Herbivore physiological response to predation risk and implications for ecosystem nutrient dynamics
Herbivore physiological response to predation risk and implications for ecosystem nutrient dynamics
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DOI：
10.1073/pnas.1009300107
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发表时间：
2010-08-31
影响因子：
11.1
通讯作者：
Schmitz, Oswald J.
中科院分区：
文献类型：
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作者：
Hawlena, Dror;Schmitz, Oswald J.
营养物质在生态系统中的传递过程是生产、食物链长度和物种多样性的重要决定因素。一般观点认为，营养物质在食物链上传递的速率和效率受到食草动物为生存和生产获取富含氮化合物的特定能力的限制。然而，通过使用人工食物进行的饲养试验，我们发现蝗虫食草动物对蜘蛛捕食风险的生理应激反应改变了营养限制的性质。面临捕食风险的蝗虫比对照蝗虫具有更高的代谢率。相应地，代谢升高增加了对膳食可消化碳水化合物 - 碳的需求，以满足增加的能量需求。此外，可消化碳水化合物 - 碳在植物组织总碳含量中所占比例较小，因此植物与食草动物之间的营养传递相应地更多地受到可消化植物碳而非植物总碳氮比的限制。食草动物饮食的这种转变是为了满足改变后的营养需求，这增加了食草动物身体的碳氮比、蝗虫选择食物的植物群落的碳氮比以及蝗虫粪便的碳氮比。因此，长期的捕食风险改变了最终进入碎屑库并分解的动植物组织的质量。我们的研究结果表明，食草动物的生理机能使碳氮需求和营养摄入变得灵活，从而提供了一种机制来解释生态系统中营养物质传递的营养级控制性质的环境依赖性。
The process of nutrient transfer through an ecosystem is an important determinant of production, food-chain length, and species diversity. The general view is that the rate and efficiency of nutrient transfer up the food chain is constrained by herbivore-specific capacity to secure N-rich compounds for survival and production. Using feeding trials with artificial food, we show, however, that physiological stress-response of grasshopper herbivores to spider predation-risk alters the nature of the nutrient constraint. Grasshoppers facing predation risk had higher metabolic rates than control grasshoppers. Elevated metabolism accordingly increased requirements for dietary digestible carbohydrate-C to fuel-heightened energy demands. Moreover, digestible carbohydrate-C comprises a small fraction of total plant tissue-C content, so nutrient transfer between plants and herbivores accordingly becomes more constrained by digestible plant C than by total plant C:N. This shift in herbivore diet to meet the altered nutrient requirement increased herbivore body C:N content, the C:N content of the plant community from which grasshoppers select their diet, and grasshopper fecal C:N content. Chronic predation risk thus alters the quality of animal and plant tissue that eventually enters the detrital pool to become decomposed. Our results demonstrate that herbivore physiology causes C:N requirements and nutrient intake to become flexible, thereby providing a mechanism to explain context dependence in the nature of trophic control over nutrient transfer in ecosystems.