Padrões de distribuição e abundância de anuros em áreas ripárias e não ripárias de floresta de terra firme na reserva biológica do Uatumã - Amazônia central

Abstract

Most studies conducted with communities of frogs are restricted to aquatic environments used for breeding, such as puddles and streams, what precludes describing the species distribution along environmental gradients that exist in the area as a whole. In this study, we investigated possible patterns of species distribution in a 25 km2 area at the Uatumã Biological Reserve, central Amazonia, testing which environmental variables were able to predict changes in anurans communities. We describe the composition of species of frogs and their relations with environmental variables in 45 plots of 250 m in length, from which 30 plots were evenly distributed in the whole area and 15 plots demarcated only on the banks of streams. The environmental variables analyzed in those plots distributed in the whole area were distance of streams, soil clay percentage, altitude and tree density. In the riparian plots were analyzed stream size, speed and flow, floodplain width and altitude. We determined the abundance of each species based on three night samples, in each plot, taken during one rainy season (nov/dez2008; jan/fev2009; abr/mai2009). We represented changes in species composition between the plots by using a synthetic axis produced by non-metric multidimensional scaling (NMDS), a presence and abundance species matrix sorting method. Then, using linear regression analysis, we assessed which variables were able to explain the variations in species composition. We found 10,727 individuals belonging to 59 species of 11 families. Most species were found by the beginning of the rainy season, as most specimens were registered by middle- and end-season. Pristimantis fenestratus was the most common species, followed by Osteocephalus oophagus, Hypsiboas fasciatus and Leptodactylus andreae. By visual recognition only the most common species was Atelopus spumarius, followed by Rhinella proboscidea e Ameerega hahneli. Analyzing those evenly distributed plots in the area, the NMDS axis 1 ranked the plots according to a stream distance gradient, that begins at the riparian areas, through the intermediate areas and reaching the plateaus areas. Stream distance to the plot, altitude, clay percentage, and tree density were correlated and used to explain changes in community composition. By only analyzing plots located on the banks of streams, changes in communities composition occured in a gradient that ranged from high speed streams and small floodplain area to slow speed streams with extensive floodplain area. The results of this study indicate a strong influence of environmental factors that determine the structure of frog communities, whether by analyzing the area as a whole, or analyzing only its riparian parts. The occurrence of preferred habitats for some species has, beyond its ecological significance, a practical meaning for these species management and conservation.