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Environmental filtering and spatial processes have been associated with variation in ecological communities and biodiversity; however, their relative importance on multiple dimensions of beta diversity has not been fully explored in montane streams. Here, we examined the relative contribution of local, catchment and climate environmental variables and spatial factors to variation in three dimensions of macroinvertebrate beta diversity in the upper Han River Basin. Taxonomic, functional, and phylogenetic beta diversities and their respective turnover and nestedness components were calculated for macroinvertebrate assemblages sampled in a total of 130 stream sites across a large mountainous landscape. We investigated the correlations between beta diversity facets using MSR‐Mantel procedure and then examined the relative influence of each set of ecological factors through redundancy analysis and variance partitioning. Our results revealed relatively low spatial congruence among beta diversity dimensions, indicating these diversity dimensions are independent measures which offer complementary information of community assembly. Beta diversity dimensions and components were best explained by spatial and local environmental factors, whereas the large‐scale catchment and climate factors appeared less influential. Moreover, spatial and environmental factors generally exerted different controls on beta diversity depending on the dimensions under consideration. Taxonomic and phylogenetic beta diversities were more strongly determined by spatial factors via dispersal limitation, while functional beta diversity was mainly associated to local environments through habitat filtering. Our results challenge the perspective that using one diversity facet as a surrogate for others is enough, and highlight the need to integrate multiple diversity dimensions in metacommunity and biodiversity research. [ABSTRACT FROM AUTHOR]

Revealing the mechanisms underlying community organization has long been a central interest for ecologists and biogeographers. Recent findings have suggested that different dimensions of biodiversity may be shaped by contrasting ecological processes, offering complementary insights about community assembly. However, studies integrating multiple diversity facets across the Qinghai‐Tibetan Plateau (QTP) remain insufficient. We combined multiple analytical frameworks to unravel the patterns (taxonomic, functional and phylogenetic) and correlates (local environment, land use and dispersal pathways) of aquatic arthropod diversity in lotic (stream) and lentic (wetland) ecosystems of the QTP. We observed strong phylogenetic signals in most functional traits, pointing to the influence of evolutionary processes on these faunas. Null models indicated that community structure in most streams and wetlands was mostly the result of random draws from the regional functional and phylogenetic species pool. The prevalence of stochasticity was most likely associated with the interplay of the paleogeographical history, the extremely harsh environmental conditions at high elevations and the subsequent impoverishment of the regional species pool. However, some streams and wetlands also exhibited phylogenetic overdispersion and functional clustering, emphasizing the potential importance of competitive exclusion and habitat filtering, respectively. Variation partitioning further revealed that both environmental filtering and dispersal limitation accounted for the spatial variation of diversity measures, with local environment overriding the effects of space and catchment land use. Overall, this study improves our understanding of community organization and diversity patterns in environmentally extreme alpine catchments, with broad implications for the conservation and management of one of the world’s most important high‐altitude treasures. [ABSTRACT FROM AUTHOR]