Convergent evolution of desert rodents: multivariate analysis and zoogeographic implications

Abstract

Ecological investigations were conducted on rodent faunas in the Sonoran Desert of the southwestern United States and the Monte Desert of northwestern Argentina. Both study areas are physiognomically quite similar and the rodents are only distantly related. Such conditions are ideal for an assessment of possible evolutionary convergence. Multivariate analyses of morphoecological characters support the subjective interpretation that ecological equivalents between the deserts differ in their degree of similarity. The data indicate that the Monte rodent fauna is composed of two distinct groups: a) the caviomorph rodents, which are highly desert adapted; and b) the murids, which range widely beyond the desert's boundaries and are probably not as highly desert adapted, as a group, as are the caviomorphs. When the Monte and Sonoran faunas are compared with a North American coniferous forest rodent fauna, data show that both desert groups have converged toward one another. The different degrees of desert adaptation and different distributional patterns indicate that the Monte Desert was colonized in two different periods (one in the early Tertiary and one in the late Pliocene or early Pleistocene) and can be interpreted as supporting theories regarding South America's colonization by mammals which were first proposed by Simpson (1951).