Uma questão de escala: Fatores históricos e ambientais estruturam assembleias de anuros diurnos do Alto Rio Madeira

Abstract

Biogeographical history and current ecological interactions have usually been addressed separately to explain patterns of biodiversity. In this study, we evaluated the integrated effects of biogeographical and environmental factors in structuring the diurnal amphibian anuran assemblages of the upper Madeira River, southwestern Amazonia. We used a sampling design involving 98 standardized units, distributed across seven locations covering both banks of the river’s course in the state of Rondônia, Brazil. An active search for frogs was performed in three campaigns between February 2010 and February 2011, with the objectives of: 1 ) evaluate the effect of the Madeira River as a biogeographic barrier at the species assemblage level, and 2 ) test the influence of seven environmental variables (vegetation structure, vegetation cover, soil nutrients, soil structure, slope, altitude and distance from the river bank) on the spatial structure of the frog assemblages, separately by river bank. Thirteen species of diurnal frogs were recorded, six of which were restricted to one of the river margins. Multivariate analysis of variance indicated a significant effect of the river as a barrier. Multiple regression analyzes suggested that the environmental variables structuring frog assemblages differ on either side of the river. We found that both historical elements (on a regional scale) and environmental actors (at a local scale) shaped the occurrence and distribution of frog species in the study area.