Data from: Morphological drivers of trophic cascades

Worldwide, local anthropogenic extinctions have recently been reported to induce trophic cascades, defined as perturbations of top consumers that propagate along food chains down to primary producers. This focus on the effects of top-consumer extinction (i.e. of species presence) ignores potential cascading effects of the rapid morphological changes that may precede extinction. Here, we show in an experimental, three-level food chain including medaka fish, herbivorous zooplankton and unicellular algae that varying body length of a single fish from large (36.3 mm) to small (11.5 mm) induced a stronger trophic cascade than varying an average-sized (23.8 mm) fish from being present to absent. The strength of fish predation on zooplankton scaled quasi linearly (not with a power exponent) with fish body length and associated gape width, suggesting that the resultant trophic cascade was morphology (not metabolism)-dependent. The effect of fish body length was stronger on phyto- than on zooplankton, because large-sized fish had the unique ability to suppress large-sized herbivores, which in turn had high grazing capacities. Hence, our results show that consumer body size, by setting diet breadth, can both drive and magnify the strength of trophic cascades. In contrast, fish body shape had no significant effect on fish predatory performances when its allometric component (the effect of size on shape) was removed. In the wild, human-induced body downsizing of top consumers is widespread, and mitigating the resultant perturbations to ecosystem function and services will require a paradigm shift from preserving species presence towards preserving species size structure.全球范围内，近期有研究报道人为活动引发的局地物种灭绝可诱导营养级联效应（trophic cascade），后者被定义为顶级消费者的扰动沿食物链向下传递至初级生产者的过程。当前针对顶级消费者灭绝（即物种存续与否）所产生效应的研究视角，却忽略了灭绝前可能出现的快速形态变化所潜在的级联效应。本研究通过包含青鳉鱼（medaka fish）、植食性浮游动物以及单细胞藻类的三级食物链实验发现，将单条青鳉的体长从大型个体（36.3 mm）调整至小型个体（11.5 mm）所引发的营养级联效应，要强于将体长中等（23.8 mm）的青鳉从存在变为消失所产生的效应。青鳉对浮游动物的捕食强度与青鳉体长及相应口裂宽度呈准线性缩放关系（而非幂指数关系），这表明由此产生的营养级联效应取决于形态特征（而非代谢水平）。青鳉体长对浮游植物的调控效应强于对浮游动物的效应，这是因为大型青鳉可独有地抑制大型植食者，而这类大型植食者具备较高的摄食能力。因此，本研究结果表明，消费者体型可通过调控食谱宽度，同时驱动并放大营养级联效应的强度。与之相反，当去除异速生长成分（allometric component，即体型对形态的影响）后，青鳉的体型形状对其捕食性能并无显著影响。在自然环境中，人类活动导致的顶级消费者体型小型化现象普遍存在，若要缓解由此对生态系统功能与服务造成的扰动，亟需实现研究范式的转变——从仅保护物种存续，转向保护物种的体型结构。