Data from: Drought intensification drives turnover of structure and function in stream invertebrate communities

Climatic extremes are becoming more frequent and intense across much of the globe, potentially transforming the biodiversity and functioning of affected ecosystems. In freshwaters, hydrological extremes such as drought can regulate beta diversity, acting as powerful environmental filters to dictate the complement of species and functional traits found at local and landscape scales. New methods that enable beta diversity and its functional equivalent to be partitioned into turnover (replacement of species/functions) and nestedness-resultant (gain/loss of species/functions) components may offer novel insights into the parallel impacts of drought on ecosystem structure and function. Using a series of artificial channels (mesocosms) designed to mimic perennial headwater streams, we experimentally manipulated streamflows to simulate a gradient of drought intensity. We then modelled taxonomic and functional turnover and nestedness of macroinvertebrate communities along this gradient, validating direct gradient approaches (bootstrapping, Mantel tests) against null models of nestedness. Drought intensification produced significant environmental distance decay trends (i.e. communities became increasingly taxonomically and functionally dissimilar the more differentially disturbed by drought they were). Taxonomic distance decay was primarily driven by turnover, while the functional trend reflected a combination of richness differences and turnover at different points along the gradient. Taxonomic and functional distance decay slopes were not significantly different, implying that communities were functionally vulnerable to drying. The increased frequency and intensity of droughts predicted under most climate change scenarios could thus profoundly modify not only the structure of running water invertebrate communities, but also the ecosystem functions they underpin.

全球多数区域的气候极端事件愈发频发且强度加剧，可能会改变受影响生态系统的生物多样性与生态系统功能。在淡水生态系统中，干旱这类水文极端事件可调控β多样性（beta diversity），作为强有力的环境过滤因子，决定局域及景观尺度下的物种与功能性状组合。能够将β多样性及其功能等价物拆解为更替（物种/功能的替代）与嵌套性成因（物种/功能的增减）组分的新方法，可为干旱对生态系统结构与功能的同步影响提供全新研究视角。本研究依托一系列旨在模拟常年性源头溪流的人工渠道（中型实验生态系统，mesocosms），通过实验调控溪流流量以构建干旱强度梯度。随后，我们针对该梯度下的大型无脊椎动物（macroinvertebrate）群落，构建了分类学更替、分类学嵌套性以及功能学更替、功能学嵌套性的分析模型，并以嵌套性零模型为参照，对直接梯度分析方法（自助法（bootstrapping）、曼特尔检验（Mantel tests））进行有效性验证。干旱加剧呈现出显著的环境距离衰减趋势：即群落受干旱干扰的差异越大，其分类学与功能学相似度越低。分类学距离衰减主要由物种更替驱动，而功能学距离衰减趋势则反映了梯度不同点位的物种丰富度差异与更替的共同作用。分类学与功能学距离衰减的斜率无显著差异，这意味着群落对溪流干涸存在功能层面的脆弱性。多数气候变化情景下预测的干旱事件频次与强度增加，不仅会深刻改变流水生无脊椎动物群落的结构，还会显著改变其支撑的生态系统功能。