1. Dispersal, defined as the movement of individuals among local communities in a landscape, is a central regional determinant of metacommunity dynamics in ecosystems. Whereas both natural and anthropogenic ecosystem fragmentations can limit dispersal, previous attempts to measure such limitations have faced considerable context dependency, due to a combination of spatial extent and associated environmental variability, the wide range of dispersal modes, and abilities of organisms or variation in network topologies. Therefore, the role dispersal plays compared to local environmental filtering in explaining metacommunity dynamics remains unclear in fragmented dendritic ecosystems.
2. We quantified α‐ and β‐diversity components of invertebrate metacommunities across 10 fragmented headwater stream networks and tested the hypothesis that dispersal is the primary determinant of biodiversity organisation in these dynamic and spatially constrained ecosystems.
3. Alpha‐diversity was much lower in intermittent than perennial reaches, even long after rewetting, indicating an overwhelming effect of drying including a legacy effect on local communities.
4. Beta‐diversity was never correlated with environmental distances but predominantly explained by spatial distances accounting for river network fragmentation. The nestedness proportion of β‐diversity was considerable and reflected compositional differences where communities from intermittent reaches were subsets of perennial reaches.
5. Altogether, these results indicate dispersal as the primary process shaping metacommunity dynamics in these 10 headwater stream networks, where local communities recurrently undergo extinction and recolonisation events. This challenges previous conceptual views that local environment filtering is the main driver of headwater stream metacommunities.
6. As river networks become increasingly fragmented due to global change, our results suggest that some freshwater ecosystems currently driven by local environment filtering could gradually become dispersal‐limited. In this perspective, shifts from perennial to intermittent flow regimes represent ecological thresholds that should not be crossed to avoid jeopardising river biodiversity, functional integrity, and the ecosystem services they provide to society.

中文翻译：

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破碎促进了分散在确定10个间歇性源头河水上游群落中的作用

1. 散布定义为景观中当地社区之间个体的移动，是生态系统中元社区动态的中心区域决定因素。尽管自然和人为生态系统的碎片化都可能限制扩散，但由于空间范围和相关的环境可变性，广泛的扩散模式以及生物体的能力或网络变异的综合作用，先前测量此类限制的尝试都面临着相当大的背景依赖性。拓扑。因此，在零散的树突状生态系统中，与局部环境过滤相比，分散作用在解释元群落动态方面的作用尚不清楚。
2. 我们量化了10个零散的源头河网中无脊椎动物亚群落的α和β多样性成分，并检验了以下假设：在这些动态和空间受限的生态系统中，分散是生物多样性组织的主要决定因素。
3. 甚至在重新润湿后很长时间，间歇性的阿尔法多样性也要比多年生的低得多，这表明干燥的压倒性影响包括对当地社区的遗留影响。
4. Beta多样性从未与环境距离相关，而是主要由解释河流网络破碎化的空间距离来解释。β多样性的嵌套比例相当可观，反映了组成差异，其中间歇性河段的群落是多年生河段的子集。
5. 总而言之，这些结果表明，在这10个源头水流网络中，扩散是塑造元社区动态的主要过程，当地社区经常反复发生灭绝和重新定殖事件。这挑战了以前的概念观点，即局部环境过滤是源头上游水源群落的主要驱动力。
6. 随着由于全球变化而导致河网越来越支离破碎，我们的结果表明，当前由局部环境过滤驱动的一些淡水生态系统可能会逐渐受到扩散限制。从这个角度来看，从常年性流向间歇性流域的转变代表了生态阈值，不应越过该阈值，以免危害河流生物多样性，功能完整性及其为社会提供的生态系统服务。