Author
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Whitford, Walter |
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Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/21/1997 Publication Date: N/A Citation: N/A Interpretive Summary: In a gradient of landscapes ranging from desert grasslands (least changed) to coppiced mesquite dunes (most severely desertified) we studied bird and small mammal diversity to test the hypothesis that desertification reduces species diversity. In all but one instance there were more species of breeding birds in degraded areas than in grasslands. The number of species and abundance of small mammals also was higher in desertified areas rather in grasslands. This may be because grassland species remain in areas that become degraded and are joined by species that prefer desertified areas. However, some species such as the banner-tailed kangaroo rat are eliminated when grasslands become desertified. Thus, measures of biodiversity are not the best measures of the impact of desertification. Technical Abstract: 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 unit and mesquite coppice dunes represented the most severe degradation, an irreversibly degraded landscape unit. The hypothesis that desertification reduces 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 from a site dominated by the exotic African grass, Eragrostis lehmanniana, in south-eastern Arizona showed that breeding bird diversity was lower 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 grassland. Most grassland species of birds sand mammals persist in the desertified habitats and species that are characteristic of shrublands colonize desertified desert grasslands. This accounts for the increases in species richness. However, some species such as the banner-tailed kangaroo rat, Dipodomys spectabilis, are eliminated when grassland degrades to mesquite coppice dune or eroded creosotebush communities. These data suggest that other measures of faunal biodiversity such as keystone species may be better measures of the impact of desertification on animal biodiversity. |
