A heterogeneidade de macrófitas aquáticas como preditor da estrutura espacial das assembleias de sapos em um Lago Amazônico

Abstract

Investigating the effects of environmental gradients on assemblage spatial structure is relevant to understand mechanisms and processes affecting biodiversity. Environmental gradients may act as ecological filters limiting species occurrence and abundance, which generates non-random patterns of habitat occupancy. Environmental filtering-mediated biodiversity emerges from relationships between environmental gradients and estimates of α- and β- diversity. Such relationships have been widely demonstrated in frog assemblages occupying forests in Amazonia but are rarely assessed in non-forest ecosystems such as macrophyte banks in lakes. Macrophyte banks may vary spatially in terms of width, height, and species composition, in response to physicochemical parameters of water. Therefore, it is reasonable to expect spatially heterogeneous frog assemblages in response to variation in habitat vertical stratification and perch shape. In this study we sampled 50 plots covering 15 km2 of continuous macrophyte banks to test the effects of distance from the lake bank, water depth, macrophyte height and composition (proportions of morphotype occupancy), pH, dissolved oxygen and temperature on frog α-diversity and β- diversity estimates. We found 16 species, for which local distribution was not random but characterized by α-diversity positively affected by macrophyte height, and β-diversity affected by macrophyte height and composition, and water depth. Our results suggest environmental filtering as a major factor structuring frog assemblages even in relatively small and regionally rare ecosystems. These findings are highly relevant to ecology and conservation because they suggest that aquatic macrophyte banks should be considered as distinct biogeographic units from adjacent habitats.