Environmental filtering and limiting similarity shape the taxonomic and functional diversity of amazonian floodplain frogs across pasture–edge–interior gradients

Forest edges shape biotic assemblages in deforested landscapes by altering microclimatic conditions and imposing ecological filters that constrain species responses based on functional traits. Understanding these edge effects is critical for developing effective conservation strategies in tropical regions undergoing rapid agricultural conversion. We investigated how anuran assemblage structure, taxonomic diversity, and functional diversity vary across pastures, forest edges, and interiors in Amazonian floodplain forests, which face high levels of disturbance due to recent land use changes. We surveyed frog assemblages across pasture-edge-interior gradients, assessed taxonomic and functional diversity using five indices, classified species into functional and edge response groups, and evaluated relationships with local environmental and landscape variables. We also examined correlations between species richness and functional diversity indices across habitats. Assemblage structure differed significantly among habitats due to loss of rare forest-restricted species, with changes linked to edge proximity, substrate temperature, light intensity, and perch height. Taxonomic and functional diversity responded to landscape connectivity, leaf litter depth, and humidity rather than edge distance alone. Critically, functional groups failed to predict species' edge responses, revealing a decoupling between functional classification edge associations. Correlations between richness and functional diversity varied across habitats, with strong positive correlations in forest edges and interiors, and weak or negative correlations in pastures, suggesting environmental filtering in pastures and limiting similarity in forest interiors as dominant assembly mechanisms. Forest edges act as ecological filters, limiting the colonization of pasture species into forest interiors through environmental gradients and competitive interactions with functionally analogous forest species. Our findings emphasize the importance of integrating edge buffer design with landscape-scale connectivity planning, prioritizing the maintenance of forest fragment connectivity and microhabitat thresholds over reliance on buffer width standards alone.