Department of Ecology and Genetics; Limnology, Uppsala University, Uppsala, Sweden.
J Anim Ecol. 2021 Apr;90(4):834-845. doi: 10.1111/1365-2656.13413. Epub 2021 Jan 11.
According to apparent competition theory, sharing a predator should cause indirect interactions among prey that can affect the structure and the dynamics of natural communities. Though shifts in prey dominance and predator resource use along environmental gradients are rather common, empirical evidence on the role of indirect prey-prey interactions through shared predation particularly with increasing productivity, is still scarce. In an 8-week lake mesocosm experiment, we manipulated both the addition of inorganic nutrients and the presence of generalist fish predators (crucian carp, Carassius carassius L.), to test for the effects of indirect interactions through shared predation along a productivity gradient. We found that apparent mutualism (indirect positive interaction) between benthic and pelagic prey strongly affected short-term responses of aquatic food webs to increasing productivity in the presence of a generalist fish. Increasing productivity favoured the relative abundance of benthic prey, following trends in natural productive lake systems. This led to a shift in fish selectivity from pelagic to benthic prey driven by changes in fish behaviour, which resulted in apparent mutualism due to the lower and delayed top-down control of pelagic prey at increasing productivity. Our results show empirical evidence that the coupling of multiple production pathways can lead to strong indirect interactions through shared predation, whereby prey dynamics on short time-scales are highly dependent on the foraging behaviour of generalist predators. This mechanism may play an important role in short-term responses of food webs across environmental gradients.
根据明显竞争理论，分享捕食者应该会导致猎物之间产生间接相互作用，从而影响自然群落的结构和动态。尽管沿着环境梯度猎物优势和捕食者资源利用的转变相当普遍，但关于通过共享捕食产生的间接猎物-猎物相互作用的实证证据，特别是在生产力增加的情况下，仍然很少。在为期 8 周的湖泊中观实验中，我们同时操纵了无机养分的添加和一般鱼类捕食者（鲫鱼，Carassius carassius L.）的存在，以检验随着生产力的增加，通过共享捕食产生的间接相互作用的作用。我们发现，底栖和浮游猎物之间的明显共生关系（间接的正相互作用）强烈影响了一般鱼类存在时水生食物网对生产力增加的短期反应。随着生产力的增加，底栖猎物的相对丰度增加，这符合自然富营养湖泊系统的趋势。这导致鱼类选择性从浮游生物转向底栖猎物，这是由鱼类行为变化驱动的，这导致由于浮游生物猎物在生产力增加时的自上而下控制较低且延迟，从而出现明显的共生关系。我们的研究结果提供了经验证据，表明多种生产途径的耦合可能会导致通过共享捕食产生强烈的间接相互作用，从而导致短时间尺度上猎物动态高度依赖于一般捕食者的觅食行为。这种机制可能在环境梯度上的食物网短期反应中发挥重要作用。
