Trait‐based approaches have broadened our understanding of how the composition of ecological communities responds to environmental drivers. This research has mainly focussed on abiotic factors and competition determining the community trait distribution, while effects of trophic interactions on trait dynamics, if considered at all, have been studied for two trophic levels at maximum. However, natural food webs are typically at least tritrophic. This enables indirect interactions of traits and biomasses among multiple trophic levels leading to underexplored effects on food web dynamics. Here, we demonstrate the occurrence of mutual trait adjustment among three trophic levels in a natural plankton food web (Lake Constance) and in a corresponding mathematical model. We found highly recurrent seasonal biomass and trait dynamics, where herbivorous zooplankton increased its size, and thus its ability to counter phytoplankton defense, before phytoplankton defense actually increased. This is contrary to predictions from bitrophic systems where counter‐defense of the consumer is a reaction to prey defense. In contrast, counter‐defense of carnivores by size adjustment followed the defense of herbivores as expected. By combining observations and model simulations, we show how the reversed trait dynamics at the two lower trophic levels result from a “trophic biomass–trait cascade” driven by the carnivores. Trait adjustment between two trophic levels can therefore be altered by biomass or trait changes of adjacent trophic levels. Hence, analyses of only pairwise trait adjustment can be misleading in natural food webs, while multitrophic trait‐based approaches capture indirect biomass–trait interactions among multiple trophic levels.

中文翻译：

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通过营养性浮游生物食物网级联的性状和生物量的耦合变化

基于特质的方法拓宽了我们对生态群落组成如何对环境驱动因素做出反应的理解。这项研究主要集中在非生物因素和决定群落性状分布的竞争上，而营养相互作用对性状动力学的影响（如果从根本上考虑）最多研究了两个营养水平。但是，天然食物网通常至少是营养的。这使得性状和生物量在多个营养水平之间间接相互作用，导致对食物网动态的探索不足。在这里，我们演示了在天然浮游生物食物网（博登湖）和相应数学模型中的三个营养级别之间相互性状调节的发生。我们发现季节性生物量和性状动态经常发生变化，在实际增加浮游植物防御能力之前，草食性浮游动物的体型增加了，从而抵抗了浮游植物防御能力。这与恶意系统的预测相反，即消费者的反防御是对猎物防御的反应。相比之下，通过调整大小来对食肉动物进行防御，则可以如预期的那样防御食草动物。通过将观察结果和模型模拟相结合，我们展示了在两个较低营养级别上逆向性状动态是如何由食肉动物驱动的“营养生物量-性状级联”产生的。因此，两个营养水平之间的性状调节可以通过相邻营养水平的生物量或性状变化来改变。因此，仅成对特征调整的分析可能会在天然食物网中产生误导，