Genetics, Ecology, and Conservation of Montane Populations of Colorado Chipmunks (Tamias quadrivittatus)

Abstract

Population genetics and ecological characteristics were assessed in relictual montane populations of the Colorado chipmunk ( Tamias quadrivittatus ). This study focused on conservation and systematic relationships of two endangered populations of T. quadrivittatus inhabiting the Oscura and Organ mountains of central and southern New Mexico, relative to coniferous-forest populations found in northern latitudes. Results suggest that inbreeding has had a significant effect on genetic structure of populations of chipmunks, particularly in more arid regions of central and southern New Mexico. Levels of intrapopulation variability were a function of population size, as indicated by the significant association between area of forest habitat and average values of allelism, polymorphism, and heterozygosity. Patterns of allozymic differentiation in the northernmost populations can be explained by dispersal, in which populations connected by corridors of mesic woodland during the Pleistocene or Recent received sufficient gene flow to account for the generally low level of interpopulation genetic divergence. Conversely, genetic divergence in central and more arid southern populations likely is a result of isolation and subsequent genetic drift associated with fragmentation of formerly continuous forest vegetation since the Pleistocene. Most relict-montane populations of T. quadrivittatus in New Mexico are small and patchy in distribution because of a close affinity with specific ecological parameters. These genetically depauperate populations are particularly susceptible to extinction owing to increasing human-induced destruction of habitat, as well as vagaries of stochastic demographic and environmental phenomena. A goal of resource management in the southwestern United States must be to preserve relict-mountaintop ecosystems that represent unique biogeographic links to the evolutionary history of the region. Within these mesic woodland and forest patches, special effort must be made to preserve as much of the species pool as possible, owing to increased habitat destruction and fragmentation. Based on results of genetic, morphologic, and ecologic data, a new subspecies of the Colorado chipmunk from the Oscura Mountains, New Mexico, is described.