Indirect effects of predator interactions and alternative prey in food webs

捕食者和猎物之间的相互作用强烈影响生态系统的功能，但捕食者对猎物的影响也受到与其他捕食者和猎物的相互作用的影响。这项拟议的研究将调查两个生态系统中的这种间接相互作用，这些生态系统的食物网络配置略有不同。两者都涉及捕食者和可供选择的猎物，但在一个系统中，一个猎物物种也会吃掉另一个猎物物种(即公会内的捕食)。浣熊和幽灵蟹是佛罗里达州高巢密度海滩上最重要的两种海龟巢穴捕食者。浣熊也吃幽灵蟹，降低了对海龟卵的捕食风险，但也利用它们的洞穴来定位巢，这增加了猎物的风险。通过控制幽灵蟹的密度并确定对卵存活的影响，我们将确定每个捕食者对海龟繁殖的直接影响和交互影响。由于加拿大三只受威胁的海龟在佛罗里达州筑巢，这项研究对加拿大具有保护意义。我们还将调查北极狐的猎物如何受到与替代猎物种群变化相关的捕食压力的影响。整个北极的旅鼠种群周期正在崩溃，而气候变化是最常被引用的解释。然而，鹅数量的指数增长可能有利于旅鼠捕食者，增加对旅鼠的捕食，并阻止它们从周期低点恢复。为了验证这一假设，我们将收集反映旅鼠种群趋势的柳树疤痕，这些伤疤反映了不同鹅群建立历史的地区，并比较了疤痕年龄频率下降率。我们还将研究其他对北极狐种群动态的影响，包括与猎物可获得性和饮食变化相关的应激反应和寄生虫负载。了解影响食物网间接相互作用的因素和涉及的机制对于预测未来物种丧失或环境扰动的影响很重要。

Interactions between predators and their prey strongly affect ecosystem function, but the impacts of predators on their prey are also affected by interactions with other predators and prey. The proposed research will investigate such indirect interactions in two ecosystems with slightly different food web configurations. Both involve predators with alternative prey, but in one system, one prey species also consumes another (i.e., intraguild predation). Raccoons and ghost crabs are the two most important sea turtle nest predators on high nest density beaches in Florida. Raccoons also consume ghost crabs, reducing predation risk to turtle eggs, but also use their burrows to locate nests, which enhances risk to prey. By manipulating ghost crab densities and determining the effects on egg survival we will determine the direct effect of each predator and interactive effects on turtle reproduction. As three of Canada's threatened marine turtles nest in Florida, this research has conservation implications for Canada. We will also investigate how prey of arctic fox are affected by changing predation pressure associated with population changes of alternative prey. Lemming population cycles are collapsing throughout the Arctic, and climate change is the most commonly invoked explanation. Yet the exponential increase in goose populations may benefit lemming predators, increasing predation on lemmings and preventing their recovery from cyclic lows. To test this hypothesis we will collect willow scars, which reflect lemming population trends, in areas with different histories of goose colony establishment and compare rates of scar-age frequency decline. We will also examine other influences on arctic fox population dynamics, including stress response and parasite loads related to changes in prey availability and diet. Understanding factors affecting indirect interactions in food webs and the mechanisms involved is important for predicting effects of future species loss or environmental perturbation.