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.

全球多数区域的极端气候事件正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及其生态系统功能。在淡水生态系统中，干旱等水文极端事件可调控β多样性（beta diversity），通过强大的环境过滤作用决定局域及景观尺度下的物种组成与功能性状组合。能够将β多样性及其功能对应项拆解为周转（物种/功能替代）与嵌套成因（物种/功能增减）组分的新方法，可为干旱对生态系统结构与功能的协同影响提供全新视角。本研究依托一系列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模拟干旱强度梯度。随后，本研究沿该梯度对大型底栖无脊椎动物群落的分类学与功能周转及嵌套性进行建模，并以嵌套性零模型验证直接梯度分析方法（自举法，bootstrapping；曼特尔检验，Mantel tests）的有效性。干旱加剧呈现出显著的环境距离衰减趋势，即群落受干旱扰动的差异越大，其分类学与功能组成的相异性程度越高。分类学距离衰减主要由周转驱动，而功能距离衰减趋势则反映了梯度上不同点位的丰富度差异与周转的共同作用。分类学与功能距离衰减的斜率无显著差异，表明群落的功能组成对干旱化具有较高脆弱性。多数气候变化情景下预测的干旱事件频率与强度提升，不仅会深刻改变流水无脊椎动物群落的结构，还会显著影响其支撑的生态系统功能。