Species diversity patterns in some present and prehistoric rodent communities.

Comparisons of prehistoric (A.D. 1100-1400) and extant cricetine-dominated rodent faunas from two locations in New Mexico and one in Arizona reveal temporal changes in both species diversity and taxonomic composition. The archaeological context of the prehistoric faunas permitted them to be dated rather accurately; paleoenvironmental inferences generated from other materials recovered in the excavations such as pollen samples, agricultural remains, and tree-ring specimens provided evidence about prehistoric environmental conditions in the study areas. Both richness and evenness components of diversity are lower in the present day faunas than in their prehistoric counterparts. At the beta (between-habitat or valley-wide) level of diversity the increased prehistoric species richness as well as the nature of the differences in present and prehistoric taxonomic composition can be accounted for by small climatic shifts which were occurring between A.D. 1100 and 1300 in the Southwest and the resultant biogeogrphic responses of certain rodent species. Alpha (or within-habitat) diversity is similar for all analyzed faunas. This suggests basic similarities in very local species packing despite observed spatial and temporal variation in valley-wide diversities. Environmental changes stemming from climatic shifts provide a reasonable explanation of the observed patterns of rodent species occurrence and diversity. Habitat destruction resulting from agricultural practies of prehistoric human populations appears to have had only a limited impact on these rodent communities.