REPRODUCTIVE STRATEGIES UNDER A CYCLIC ENVIRONMENT

了解野生动物种群是如何被调节或限制的，仍然是生态学中的一个突出问题，特别是在保护环境中。环境压力因素，如食物或其他资源的限制，决定了个体的出生率和死亡率，并最终使人口下降或恢复。人口生态学家一直在研究气候条件和人口密度之间的相互作用，作为资源限制的替代品。与模式物种的生活史反应可以联系到可预测的变化，在资源的可用性，在提高我们的能力，预测人口轨迹的研究发挥了重要作用。依赖于循环猎物物种的捕食者在这方面提供了一个有用的工具，因为它们通常会经历人口特征的显着变化，根据猎物密度的变化。此外，这种变化相对容易量化。在这里，我们提出了一个试点研究的黄褐色猫头鹰人口的基尔德森林，北方英格兰。这种夜间活动的猛禽是田鼠的专业捕食者。我们的目标是充分了解的后果，在猎物密度的变化在个人的生命周期。奇怪的是，这种分析很少在经历周期性人口变化的物种上进行，而最近估计，从螨到哺乳动物和鸟类，大约有三分之一的动物种群显示出这种周期性模式。生活在循环环境中的生物的生活史策略可能包括某些性状的表型可塑性，如第一次繁殖年龄或生殖投资，以使它们能够应对不断变化的猎物可用性。因此，可塑性有可能部分或完全缓冲猎物丰度变化的影响。首先，我们将考虑小猫头鹰出生时所经历的环境条件是否在其整个一生中都可以检测到。换句话说，我们将调查是否有一个“队列效应”猫头鹰生存，第一次繁殖的年龄，繁殖参数（如窝卵数或产卵日期）和繁殖频率。其次，我们将测量这些不同的生活史特征之间的协变，因为这种模式极大地影响了种群动态。第三，我们感兴趣的是确定是否表型不同的个体采取不同的生殖策略，以科普田鼠周期性，变异的来源，至少部分是可预测的时间。最后，该项目代表了全球理解在循环环境制度下如何调节种群的第一步。这样的知识出现在整个欧洲的啮齿动物物种的循环动力学目前消失的脸至关重要。这些物种确实是许多生态系统和食物链中的关键石种，许多掠食者，包括高度养护关切的物种，都直接和高度依赖它们。

Understanding how animal populations are regulated or limited in the wild still remains an outstanding issue in ecology, and especially in a conservation context. Environmental stressors such as limitations for food or other resources determine individual birth and death rates and ultimately make populations decline or recover. Population ecologists have been studying the interactions between climatic conditions and population density as surrogates for resource limitation. Studies with model species for which the life history response can be linked to predictable changes in resource availability serve an important role in improving our ability to predict population trajectories. Predators relying on cyclic prey species provide a useful tool in this context as they usually experience dramatic variation in demographic traits according to variation in prey densities. This variation is moreover relatively easy to quantify. Here we propose a pilot study on the tawny owl population of the Kielder Forest, northern England. This nocturnal raptor is specialist predator of field voles. Our objective is to fully understand the consequences of the variation in prey densities over individual lifetimes. Paradoxically, this analysis has only been seldom conducted on species experiencing cyclic demographic variation, while it has recently been estimated that about one third of animal populations, from mites to mammals and birds, display such cyclic patterns. Life history strategy of organisms living in cyclic environment may include phenotypic plasticity in some traits such as age of first reproduction or reproductive investment, so as to allow them to deal with changing prey availability. Plasticity thus has the potential to buffer partially or completely the impact of changes in prey abundance. First, we will consider whether environmental conditions experienced at birth by owlets remain detectable throughout their entire lifetime. In other words, we will investigate whether there is a 'cohort effect' on owl survival, age of first reproduction, breeding parameters (such as clutch size or laying date) and breeding frequency. Second, we will measure the covariation between these different life-history traits as this pattern greatly influences population dynamics. Third, we are interested in determining whether phenotypically different individuals adopt different reproductive strategies to cope with vole cyclicity, a source of variation that is at least partly predictable in time. Finally, this project represents an initial step toward the global understanding of how populations are regulated under cyclic environmental regime. Such knowledge appears critical in face of the current disappearance of cyclic dynamics in rodent species throughout Europe. Those species indeed constitute key stone species in many ecosystems and food chains, and numerous predators, including species of high conservation concern, are directly and highly dependent on them.