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Patterns of Species Diversity in Anuran Amphibians in the American Tropics

William E. Duellman
Annals of the Missouri Botanical Garden
Vol. 75, No. 1 (1988), pp. 79-104
DOI: 10.2307/2399467
Stable URL: http://www.jstor.org/stable/2399467
Page Count: 26
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Patterns of Species Diversity in Anuran Amphibians in the American Tropics
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Abstract

The Neotropical Region has a greater species richness of anuran amphibians than any other region in the world. Approximately 44% of the total number of species of anurans of the world (3,533) occur in the American tropics, and many new species are discovered every year. Patterns of species diversity were determined by analyzing data from 48 sites-32 in the lowland tropics (11 Middle American, 21 South American), nine in montane cloud forests (four Middle American, five South American), and seven in supra-treeline regions of the Andes. Taxa also were noted as to their reproductive mode (site of egg deposition, site of larval development, and associated parental care, if any). As expected, for the entire anuran fauna, there are gradients from lower diversity in dry regions to higher diversity in wet regions, and from lower diversity at high elevations to higher diversity at low elevations. The greatest species diversity is in the equatorial region of the upper Amazon Basin. However, different patterns emerge when taxonomic groups (families, subfamilies, and large genera) are examined independently. Two factors contribute significantly to the different patterns observed: (1) the historical biogeography of different taxa, especially in relation to the separation of Central America from South America during most of the Cenozoic, and (2) reproductive modes of the taxa. Seventeen reproductive modes can be identified among anurans at the 48 sites. The generalized reproductive mode (eggs and tadpoles in lentic water) is characteristic of all lowland sites but is rare or nonexistent in montane regions where there are few ponds. Some reproductive modes involve terrestrial eggs and/or larvae that are dependent for their survival on high moisture content of the air; anurans having these modes are most diverse in regions having high humidity. Other modes necessitate the presence of high-gradient streams or aerial aquatic habitats (bromeliads) for the development of eggs and tadpoles. Sites having the highest species diversity also have the greatest diversity of reproductive modes; these sites are in lowland rainforest near the base of the Andes and in the Atlantic forest of southeastern Brazil at the edge of the Brazilian Highlands. Thus, although total species diversity in anurans is dependent on rainfall, patterns of diversity of component groups results partly from their geographic histories and partly from the consequences of the nature of their reproductive modes.

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