Climate warming is predicted to alter routing and flows of energy through food webs due to the critical and varied effects of temperature on physiological rates, community structure, and trophic dynamics. Few studies, however, have experimentally assessed the net effect of warming on energy flux and food web dynamics in natural intact communities. Here, we test how warming affects energy flux and the trophic basis of production in a natural invertebrate food web by experimentally heating a stream reach in southwest Iceland by ~4°C for two years and comparing its response to an unheated reference stream. Previous results from this experiment showed that warming led to shifts in the structure of the invertebrate assemblage, with estimated increases in total metabolic demand but no change in annual secondary production. We hypothesized that elevated metabolic demand and invariant secondary production would combine to increase total consumption of organic matter in the food web, if diet composition did not change appreciably with warming. Dietary composition of primary consumers indeed varied little between streams and among years, with gut contents primarily consisting of diatoms (72.9%) and amorphous detritus (19.5%). Diatoms dominated the trophic basis of production of primary consumers in both study streams, contributing 79 - 86% to secondary production. Although warming increased the flux of filamentous algae within the food web, total resource consumption did not increase as predicted. The neutral net effect of warming on total energy flow through the food web was a result of taxon-level variation in responses to warming, a neutral effect on total invertebrate production, and strong trophic redundancy within the invertebrate assemblage. Thus, food webs characterized by a high degree of trophic redundancy may be more resistant to the effects of climate warming than those with more diverse and specialized consumers.

中文翻译：

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热生态位多样性和营养冗余驱动变暖对通过河流食物网的能量通量的中性影响

由于温度对生理速率、群落结构和营养动态的关键和不同影响，预计气候变暖将改变能量通过食物网的路径和流动。然而，很少有研究通过实验评估变暖对自然完整群落中能量通量和食物网动态的净影响。在这里，我们通过实验将冰岛西南部的一条河段加热约 4°C 两年，并将其响应与未加热的参考流进行比较，以测试变暖如何影响天然无脊椎动物食物网中的能量通量和生产的营养基础。该实验的先前结果表明，变暖导致无脊椎动物组合结构发生变化，估计总代谢需求增加，但年度二次生产没有变化。我们假设，如果饮食组成不随气候变暖而发生明显变化，那么代谢需求的增加和不变的二次生产将共同增加食物网中有机物的总消耗量。主要消费者的膳食成分确实在不同河流和年份之间几乎没有变化，肠道内容物主要由硅藻 (72.9%) 和无定形碎屑 (19.5%) 组成。在两个研究流中，硅藻在初级消费者生产的营养基础中占主导地位，对次级生产的贡献率为 79 - 86%。尽管变暖增加了食物网内丝状藻类的通量，但总资源消耗并没有像预测的那样增加。变暖对通过食物网的总能量流的中性净效应是对变暖反应的分类群水平变化的结果，对无脊椎动物总产量的中性影响，以及无脊椎动物组合内的强营养冗余。因此，以高度营养冗余为特征的食物网可能比拥有更多样化和专业化消费者的食物网更能抵抗气候变暖的影响。