Diversity Begets Diversity

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Science  20 Apr 2001:
Vol. 292, Issue 5516, pp. 399
DOI: 10.1126/science.292.5516.399d

There is huge geographical variation, especially between polar and equatorial regions, in the numbers of terrestrial plant and animal species. Ecologists have wrestled with a variety of competing hypotheses—energy availability, habitat heterogeneity, area, and geometric constraints being the major classes—to explain these patterns. Using detailed maps of species distributions and regression analyses with 16 independent variables, Rahbek and Graves investigate the correlates of species richness patterns in South American breeding birds, which constitute at least 25% of the entire bird fauna of the world, across a range of spatial scales. They find that topographic heterogeneity and two elements of climate, precipitation and cloud cover, are the most important predictors of regional species richness for birds: humid montane areas and adjacent regions are the most species-rich. There is a trough in species richness across central Amazonia, confirming that energy input and biome area are not primary determinants of species wealth. — AMS

Proc. Natl. Acad. Sci. U.S.A.98, 4534 (2001).

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