Assessing Site and Species Associations With Beta Diversity of Fish Assemblages in Amazonian Streams

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ABSTRACT The increasing environmental changes threatening the fish fauna of streams are driving a growing interest in understanding how sites and species contribute to diversity, as this is important information for decision‐making related to the management and conservation of priority areas and species. The objective of this study was to understand how environmental factors, spatial distance between streams, land use, and land cover (landscape) may be associated with the uniqueness of fish assemblages in Amazonian streams. We sampled fish assemblages and characterised environmental conditions in 29 streams within and around the Tapajós River basin, near the Amazon National Park in Brazil. Each stream was studied along a 150‐m stretch. The variables associated with the local contribution to beta diversity (LCBD) were vegetation cover and the presence of refuges. Streams inside and outside the park showed similar contributions to beta diversity. Species richness and abundance showed a negative relationship with LCBD, suggesting that unique sites tended to have few species and low abundance. The species that contributed most to beta diversity (SCBD) had intermediate occurrence, high abundance, and non‐marginal niches. We did not observe an effect of niche breadth on SCBD, as both generalist and specialist species contributed equally to beta diversity. Our findings underscore the role of environmental variables in ecological uniqueness. Sites unique in species composition may also exhibit low species richness and abundance. Our study demonstrates the importance of environmental variables in conserving biodiversity in Amazonian streams in the face of environmental changes. By examining the contributions of sites and species, we highlight the importance of considering habitat quality and uniqueness in protecting these ecosystems against the challenges of global change.