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<p>The relative importance of environmental selection, dispersal, and demographic stochasticity in structuring aquatic communities remains poorly resolved, especially in human-impacted Neotropical regions. Using diatoms, we assessed how local environmental conditions, catchment land use, and spatial factors shape community richness and composition in subtropical streams, and whether responses differ among common, rare, and very rare species. Diatoms were sampled in 50 streams of the Ibicuí river basin (Pampa biome, Brazil). Species were identified and categorized as common, rare, or very rare based on abundance quartiles. We measured local variables, land use, and spatial predictors (PCNM). Richness was modeled by multiple linear regression, while composition was analyzed via pRDA and variation partitioning. Local environmental variables were primary predictors of species richness across all groups, with canopy openness as a key filter. Conversely, community composition showed a strong spatial signature for the total assemblage and common species, where PCNM accounted for most variation; land use effects were minimal. The composition of rare species was explained only by water velocity, while very rare species were structured exclusively by fine-scale spatial predictors. These results indicate that metacommunity structuring mechanisms for benthic diatoms in the studied streams depend on the evaluated attribute and species rarity. Environmental gradients govern richness in all groups, but spatial processes dominate compositional changes, especially for common and very rare taxa. Rare species are filtered by hydrodynamic conditions, whereas very rare species reflect spatial configuration more than the measured environmental gradients. This study integrates multi-scale predictors and explicitly separates species by rarity, clarifying metacommunity organization in subtropical grassland streams. Ultimately, our findings suggest that diatom species rarity should be considered for effective biomonitoring and biodiversity conservation strategies in subtropical grassland streams.</p>

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Common and rare stream diatoms respond differently to local, catchment and spatial drivers

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年8月4日

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  • Maria Gabrielle Rodrigues-Maciel,
  • Ana Paula Tavares Costa,
  • Isabela Menezes Pinzón,
  • Claudio Rossano Trindade Trindade,
  • Ricardo Hideo Taniwaki,
  • Fabiana Schneck

摘要

The relative importance of environmental selection, dispersal, and demographic stochasticity in structuring aquatic communities remains poorly resolved, especially in human-impacted Neotropical regions. Using diatoms, we assessed how local environmental conditions, catchment land use, and spatial factors shape community richness and composition in subtropical streams, and whether responses differ among common, rare, and very rare species. Diatoms were sampled in 50 streams of the Ibicuí river basin (Pampa biome, Brazil). Species were identified and categorized as common, rare, or very rare based on abundance quartiles. We measured local variables, land use, and spatial predictors (PCNM). Richness was modeled by multiple linear regression, while composition was analyzed via pRDA and variation partitioning. Local environmental variables were primary predictors of species richness across all groups, with canopy openness as a key filter. Conversely, community composition showed a strong spatial signature for the total assemblage and common species, where PCNM accounted for most variation; land use effects were minimal. The composition of rare species was explained only by water velocity, while very rare species were structured exclusively by fine-scale spatial predictors. These results indicate that metacommunity structuring mechanisms for benthic diatoms in the studied streams depend on the evaluated attribute and species rarity. Environmental gradients govern richness in all groups, but spatial processes dominate compositional changes, especially for common and very rare taxa. Rare species are filtered by hydrodynamic conditions, whereas very rare species reflect spatial configuration more than the measured environmental gradients. This study integrates multi-scale predictors and explicitly separates species by rarity, clarifying metacommunity organization in subtropical grassland streams. Ultimately, our findings suggest that diatom species rarity should be considered for effective biomonitoring and biodiversity conservation strategies in subtropical grassland streams.