Environmental heterogeneity and dispersal limitation are important drivers of beta diversity; however, their relative influence on the two fundamental components of beta diversity (i.e., species replacement and richness difference) has not been fully examined in montane streams. Here, we examined the relative importance of local environmental gradients and three physical distance matrices (i.e., overland, watercourse and cost distances) on beta diversity and its two components for a macroinvertebrate metacommunity in a stream network. To provide additional insights into community assembly, we also analysed variation in two deconstructed sub-communities based on dispersal ability (i.e., weak and strong dispersers). Both environmental filters and physical distances (dispersal limitation) drove patterns of overall beta diversity, with the former generally prevailing over the latter. Species replacement components showed stronger correlations with environmental gradients than physical distances, while the opposite is true for the richness difference components. Overland distances were generally more important than cost and watercourse distances for community dissimilarity of stream macroinvertebrates, implying that lateral dispersal out of stream corridors through flight was the major dispersal route in the studied steam network. As expected, community dissimilarity of strong dispersers was primarily shaped by environmental filtering, while community dissimilarity of weak dispersers was associated with the joint effects of environmental filtering and dispersal limitation. Our findings demonstrate that partitioning overall dissimilarity into species replacement and richness difference provides more insights into the processes driving spatial variability in biological communities compared with the utilization of total beta diversity alone. Our results support the notion that maintaining environmental heterogeneity and natural connectivity of stream networks should be effective measures to conserve regional biodiversity.

环境的异质性和扩散限制是β多样性的重要驱动力；但是，它们对β多样性的两个基本组成部分（即物种替代和丰富度差异）的相对影响尚未在山区河流中得到充分检验。在这里，我们研究了局部环境梯度和三个物理距离矩阵（即陆上，水道和成本距离）对贝塔多样性及其两个组成部分对河网中大型无脊椎动物亚群落的相对重要性。为了提供有关社区组装的更多见解，我们还基于分散能力（即弱分散者和强分散者）分析了两个解构子社区的变异。环境过滤器和物理距离（分散限制）都推动了总体Beta多样性的变化，前者通常胜过后者。物种替代成分与环境梯度的相关性要比物理距离强，而丰富度差异的成分则相反。陆上距离通常比成本和水道距离更重要，因为它们使河流大型无脊椎动物的群落不相似，这意味着通过飞行从河道走廊横向扩散是研究蒸汽网络的主要扩散途径。不出所料，强分散剂的社区差异主要由环境过滤决定，而弱分散剂的社区差异与环境过滤和分散限制的共同作用有关。我们的研究结果表明，与仅利用总β多样性相比，将总体不相似性划分为物种替代和丰富度差异可提供更多驱动生物群落空间变异性过程的见解。我们的结果支持这样一种观点，即保持环境异质性和河流网络的自然连通性应该是保护区域生物多样性的有效措施。