Structuring factors of beta diversity in metacommunities of semiaquatic bugs in the central Amazon Basin

Beta diversity provides important insights into the deterministic and stochastic processes that shape biological communities. Gerromorpha, semiaquatic insects commonly found in Amazonian streams and rivers, are particularly well suited for investigating these mechanisms because they respond to both environmental gradients and constraints imposed by hydrological connectivity. In this study, we evaluated how environmental and spatial variables structure Gerromorpha beta diversity in streams of the Central Amazon. We sampled communities across four Amazonian sub-basins and collected environmental, spatial, and biological data. Beta diversity was quantified using local contributions to beta diversity (LCBD) based on abundance data (LCBD ab ), presence–absence data (LCBD pa ), and species contributions to beta diversity (SCBD). We then assessed the relationships between LCBD ab and LCBD pa and local environmental and spatial characteristics, as well as between SCBD and species attributes, including abundance, occupancy, niche breadth, and niche position. LCBD ab was mainly explained by spatial structure, represented by multiple spatial axes, whereas LCBD pa was primarily related to environmental variation, especially the Habitat Integrity Index (HII). Species with high abundance but low occupancy contributed more strongly to SCBD, as did generalist species with non-marginal niche positions. Overall, our results indicate that beta diversity in Gerromorpha metacommunities is jointly shaped by environmental filtering and dispersal limitation, with these processes influencing species abundances and occurrences in distinct ways. Maintaining environmental integrity and connectivity among sites is therefore crucial for preserving regional compositional variation and preventing biotic homogenization in Gerromorpha metacommunities.