DESERTIFICATION AND ANIMAL BIODIVERSITY IN THE DESERT GRASSLANDS OF NORTH-AMERICA

Studies of breeding birds and small mammals were conducted at a series of sites that form a gradient of severity of desertification. Desert grassland sites represented the least changed landscape units and mesq uite coppice dunes represented the most severe degradation, an irrever sibly degraded landscape unit. The hypothesis that desertification red uces species diversity was not supported by the data. Species richness and diversities (Shannon-Weaver H') of breeding birds were higher in the desertified areas than in the grassland with one exception. Data f rom a site dominated by the exotic African grass, Eragrostis lehmannia na, in south-eastern Arizona showed that breeding bird diversity was l ower at that site than at a site in the same region that was dominated by native grasses. Species richness, diversity (H'), and abundance of small mammals were also higher in desertified areas than in desert gr assland. Most grassland species of birds and mammals persist in the de sertified habitats and species that are characteristic of shrublands c olonize desertified desert grasslands. This accounts for the increases in species richness. However some species such as the banner-tailed k angaroo rat, Dipodomys spectabilis, are eliminated when grassland degr ades to mesquite coppice dune or eroded creosotebush communities. Thes e data suggest that other measures of faunal biodiversity such as Keys tone species may be better measures of the impact of desertification o n animal biodiversity. (C) 1997 Academic Press Limited.