The Brazilian Caatinga in South American Zoogeography: Tropical Mammals in a Dry Region
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Recent research in S American biogeography on groups other than mammals suggests that the semi-arid caatinga of NE Brazil provided xeric refugia during mesic phases of the Pleistocene climatic cycles. The caatinga mammal fauna might therefore be expected to contain numerous species showing a pronounced level of adaptation to aridity and the origins of a substantial segment of the fauna should be traceable to the diversification and eventual speciation that would be expected to have resulted from extended isolation in a xeric environment. Analysis of the extant mammal fauna fails to corroborate these predictions; only one endemic mammal species is found, and the fauna lacks the expected physiological and morphological adaptations. Other vertebrate groups also exhibit low levels of endemism. A high degree of climatic unpredictability may preclude the development of a unique fauna adapted to xeric conditions. The present habitats avoid the environmental effects of aridity and climatic unpredictability during harsh periods by utilizing the numerous mesic enclaves scattered throughout the NE; even during periods of elevated precipitation, most mammal species reach their highest density in these relatively restricted areas. Although the caatinga contains a xeric-adapted flora, it harbours an anomalous mammal fauna that is more characteristic of a mesic tropical biome in terms of both species composition and overall adaptation.-from Authors
