. Biology of the Heteromyidae. Heteromyidae. PANDESERTIC RODENT ECOLOGY 667 1982a, 1982/7, 1982c 1982^, 1982c 1982/; Willig and Mares, 1989). The region con- tains few endemics and those species that do persist in the area undergo marked pop- ulation reductions during dry periods. Per- sistence of most species occurs because they inh' .it mesic microhabitats limited to gra- nitic outcroppings that form hills and mesa- like structures. Such areas support green vegetation during the driest periods and, be- ing both extensive and widely distributed throughout the Caatinga, act as mesic re- fugia
. Biology of the Heteromyidae. Heteromyidae. PANDESERTIC RODENT ECOLOGY 667 1982a, 1982/7, 1982c 1982^, 1982c 1982/; Willig and Mares, 1989). The region con- tains few endemics and those species that do persist in the area undergo marked pop- ulation reductions during dry periods. Per- sistence of most species occurs because they inh' .it mesic microhabitats limited to gra- nitic outcroppings that form hills and mesa- like structures. Such areas support green vegetation during the driest periods and, be- ing both extensive and widely distributed throughout the Caatinga, act as mesic re- fugia for most species. Almost all species of Caatinga mammals are shared with the neighboring Cerrado grassland biome, a more mesic savanna woodland that occupies upland plateau ar- eas of central Brazil (Mares et al., 1985/?; Mares et al., 1989). As many as 10 species of small mammals are found in the Caatinga proper, but most are ground-dwelling or scansorial herbivores, micro-omnivores, or insectivores. Like the Chaco, no heteromyid equivalents inhabit the region. Australia Australia is essentially a desert continent, with 55% (or million square kilometers) of the continental land area being desert or semidesert habitats (Beadle, 1981; Mab- butt, 1984; Williams and Calaby, 1985). The paleohistory of the Australian continent is fascinating. Once connected to the Antarc- tic land mass and thence to South America and the remainder of Gondwanaland (in the Cretaceous, 115 million years ago, Norton and Sclater, 1979), the continent underwent great climatic and vegetational changes as it moved via sea floor spreading to its pres- ent position ( Raven and Axelrod, 1972; Specht, 1981a). Because it is now astride 30°S latitude, and because the continent is largely free of extensive mountainous areas to act as barriers to the prevailing westerlies, its deserts are of the subtropical type (Lo- gan, 1968), with diverse substrates and hab- itats ( Beard, 1984;Mabbutt, 1984; Wil-
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