TEMPORAL CHANGES IN A CHIHUAHUAN DESERT RODENT COMMUNITY

We used time series analysis of ten years of monthly census data to assess the responses of both individual species and an entire community of rodents to a fluctuating desert environment. Autocorrelation analysis revealed different patterns of intra-annual fluctuation among the 11 species: Dipodomys spectabilis and Perognathus flavus had pronounced annual cycles; D. ordii, D. merriami, Chaetodipus penicillatus, Onychomys torridus, O. leucogaster, and Neotoma albigula exhibited annual cycles modified by interannual variation; and Peromyscus eremicus, Pm. maniculatus, and Reithrodontomys megalotis showed little evidence of annual periodicity. The timing af annual cycles and the pattern of inter-annual fluctuations also differed among species. However, two results suggest that several species responded similarly to long-term environmental variation: 1) population densities of four species and total rodent biomass and numbers were positively correlated with the densities of annual plants; and 2) many pairs of species exhibited positively correlated population dynamics over the ten years. Clustering of pairwise cross-correlation coefficients was used to identify sets of species with similar population dynamics. These clusters did not necessarily contain closely related or ecologically similar species. Detrended Correspondence Analysis identified three independent patterns of variation in species composition: a long-term trend; a four- to five-year repeated pattern that appeared to correspond to the climatic effects of the El Nino Southern Oscillation; and an annual cycle. In general, species appeared to respond individualistically to environmental variation. There was no evidence of an equilibrium community composition or of alternative stable configurations. Some competing species had negatively correlated population dynamics, but the majority of competitors exhibited positive correlations that apparently reflected similar responses to fluctuating resources.