Indirect effects of predator interactions and alternative prey in food webs

捕食者与被捕食者之间的相互作用对生态系统的功能有着强烈的影响，但捕食者对被捕食者的影响也受到其他捕食者和被捕食者之间相互作用的影响。拟议的研究将调查这种间接相互作用在两个生态系统略有不同的食物网配置。两者都涉及捕食者和其他猎物，但在一个系统中，一个猎物物种也消耗另一个猎物物种（即，野生动物捕食）。浣熊和鬼蟹是佛罗里达州高巢密度海滩上最重要的两种海龟巢捕食者。浣熊也吃鬼蟹，减少了海龟蛋被捕食的风险，但也利用它们的洞穴定位巢穴，这增加了被捕食的风险。通过控制鬼蟹密度和确定对卵存活的影响，我们将确定每种捕食者的直接影响以及对海龟繁殖的交互影响。由于加拿大有三种濒危海龟在佛罗里达州筑巢，这项研究对加拿大的保护具有重要意义。我们还将研究北极狐的猎物如何受到与替代猎物数量变化相关的捕食压力变化的影响。整个北极地区的旅鼠种群周期正在崩溃，气候变化是最常用的解释。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，并阻止它们从周期性低点恢复。为了验证这一假设，我们将在不同鹅群建立历史的地区收集反映旅鼠种群趋势的柳树疤痕，并比较疤痕年龄频率下降的比率。我们还将研究对北极狐种群动态的其他影响，包括与猎物可用性和饮食变化相关的应激反应和寄生虫负荷。了解影响食物网中间接相互作用的因素及其机制对于预测未来物种损失或环境扰动的影响具有重要意义。

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.