Dalton Christopher M, Flecker Alexander S
Department of Ecology and Evolutionary Biology, Cornell University, Corson Hall, 215 Tower Road, Ithaca, NY, 14853, USA,
Oecologia. 2014 Nov;176(3):691-701. doi: 10.1007/s00442-014-3084-6. Epub 2014 Sep 26.
Consumer-driven nutrient recycling, the release of chemicals as byproducts and excesses of consumer physiology, can alter ecosystems by changing the availability of limiting nutrients at the base of the food web. The mere presence of predators can alter consumer physiology by restricting food intake and inducing stress. Predation risk, then, can influence ecosystem function by modifying the role of prey as nutrient recyclers, yet there are few empirical tests of how predation risk alters nutrient recycling by prey. Here, we present the results of a test for the effects of predation risk on the C and N budgets of Trinidadian guppies (Poecilia reticulata). We reared female guppies for 7 weeks on diets of varying quality, and we compared control individuals to those exposed continuously to chemical cues emitted by a guppy predator, Crenicichla alta. We measured food consumption, growth rate, tissue elemental stoichiometry and N excretion by guppies on all treatments. Guppies strongly reduced food intake in the presence of predator cues; however, cue-exposed guppies assimilated nutrients more efficiently than controls. Specifically, cue-exposed guppies strongly increased N retention efficiency while only moderately increasing C efficiency. Consequently, guppies reared with predator cues excreted 39% less N than control guppies. We suggest that reduced foraging, enhanced nutrient efficiency, and decreased N excretion are adaptive responses to the extrinsic mortality threat posed by guppy predators. The resulting substantial reduction in N excretion by guppies may influence ecosystem function in natural streams by reducing the supply of a limiting nutrient.
消费者驱动的养分循环，即作为消费者生理过程副产品和过剩物释放的化学物质，可通过改变食物网底部限制性养分的可利用性来改变生态系统。捕食者的存在本身就可以通过限制食物摄入和引发应激来改变消费者的生理状态。因此，捕食风险可以通过改变猎物作为养分循环者的作用来影响生态系统功能，然而，关于捕食风险如何改变猎物的养分循环，几乎没有实证检验。在这里，我们展示了一项关于捕食风险对特立尼达孔雀鱼（Poecilia reticulata）碳和氮预算影响的测试结果。我们用不同质量的食物饲养雌性孔雀鱼7周，并将对照个体与持续暴露于孔雀鱼捕食者高氏丽鱼（Crenicichla alta）发出的化学信号中的个体进行比较。我们测量了所有处理组中孔雀鱼的食物消耗量、生长速率、组织元素化学计量和氮排泄量。在有捕食者信号的情况下，孔雀鱼会大幅减少食物摄入量；然而，暴露于信号中的孔雀鱼比对照组更有效地吸收养分。具体而言，暴露于信号中的孔雀鱼显著提高了氮保留效率，而碳效率仅适度提高。因此，在有捕食者信号环境下饲养的孔雀鱼氮排泄量比对照孔雀鱼少39%。我们认为，觅食减少、养分效率提高和氮排泄减少是对孔雀鱼捕食者带来的外在死亡威胁的适应性反应。孔雀鱼氮排泄量的大幅减少可能会通过减少一种限制性养分的供应来影响天然溪流中的生态系统功能。
