Temporal Fluctuations in Density and Diversity of Desert Rodent Populations

Abstract

Species composition and density were studied in two areas on a watershed in the Chihuahuan Desert in southern New Mexico. The upper portion of the watershed, a creosotebush community, supported “resident” populations of Dipodomys merriami, Perognathus penicillatus, Neotoma sp., and Onychomys torridus. The lower portion of the watershed, which drained into a grass-covered dry lake, supported Sigmodon hispidus, Reithrodontomys megalotis, Dipodomys ordii, and Spermophilus spilosoma, in addition to the species found in the creosotebush area. Most “resident” species responded to fluctuations in rainfall and primary production by reduction in density during drought periods and a 10 to 12 month lag in population recovery during extended periods of favorable rainfall and plant production. Transient species such as Peromyscus sp. and Mus musculus established breeding populations on both sites during periods of more mesic conditions and reached densities that exceeded those of “resident” species. The rapid increase in population numbers of transient species when compared to the resident heteromyids was due to the higher reproductive potential of the cricetids. The species diversity index (H') nearly doubled during a period of above average rainfall which was proceeded by drought. Changes in species diversity in time was correlated with rainfall and productivity. The dynamics of these Chihuahuan Desert rodent communities are considered in terms of immigration and extinction as the suitability of habitat islands change through time.