Population dynamics of resource limited predators: Individuals differences and condition dependent dispersal

当地人口是由受到各种环境条件影响的个体组成的，这些环境条件影响了它们的生活史、决定、随后的分散模式和生殖表现。这些决定在年度队列内部和跨年度队列中产生个体质量的异质性，以及代际效应，例如母亲效应。迄今为止，在种群动态预测模型中对这些异质性来源的考虑仅限于生殖特征，并且主要基于居住在封闭系统（主要是岛屿）的种群，没有或有限的分散。然而，分散不仅是一个有影响力的人口特征，而且它也越来越被认为是理解人口如何应对环境变化的关键。在这个项目中，我们将研究个体质量的变化及其在种群动态中的作用，同时考虑其对繁殖和扩散性状的影响。我们将通过一项独特的、大型的、长期的研究来实现这一目标，该研究专门设计用于检测多尺度的分散，并以循环田鼠种群（茶色猫头鹰的主要猎物）的时空动态的显著变化为特征，从而研究生活史特征（包括分散）对异步捕食者种群总体动态的潜在贡献。在所有重要的人口特征中，估计分散可能是最大的困难：在人口相关的空间尺度上获得对其频率的无偏估计是具有挑战性的。这个项目之所以成为可能，要归功于一个独特的广泛而非常详细的数据集，包括茶色猫头鹰的丰度和生活史特征，以及佩蒂和合作者自1980年以来在英格兰北部基尔德森林600平方公里范围内连续收集的猎物丰度的详细测量。自1979年以来，每年都在大片区域（175平方公里）测量茶色猫头鹰的繁殖，大多数猫头鹰在巢箱中繁殖。定期检查巢箱可以提供领地占用、窝卵数量和蛋量、孵化顺序、羽翼成功的数据，以及允许计算条件指数的生物识别技术。此外，在整个研究期间，平均捕获了84%的繁殖雌性，在11年期间捕获了78%的繁殖雄性。总体而言，捕获-标记-再捕获（CMR）数据包括2000多只雏鸟和170多只成年鸟，在1981年至2005年期间，仅在基尔德森林就积累了大约1000次再捕获事件，在研究区域及以外地区发现了156多只死亡。为了本研究的独特目的，密集的Kielder森林研究区域由3个卫星区域（Wark， Kershope和Redesdale森林）补充，其中很大一部分雏鸡也是环状的。这些数据非常适合最近开发的捕获-再捕获建模技术，允许同时对来自各种动物遭遇的信息进行建模，从而产生最大的统计能力。特别是，将再捕获数据与死亡恢复数据相结合是估计扩散模式的有力工具。同时，在经验数据的指导下，我们将阐明扩散行为与由此产生的密度依赖之间的关系，这是种群同步的关键决定因素。所研究的系统在猎物动态方面经历了显著的季节性变化，即时空自相关性的丧失，与气候变化相一致。因此，它作为一个罕见的模型系统，用于研究捕食者对观察到的和预期的环境变化的反应。

Local populations are composed of individuals that have been subject to varying environmental conditions influencing their life history decisions, subsequent dispersal patterns and reproductive performance. These decisions generate heterogeneity in individual quality within and across annual cohorts as well as intergenerational effects, such as maternal effects. To date, consideration of these sources of heterogeneity in predictive models of population dynamics have been restricted to reproductive traits, and been based mostly on populations inhabiting enclosed systems, mainly islands, with no or limited dispersal. Yet, not only is dispersal an influential demographic trait but it is also increasingly recognised as key to understanding how populations respond to environmental change. In this project, we will investigate variation in individual quality and its role in population dynamics by simultaneously considering its influence on reproductive and dispersal traits. We will achieve this using a unique, large, long-term study of ringed Tawny owls specifically designed to detect dispersal at multiple scales and characterised by marked changes in the spatio-temporal dynamics of cyclic field vole populations, the main prey of tawny owls, and hence in the potential contribution of life history traits including dispersal to the overall dynamics of asynchronous predator populations. Of all the important demographic traits, estimating dispersal poses perhaps the biggest difficulties: obtaining unbiased estimates of its frequency at demographically relevant spatial scales is challenging. This project is made possible thanks to a uniquely extensive and very detailed data set of tawny owl Strix aluco, abundance and life history traits, together with detailed measures of prey abundance collected continuously by Petty and collaborators since 1980 over 600 km2 in Kielder Forest, in northern England. Reproduction of tawny owls has been measured annually since 1979 in a large area (175 km2) where most owls breed in nest-boxes. Regular nest-box checks provide data on territory occupancy, clutch size and egg volume, hatching order, fledgling success, as well as biometrics allowing the calculation of condition index. In addition, adult breeders were caught with an average 84% of the breeding females over the whole study period and 78% of breeding males over an 11-yr period. Overall, Capture-Mark-Recapture (CMR) data consist in more than 2000 individuals banded as chicks and more than 170 banded as adults, cumulating ca. 1000 recapture events between 1981 and 2005 in Kielder Forest alone, and more than 156 dead recoveries in the study area and beyond. Uniquely for the purpose of this study, the intensive Kielder Forest study area is supplemented by 3 satellite areas (Wark, Kershope and Redesdale forests) where a large fraction of chicks are also ringed. These data are highly suited to recently developed capture-recapture modelling techniques allowing simultaneous modelling of information from a variety of animal encounters so as to yield maximum statistical power. In particular, combining recapture data with dead recoveries is a powerful tool for the estimation of dispersal pattern Simultaneously, and guided by empirical data, we will clarify the relationship between dispersal behaviour and the resulting density dependence in dispersal, a key determinant of population synchrony. The system under study has experienced marked, season-specific changes in prey dynamics, namely loss in spatial and temporal autocorrelations, coincident with climate change. As such, it serves as a rare model system for investigating the response of a predator to observed and expected environmental change.