Community Structure in High Andean Herpetofaunas

Abstract

Density, diversity, niche breadth and niche overlap were obtained and analyzed for amphibians and reptiles in 10 study sites above tree line in the Andes. Two to eight species were found at each site; a total of 1373 specimens of 33 species was studied. Species richness shows no clear latitudinal trends; there is a trend for increasing species richness in reptiles from equatorial to temperate sites, and there is a greater richness of amphibians in the equatorial sites. Two niche dimensions were analyzed-structural habitat and food. Niche breadth values for structural habitat are essentially the same in reptiles and in amphibians. Niche breadth values for food are higher in amphibians than in reptiles. Overall niche breadth is slightly higher in amphibians than in reptiles. Niche overlap for structural habitat is higher than that for food. Overlap values between any pairs of species at the same site are generally low, with the exception of some pairs of amphibians in which values are relatively high. However, there is no consistent difference in values within and between communities. Niche overlap increases with decreasing species richness and species diversity. Compared with the adjacent lowlands, the herpetofauna of the high Andes is depauperate, and at any one locality the fauna seldom exceeds eight species. Furthermore, the Andes extend as an essentially unbroken mountain chain through 60' of latitude from the tropics to cool temperate regions. Thus, it is possible to study the relatively simple high montane communities along a latitudinal gradient. We are concerned here with communities of amphibians and reptiles that occur above tree line-principally in habitats commonly known as pdramo andpuna, but areas of Patagonian scrub are included in the southern Andes. Data on biomass, life histories, and geographical distributions will be presented elsewhere. This content downloaded from 157.55.39.143 on Wed, 15 Jun 2016 06:19:52 UTC All use subject to http://about.jstor.org/terms 46 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCES In the analysis of these small communities, we posed the following questions: 1) What is the composition of the Andean herpetofaunal communities, and how does the composition change geographically? 2) How are various resources used within communities, and how does the use change with different species composition? 3) What kind of relationship exists between species richness and niche breadth within a community? 4) What kind of relationship exists between species richness and niche overlap within a community? 5) Is niche overlap greater among pairs of allopatric species than among pairs of sympatric species? Finally, we attempt to place the quantitative analyses within a naturalistic perception of the communities.