Data from: Piscivore addition causes a trophic cascade within and across ecosystem boundaries

The addition of predators can play a key role in structuring ecological communities through both consumptive and non-consumptive effects. Stocking of piscivorous fish in lakes and similar experimental introductions have provided fundamental evidence in support of trophic cascade theory. Yet, the impact of piscivore addition on cross ecosystem subsidies and meso-predator resource use has not been well studied. Here, we use a replicated pond experiment to document the trophic impacts of a piscivore, cutthroat trout Onchorhynchus clarkii, on aquatic communities already containing a meso-predatory fish (threespine stickleback Gasterosteus aculeatus) and neighbouring terrestrial ecosystems. We find that piscivore addition led to a trophic cascade that extended across an ecosystem boundary: trout addition increased the biomass and average size of insects emerging into the terrestrial system. Piscivores caused a diet shift in stickleback, a non-consumptive effect that was likely mainly responsible for the increase in emerging insect biomass. We additionally show that heterogeneity in the strength of the pelagic trophic cascade was more closely correlated with the magnitude of diet shift (reflecting a non-consumptive effect) than decreases in stickleback abundance (a consumptive effect). Taken together, our experiment demonstrates that the addition of a piscivore causes a trophic cascade that can extend beyond the aquatic system and suggests that non-consumptive effects may more strongly influence the strength of a trophic cascade than has been previously recognized.捕食者的引入可通过消耗性效应与非消耗性效应，在生态群落的结构构建中发挥关键作用。在湖泊中放养食鱼鱼类（piscivorous fish）及开展类似实验性引种，已为营养级联理论（trophic cascade theory）提供了基础性佐证。然而，食鱼鱼类添加对跨生态系统资源补贴以及中捕食者（meso-predator）资源利用的影响，尚未得到充分研究。本研究通过重复池塘实验，阐明了食鱼鱼类——割喉鳟（Onchorhynchus clarkii）对已包含中捕食性鱼类三棘刺鱼（Gasterosteus aculeatus）的水生群落，以及邻近陆地生态系统的营养级联影响。研究发现，食鱼鱼类的引入引发了跨越生态系统边界的营养级联效应：割喉鳟的投放提升了迁入陆地生态系统的昆虫生物量与平均个体体型。食鱼鱼类引发了三棘刺鱼的食性转变，这一非消耗性效应很可能是迁入昆虫生物量提升的主要驱动因素。此外，本研究还发现，浮游生境营养级联效应强度的异质性，与食性转变幅度（反映非消耗性效应）的相关性，显著高于与三棘刺鱼种群丰度下降（反映消耗性效应）的相关性。综合来看，本实验证实了食鱼鱼类的引入可引发跨越水生生态系统边界的营养级联效应，同时表明非消耗性效应对营养级联效应强度的影响，可能比此前认知的更为显著。