Which environmental variables better explain changes in anuran community composition? A case study in the restinga of Mata de São João, Bahia, Brazil

Abstract

Most studies of amphibian communities are restricted to aquatic environments, which precludes sound descriptions of changes in composition throughout entire habitats. Moreover, few works focus on the environmental processes that shape the composition of these communities, particularly in tropical ecosystems. In this study, we investigated which environmental variables were able to predict the main changes in anuran community composition in a shrub-to-forest Restinga on the northeastern coastline of Bahia State, Brazil. In 30 plots (60 × 25 m) along a continuous Restinga area, we determined, over two consecutive rainy seasons, the abundances of anuran species and 20 primary environmental variables. We represented the main environmental gradients of the Restinga using the first axes derived from a principal component analysis (PCA) of the matrix of environmental variables. We represented the main changes in community composition using a synthetic axis built by applying the nonmetric multidimensional scaling technique (NMS) on the matrix of species abundances. We then evaluated, using a multiple linear regression test, which environmental gradients, if any, were able to explain changes in community composition. We recorded 737 anurans, belonging to 8 families, 17 genera, and 30 species. Five orthogonal environmental gradients were extracted, representing ca. 80% of the variance of the matrix of environmental variables; the first PC represented the covariation among the amount of leaves in the stratum from 6 to 10 m high, percentage of leaf litter, percentage of terrestrial bromeliads with direct sunlight, number of terrestrial bromeliads, and soil moisture. The NMS axis explained 50% of the variance of the abundance matrix and ordered the plots through the sequence (1) beach zone, (2) arboreal vegetation with temporary ponds and/or permanent lakes, (3) arboreal vegetation with rivers or streams, and (4) arboreal vegetation without bodies of water. Only PC1, which represented a shrub-to-forest gradient, was significantly related to the NMS axis. The change on plant communities, allied to soil moisture and type of water body, was the most important environmental factor acting on the structure of the anuran community herein studied.