Environmental filtering and dispersal limitation are essential processes affecting the variability of ecological communities. However, their relative contributions are highly debated and remain largely unknown in several systems, such as the hyperdiverse Amazon Basin. We determined the relative role of local, catchment, spatial, and biogeographical variables on the taxonomic and functional alpha and beta diversity of stream fish. We sampled 54 streams across six river basins in the Amazon. For each stream, we obtained 35 local habitat variables and 11 climate-catchment variables. Watercourse distances and basin identity were converted into spatial and biogeographical variables, respectively. We found that taxonomic alpha diversity responds both to spatial and local predictors, whereas its functional counterpart was mainly associated with local variables. Biogeography was the main factor structuring taxonomic and functional beta diversity, with a secondary contribution of catchment and local variables. Locally, substrate type and isolation determined the number and relative abundance of species and traits. The shared variation between biogeographical and environmental variables, especially altitude and slope, were strongly associated with beta diversity patterns, indicating a joint role of habitat filtering and dispersal limitation. Our results show the need to include both spatial and environmental variables in studies of stream communities at large spatial scales, as they are related to distinct processes that regulate community structure. We also encourage future studies to account for the responses of multiple facets of biodiversity to different drivers, as they provide essential and complementary information for community ecology and biogeography.

中文翻译：

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亚马逊河鱼分类和功能多样性的解开模式

环境过滤和扩散限制是影响生态群落变异性的重要过程。然而，它们的相对贡献备受争议，并且在几个系统中仍然鲜为人知，例如高度多样化的亚马逊盆地。我们确定了当地、集水区、空间和生物地理变量对河流鱼类的分类和功能 alpha 和 beta 多样性的相对作用。我们在亚马逊的六个河流流域中对 54 条溪流进行了采样。对于每条河流，我们获得了 35 个当地栖息地变量和 11 个气候集水区变量。水道距离和流域特征分别转换为空间和生物地理变量。我们发现分类阿尔法多样性对空间和局部预测因子都有反应，而其功能对应物主要与局部变量相关联。生物地理学是构建分类学和功能β多样性的主要因素，其次是集水区和局部变量。在当地，基质类型和隔离决定了物种和性状的数量和相对丰度。生物地理和环境变量之间的共同变化，尤其是海拔和坡度，与 β 多样性模式密切相关，表明栖息地过滤和扩散限制的共同作用。我们的结果表明，在大空间尺度的河流群落研究中需要包括空间和环境变量，因为它们与调节群落结构的不同过程有关。