Understanding the relative role of dispersal dynamics and niche constraints is not only a core task in community ecology, but also becomes an important prerequisite for bioassessment. Despite the recent progress in our knowledge of community assembly in space and time, patterns and processes underlying biotic communities in alpine glacierized catchments remain mostly ignored. To fill this knowledge gap, we combined the recently proposed dispersal-niche continuum index (DNCI) with traditional constrained ordinations and idealized patterns of species distributions to unravel community assembly mechanisms of different key groups of primary producers and consumers (i.e., phytoplankton, epiphytic algae, zooplankton, macroinvertebrates, and fishes) in rivers in the Qinghai-Tibet Plateau, the World's Third Pole. We tested whether organismal groups with contrasting body sizes differed in their assembly processes, and discussed their applicability in bioassessment in alpine zones. We found that community structure of alpine river biotas was always predominantly explained in terms of dispersal dynamics and historical biogeography. These patterns are most likely the result of differences in species-specific functional attributes, the stochastic colonization-extinction dynamics driven by multi-year glacier disturbances and the repeated hydrodynamic separation among alpine catchments after the rising of the Qilian mountains. Additionally, we found that the strength of dispersal dynamics and niche constraints was partially mediated by organismal body sizes, with dispersal processes being more influential for microscopic primary producers. Finding that zooplankton and macroinvertebrate communities followed clumped species replacement structures (i.e., Clementsian gradients) supports the notion that environmental filtering also contributes to the structure of high-altitude animal communities in glacierized catchments. In terms of the applied fields, we argue that freshwater bioassessment in glacierized catchments can benefit from incorporating the metacommunity perspective and applying novel approaches to (i) detect the optimal spatial scale for species sorting and (ii) identify and eliminate the species that are sensitive to dispersal-related processes.

中文翻译：

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历史和扩散过程驱动青藏高原冰川流域多种水生类群的群落聚集

了解扩散动态和生态位限制的相对作用不仅是群落生态学的核心任务，而且成为生物评估的重要前提。尽管我们对时空群落组装的了解最近取得了进展，但高山冰川流域生物群落的模式和过程仍然大多被忽视。为了填补这一知识空白，我们将最近提出的扩散生态位连续体指数（DNCI）与传统的约束排序和理想化的物种分布模式相结合，以揭示初级生产者和消费者的不同关键群体（即浮游植物、附生藻类）的群落组装机制。世界第三极青藏高原河流中的浮游动物、大型无脊椎动物和鱼类）。我们测试了具有对比体型的生物群体在组装过程中是否存在差异，并讨论了它们在高寒地区生物评估中的适用性。我们发现高山河流生物群的群落结构总是主要用扩散动力学和历史生物地理学来解释。这些模式很可能是物种特定功能属性差异、多年冰川扰动驱动的随机殖民-灭绝动态以及祁连山崛起后高山流域之间反复水动力分离的结果。此外，我们发现扩散动力学和生态位限制的强度部分是由生物体大小介导的，扩散过程对微观初级生产者的影响更大。浮游动物和大型无脊椎动物群落遵循聚集的物种替代结构（即克莱门氏梯度）的发现支持了这样的观点，即环境过滤也有助于冰川流域高海拔动物群落的结构。就应用领域而言，我们认为冰川流域的淡水生物评估可以受益于纳入元群落视角并应用新方法来（i）检测物种分类的最佳空间尺度和（ii）识别和消除敏感物种与分散相关的过程。