results suggest that climatic fluctuations of the magnitude preserved in these deposits did not significantly alter the small mammal community, nor is there evidence that the presence, then exodus, of Native Americans from the region significantly affected small mammals.