The most thorough compendium of comparative data on grassland biodiversity comes from the World Conservation Monitoring Centre (WCMC) (1992), which assembled data from a wide variety of sources to achieve preliminary, working comparisons both of grasslands on different continents and grasslands with other types of ecosystems, WCMC (1992) estimated that only 5% of the world's bird species and 6% of the mammal species were primarily grassland-adapted, since many of the species with abundance centers in grasslands also range over broad geographic areas and utilize a variety of different ecosystem types. Still, the grasslands of Africa are major biodiversity locations for large grazing, browsing and predatory mammals, and many birds that breed in Eurasia winter in African grasslands (Williams 1963). Mares (1992), in a provocative paper entitled "Neotropical mammals and the myth of Amazonian diversity" documented that the drylands of South America have a more diverse mammalian fauna than any of the other major South American ecosystem-types, including tropical rainforest, particularly when considering endemic mammal species. As Redford et al. (1990) observed in relation to threats to the South American Chaco, "The concentration on rainforests. . . has led to the neglect of other severely threatened ecosystems." Chief among those regions are grasslands.
The WCMC (1992) ranked the Earth's natural grasslands in the following order of decreasing importance as repositories of biodiversity of indigenous plants and animals: African savanna; Eurasian steppe; South American savanna; North American prairie; Indian savanna; Australian grassland. Surprisingly, the plant species density of African savanna grasslands in regional geographic blocks is not far below that of African rainforest (Menaut 1983). At present, of course, there are very few, if any, surviving primary grasslands in India, and much of those elsewhere have been converted to other land-uses.
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