Padrões de distribuição de anuros em uma área de 25 Km² em uma floresta sazonalmente alagável no norte da Amazônia brasileira

Abstract

Recent studies on arboreal and leaf litter anuran assemblages suggest that the variation in assemblage composition explained by environmental parameters is only of minor importance. In contrast, for anuran assemblages of streams habitat heterogeneity, spatial effects and spatially structured environments were considered relevant. Therefore, we investigated the patterns of distribution of anurans in an area of 25 km2 in a seasonally flooded forest situated in the Viruá National Park (Roraima state, Brazil) in Northern Amazonia. We analyzed environmental variables potentially capable of predicting anuran assemblage structure and composition in relation to environmental gradients in 30 plots evenly distributed over a 5x5km area. Environmental variables with a significant effect in all plots were soil texture and altitude. For plots subject to flooding we included water cover in the analysis. We determined the abundance of each species based on three periods of sampling during the rainy season (June, July and August 2009). The variation in species composition among plots was synthesized in two axes using Nonmetric Multidimensional Scaling (NMDS) with the matrix of abundance and occurrence of the species. We used multiple regression analysis to test for variables that were capable of explaining the variation in species composition. We found 3339 individuals, representing 19 species and 5 families. Most species were found at the beginning, and most individuals were found in the middle of the rainy season. Dendrosophus sp. was the most abundant species, and Osteocephalus aff. taurinus was the least abundant. Dendropsophus sp., Hyspiboas sp., and Leptodactylus aff. andreae accounted for 63.8% of all individuals found in the plots. The first and second axes of the NMDS organized the plots along the gradient of soil clay content. Canopy openness, herb cover, soil sand content, slope and number of trees on the plots were correlated with soil clay content and, therefore, also explained the variation in the assemblage composition. Considering only the plots subject to flooding, soil clay content was also the major environmental factor, leading to important habitat heterogeneity, responsible for the anuran assemblage structure in the Viruá National Park. The results are not only of ecological interest but also of practical significance for the conservation of anurans in flooded tropical forests.