Data from: Predator kairomones change food web structure and function, regardless of cues from consumed prey

Predation risk in aquatic systems is often assessed by prey through chemical cues, either those released by prey or by the predator itself. Many studies on predation risk focus on simple pairwise interactions, with only a few studies examining community-level and ecosystem responses to predation risk in species-rich food webs. Further, of these few community-level studies, most assume that prey primarily assess predation risk through chemical cues from consumed prey, even heterospecific prey, rather than just those released by the predator. Here, we compared the effects of different predation cues (predator presence with or without consumed prey) on the structure and functioning of a speciose aquatic food web housed in tropical bromeliads. We found that the mere presence of the top predator (a damselfly) had a strong cascading effect on the food web, propagating down to nutrient cycling. This predation risk cue had no effect on the identity of colonizing species, but strongly reduced the abundance and biomass of the macroinvertebrate colonists. As a result, bacterial biomass and nitrogen cycling doubled, with a concomitant decrease in bacterial production, but CO2 flux was unaffected. These community and ecosystem effects of predator presence cues were not amplified by the addition of chemical cues from consumed prey. Our results show that some of the consequences of predation risk observed in controlled experiments with simplified food webs may be observed in a natural, species-rich food web.水生系统中的捕食风险通常由猎物通过化学信号（chemical cues）进行评估，此类信号既可来自猎物自身，也可由捕食者本身释放。针对捕食风险的诸多研究多聚焦于简单的两两互作模式，仅有少数研究探讨了物种丰富型食物网内捕食风险对群落及生态系统的响应特征。此外，在上述为数不多的群落层面研究中，绝大多数研究均假设猎物主要通过被摄食猎物（乃至异种猎物）释放的化学信号评估捕食风险，而非仅依赖捕食者自身释放的信号。本研究对比了不同捕食信号（捕食者存在与否伴随被摄食猎物）对栖息于热带凤梨科植物（bromeliads）内的物种丰富型水生食物网的结构与功能的影响。研究发现，仅顶级捕食者（豆娘，damselfly）的存在就对食物网产生了显著的级联效应，其影响向下传递至养分循环过程。该捕食风险信号对定殖物种的类群组成无显著影响，但大幅降低了大型无脊椎动物（macroinvertebrate）定殖者的丰度与生物量。受此影响，细菌生物量与氮循环过程均翻倍，同时伴随细菌生产力的下降，但二氧化碳通量未受显著影响。捕食者存在信号所带来的上述群落与生态系统效应，并未因添加被摄食猎物释放的化学信号而得到进一步增强。本研究结果表明，此前在简化食物网控制实验中观测到的部分捕食风险效应，亦可在自然的物种丰富型食物网中得到印证。