On the relative importance of history and ecology in structuring communities of desert small animals

Several recent studies have compared small mammal community structure acros s multiple deserts on different continents. These studies have tacitly assu med that variation in community structure was greater between continents th an within, and so have nor evaluated variation across desert regions within continents. I evaluated several metrics of community structure and a model of community assembly for four desert regions in North America - the Great Basin: Mojave, Sonoran, and Chihuahuan Deserts - in order to explicitly co mpare these metrics across these deserts. Additionally, I compared these re sults with similar analyses conducted on two desert regions in central Asia - the Gobi Desert and the Turan Desert Region - to evaluate th; relative m agnitude of intra- vs inter-continental variation. Although the patterns ob served are complex, they demonstrated marked heterogeneity in desert small mammal communities within North America. However, this heterogeneity is muc h less than that observed in inter-continental comparisons, in which Asian and North American deserts differ markedly. These results agree with other recent studies providing limited or no support for the existence of substan tial convergence in community characteristics or ecological function across geographically distant regions. Rather, the results support thr hypothesis that the common evolutionary history of faunas in globally disjunct landma sses has had a. stronger influence on the evolution of communities and faun as than do regional variations in climate, physiography. etc. Whereas a com mon ecological setting may have large impacts on some Facets of organismal structure (e.g., bipedalism in desert small mammals). common evolutionary h istory appears to have a more profound influence on local dynamics.