Temporal variation in the abundance and number of species of frogs in 10,000 ha of a forest in central amazonia, Brazil

Abstract

In this study we sampled diurnal and nocturnal anuran assemblages in 10,000 ha of tropical forest. We provide data on composition and variation in the occurrence and abundance of these species during two rainy seasons. Our study took place at Reserva Florestal Adolpho Ducke, Manaus, Amazonas state, Brazil. We analysed the anuran assemblage for three diurnal samples and five nocturnal samples from November/2002 to May/2004. Data were collected in 72 plots systematically distributed over a 64 km2 grid. Diurnal anuran assemblage surveys were conducted by visual encounter. We sampled the nocturnal anuran assemblage using standardized methods – simultaneous visual encounter surveys and auditory sampling. We detected 30 species of anurans, belonging to seven families using all methods and periods. A total of 6,030 individuals belonging to eight species and four families were recorded in diurnal samples and 25 species (16,050 individuals), belonging to six families were recorded in nocturnal samples. The number of nocturnal species varied from 18 in the beginning of the second rainy season to 22 in the middle of the rainy season. Fourteen species were found in the five sampling periods. The species with high abundance that were widely distributed in the study area were those with reproductive specializations such as direct development, development in terrestrial nests, or development in bromeliads with parental care. This study showed the viability of the system of surveys and the methods used for sampling anuran assemblages in a tropical forest. They were also adequate for estimating the richness and abundance of species. However, systematically distributed plots, such as those used in this study, mostly reveal terrestrially breeding frogs. The aquatic-breeding frogs were found mainly in riparian zones and were rare in zones distant from water bodies. There were a low number of plots around water bodies (25%) which, consequently, reduced the record of aquatic-breeding individuals.