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

Several recent studies have compared small mammal community structure across multiple deserts on different continents. These studies have tacitly assumed that variation in community structure was greater between continents than within, and so have not 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 compare these metrics across these deserts. Additionally. I compared these results with similar analyses conducted on two desert regions in central Asia - the Gobi Desert and the Turan Desert Region to evaluate the relative magnitude of intra- vs inter-continental variation. Although the patterns observed are complex, they demonstrated marked heterogeneity in desert small mammal communities within North America. However, this heterogeneity is much 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 substantial convergence in community characteristics or ecological function across geographically distant regions. Rather, the results support the hypothesis that the common evolutionary history of faunas in globally disjunct landmasses has had a stronger influence on the evolution of communities and faunas than do regional variations in climate, physiography, etc. Whereas a common ecological setting may have large impacts on some facets of organismal structure (e.g., bipedalism in desert small mammals), common evolutionary history appears to have a more profound influence on local dynamics.