Linking species to ecosystems: predation-mediated nutrient flows

物种如何影响生态系统功能是生态学理论和应用研究的一个基本问题。越来越多的证据表明，大型食草动物对植物群落内的养分循环产生了强烈的影响。捕食者是否可以直接通过减少食草动物数量或间接通过改变食草动物行为来改变营养动态仍不清楚。我的研究解决了食草动物如何改变他们的行为，以避免捕食者在“恐惧的景观”，然后评估营养流的后果。利用阿尔伯塔中东部斜坡的实地研究数据，我检查了狼和麋鹿在时间和空间上分布之间的相关性，以测试麋鹿是否通过集中在狼不使用的区域（即，避难所），通过搬出狼经常光顾的地区（例如，贝壳游戏），或者通过避开狼的首选猎物所使用的栖息地（例如，分离）。然后，使用麋鹿扫描捕食者的直接观察（即，警惕）在开放的草原，我确定警惕摄入量的影响。从叮咬率和植物生物量之间的关系，我预测的“业余时间”的动物有多少可以扫描捕食者，并比较这与观察到的时间分配给警惕。接下来，我确定是否咬率下降，动物花更多的时间警惕，以及如何变化的同种觅食。最后，我评估麋鹿分布和喂养行为的变化是否会改变营养流，通过比较净碳和氮的回报（粪便和尿液减去饲料去除）在梯度的地区从低到高狼捕食风险。我的工作提供了一个机械的理解捕食的影响如何级联下降到较低的营养水平，通过营养流，目前还没有大型哺乳动物系统。

A fundamental issue of theoretical and applied research in ecology is how species affect ecosystem functioning. Evidence has accumulated that large-bodied herbivores exert a strong influence on nutrient cycling within plant communities. Whether predators can modify nutrient dynamics either directly by reducing herbivore numbers or indirectly by altering herbivore behaviour remains unclear. My research addresses how herbivores alter their behaviours to avoid predators in a "landscape of fear", and then evaluates consequences for nutrient flow. Using data from field studies in the central east slopes of Alberta, I examine correlations between the distributions of wolves and elk in both time and space to test whether elk avoid wolves by concentrating in areas not used by wolves (i.e., refuges), by moving out of areas when wolves frequent them (e.g., shell game), or by avoiding habitats used by the wolves' preferred prey (e.g., segregation). Then, using direct observations of elk scanning for predators (i.e., vigilance) in open grasslands, I determine the effect of vigilance on intake. From a relationship between bite rate and plant biomass I predict the amount of "spare time" animals have available to scan for predators, and compare this to the observed time allocated to vigilance. Next, I determine whether bite rate declines as animals spend more time vigilant and how this changes with the number of conspecific foragers. Finally, I assess whether changes in elk distribution and feeding behavior alter nutrient flows by comparing net carbon and nitrogen return (in feces and urine minus forage removed) across a gradient of areas from low to high wolf predation risk. My work provides a mechanistic understanding of how the influence of predation can cascade down to lower trophic levels through nutrient flows that is not currently available for large mammal systems.