Contribution of environmental variables to anuran community structure in the Caatinga Domain of Brazil

To ascertain the influence of environmental variables on thestructure of anuran communities, we conducted tests to determine which variables best explain the spatial distribution patterns of different communities of anurans in a rocky, montane environment characterized mainly by open habitats and gallery forests. The studyarea is the Sete Passagens State Park in the State of Bahia, Brazil, an area included in the Chapada Diamantina Region and in the Caatinga Morphoclimatic Domain. We sampled 20 plots (60 × 25 m) during two rainy seasons, and measured 13 environmental variables. The environmental matrix was reduced to four synthetic axes through the principal component analysi, and the anuran community matrix was reduced to a synthetic axis through the nonmetric multidimensional scaling method. We tested the association between environmentalaxes (independent variables) and community composition (dependent variable) using a multiple regression analysis. The single axis significantly associated with the species of anurans found in any given plot is Principal Component 1, in which the major contributorsto variation are factors involving vegetation structure, listed in descending order, as follow: percentage of leaf litter, density of trees, canopy height, soil moisture, and percentage of understory, shrub, and herb layers. The ordination of the anuran communityshowed an environmental gradient from the Campo Rupestre to Semi-deciduous Forest patches, characterized mainly by the gradual increase of layering in the vegetation.