Mammals in South American drylands: faunal similarity and trophic structure

We compared the fauna of small mammals (less than 500 g body weight) among five major South American drylands (Atacama, Altiplano, Monte, Patagonia an d Caatinga) and found considerable heterogeneity and distinctiveness in spe cies richness and composition between these biomes. From a total of 89 reco rded species, 76 of them are restricted to only one of these drylands. The highland desert, or Altiplano, is the biome with the highest number of spec ies. Despite the marked differences in the composition of the mammalian fau na, the trophic structure shows a rather consistent pattern: herbivores are the most important trophic group in all drylands. This consistency seems t o be more the result of phylogenetic inertia than of similar ecological pro cesses. Our results are compared with recent studies on desert small mammal s across continents.