Extreme drought pushes stream invertebrate communities over functional thresholds.
Extreme drought pushes stream invertebrate communities over functional thresholds.
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DOI：
10.1111/gcb.14495
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发表时间：
2019-01
影响因子：
11.6
通讯作者：
Ledger ME
中科院分区：
文献类型：
--
作者：
Aspin TWH;Khamis K;Matthews TJ;Milner AM;O'Callaghan MJ;Trimmer M;Woodward G;Ledger ME
功能特征越来越多地被用来预测长期气候变化情景下的物种灭绝风险和范围转移，但很少被用来研究对极端气候事件的脆弱性，如超季节干旱。在溪流中，干旱加剧可能超过栖息地丧失的门槛，在那里，环境条件的边际变化会引发不成比例的生物反应。然而，这些阈值仅从结构的角度进行了研究，函数非线性的存在仍然未知。我们探索了无脊椎动物群落功能特征沿着干旱强度梯度的趋势，模拟了18个月的时间，使用类似于低地源头溪流的中微体。我们根据干旱对性状过滤的先验预测对16个性状的反应进行了建模，并检验了通过系统聚类分析确定的性状分布组(TPG)的反应。由于干旱加剧的响应既是线性的，又是非线性的，选择广义加性模型(GAMS)来模拟响应曲线，并用拟合样条曲线的斜率来检测干旱期间的功能阈值。干旱在先验选择的性状中有12个(75%)引起了显著的反应。描述移动(分散、移动)和饮食的行为特征对中等强度的干旱很敏感，因为渠道被分割成孤立的池子。相比之下，在失去地表水之前，形态和生理特征表现出很小的反应，在这一点上，我们观察到体型、呼吸模式和耐热性的突然变化。不同的TPG的反应差异很大，从非空中分散者的种群崩溃，因为渠道支离破碎，到小型的温热饮食通才在极端脱水时的破坏。我们的研究首次证明，干旱强度的相对较小变化可以引发河流群落不成比例的大功能转移，这表明基于特征的方法可能特别有助于诊断对全球变化的灾难性生态反应。越来越多的研究正在利用物种的特征来诊断和预测它们对长期气候变化的反应，但很少有人探索物种特征对极端气候事件的敏感性，例如长期干旱。我们结合了大型操纵流动实验和基于特征的分析来阐明溪流大型无脊椎动物群落对加剧干旱的功能反应。干旱导致群落特征特征的突然和普遍的变化，并引发某些功能群体的种群崩溃，最明显的是那些由非飞行类群组成的群体。我们对多个响应阈值的检测表明，性状可能是物种和群落水平对极端干扰的抗性的有价值的功能生物标记。
Functional traits are increasingly being used to predict extinction risks and range shifts under long‐term climate change scenarios, but have rarely been used to study vulnerability to extreme climatic events, such as supraseasonal droughts. In streams, drought intensification can cross thresholds of habitat loss, where marginal changes in environmental conditions trigger disproportionate biotic responses. However, these thresholds have been studied only from a structural perspective, and the existence of functional nonlinearity remains unknown. We explored trends in invertebrate community functional traits along a gradient of drought intensity, simulated over 18 months, using mesocosms analogous to lowland headwater streams. We modelled the responses of 16 traits based on a priori predictions of trait filtering by drought, and also examined the responses of trait profile groups (TPGs) identified via hierarchical cluster analysis. As responses to drought intensification were both linear and nonlinear, generalized additive models (GAMs) were chosen to model response curves, with the slopes of fitted splines used to detect functional thresholds during drought. Drought triggered significant responses in 12 (75%) of the a priori‐selected traits. Behavioural traits describing movement (dispersal, locomotion) and diet were sensitive to moderate‐intensity drought, as channels fragmented into isolated pools. By comparison, morphological and physiological traits showed little response until surface water was lost, at which point we observed sudden shifts in body size, respiration mode and thermal tolerance. Responses varied widely among TPGs, ranging from population collapses of non‐aerial dispersers as channels fragmented to irruptions of small, eurythermic dietary generalists upon extreme dewatering. Our study demonstrates for the first time that relatively small changes in drought intensity can trigger disproportionately large functional shifts in stream communities, suggesting that traits‐based approaches could be particularly useful for diagnosing catastrophic ecological responses to global change. A growing number of studies are using species' traits to diagnose and predict their responses to long‐term climate change, but few have explored trait sensitivity to extreme climatic events, such as prolonged droughts. We combined a large manipulative flow experiment with traits‐based analyses to elucidate functional responses of stream macroinvertebrate communities to intensifying drought. Drought caused abrupt and pervasive changes in community trait profiles and triggered population collapses of certain functional groups, most notably those comprising non‐flying taxa. Our detection of multiple response thresholds indicates that traits could be valuable functional biomarkers for species‐ and community‐level resistance to extreme disturbance.
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