Taxonomic replacement, but functional stability: taxonomic-functional decoupling in Amazonian streams from an Indigenous territory

Biodiversity patterns in tropical freshwater ecosystems remain unevenly understood, particularly in high-integrity regions such as Indigenous territories. In this study, we assessed taxonomic and functional beta diversity of Ephemeroptera, Plecoptera, and Trichoptera (EPT) in Amazonian streams located within the Panara Indigenous Territory, Brazil. We evaluated the relative contributions of local environmental variables, spatial processes, and landscape context to beta-diversity patterns. We disentangled the roles of replacement and richness differences across taxonomic and functional dimensions. EPT larvae were sampled in 31 streams during the dry season. Beta diversity was quantified using Sorensen-based dissimilarity indices, and functional dissimilarity was calculated from seven ecological traits using Gower distances. Taxonomic beta diversity was dominated by genus replacement and was jointly structured by local habitat variables and spatial components, indicating the combined influence of environmental filtering and dispersal limitation. In contrast, functional beta diversity was higher than taxonomic beta diversity and was predominantly structured by richness differences, with significant effects of local environmental variables but no detectable influence of spatial processes. This pattern indicates a decoupling between taxonomic and functional dimensions, suggesting high levels of functional redundancy among EPT genera across streams. Our findings demonstrate that Amazonian streams within Indigenous territories provide key systems for understanding community assembly processes under low levels of direct anthropogenic disturbance. By revealing contrasting mechanisms underlying taxonomic and functional beta diversity, this study underscores the importance of integrating multiple facets of biodiversity and reinforces the role of Indigenous territories as strategic landscapes for safeguarding Amazonian freshwater biodiversity.