Padrões de distribuição e abundância de anuros em 64 km2 de floresta de terra-firme na Amazônia Central

Abstract

The objective of this study was to evaluate the distribution of anuran species and their relationships with biotic and abiotic variables in 72 permanent plots, located across 64 km2 in the Adolpho Ducke forest reserve, Manaus, AM. In each plot, I determined species richness and individual species’ abundances using three diurnal samples (visual sampling with litter removal) and five nocturnal samples (visual and auditory samplings) during two rainy seasons (between 2002 and 2004). I examined the relationship of the anuran species to five biotic and abiotic variables: slope, edaphic factors (clay proportion and pH), number of trees, leaf-litter volume, and drainage basin. In order to facilitate interpretation of my results, I classified the anuran species into assemblages according to activity period (diurnal or nocturnal) or tadpole development (terrestrial or aquatic). During my study, I found a total of eight diurnal frog species across the study plots, of which seven were detected during the three diurnal samples. I registered a total of 24 nocturnal species across the study plots, all during the nocturnal samples. These 24 nocturnal species represent 72 % of the nocturnal anurans known to occur in the reserve. I found eight nocturnal species to be rare, or detected in only 1-5 study plots (Epipedobates femoralis, Hypsiboas geographicus, H. lanciformis, Phyllomedusa bicolor, P. tarsius, P. tomopterna, Leptodactylus mystaceus, and Lithodytes lineatus). Overall, plots had greater species richness during the middle of the rainy season and higher species’ abundances during the beginning of the rainy season. Soil texture, slope and pH influenced the distribution of the terrestrial anurans. However, these relationships were subtle and I found that the majority of these species occurred across the entire gradient of soil texture, found on our study sites. I found stronger relationships between these three abiotic variables and the distribution of the smaller species of terrestrial anurans, Colostethus stepheni, Adenomera andreae and Eleutherodactylus spp. Drainage basin did not affect the distributions of the terrestrial species. I found a relationship between soil texture and the distributions of aquatically-reproducing species. However, in the study area, soil texture is correlated with stream location; clay content decreases in low-lying areas, such as near stream beds. So this result suggests that I detected more aquatic species in areas near streams or temporary ponds. Drainage basin influenced the distributions of four aquatically-reproducing species. Three species, Atelopus spumarius, Colostethus sp., and Leptodactylus rhodomystax, were restricted to one of the two drainage basins in our study area and the abundance of one species, Cochranella oyampiensis, was significantly different between basins. Predictive models including edaphic factors and habitat structure variables are important predictors of habitat relationships at a large scale and may interact to influence habitat at smaller spatial scales. Edaphic and topographic data can be used to identify areas of high conservation value in central Amazonia.