Spatial heterogeneity in habitat quality and dispersal - individual decisions and their population dynamic consequences

随着种群变得更大，繁殖成功和存活率通常会下降，这是因为对食物或繁殖地等资源的竞争加剧。这一过程被称为密度依赖，几十年来一直是种群生态学的核心主题，尤其是因为它对于理解种群可能如何应对环境变化至关重要，例如栖息地丧失或气候变化。我们知道，密度依赖发生在广泛物种的种群中，但我们对涉及的过程知之甚少。这种缺乏理解的情况对受保护关注的物种尤为严重。因此，用来辅助种群保护决策的种群动力学模型往往缺乏密度依赖性，或者对所涉及的机制做出强有力的假设。当考虑个体在空间可变环境中的分散决策时，我们的知识缺乏尤其明显，尽管理论预测这些将在密度依赖中发挥关键作用。此外，越来越多的人认识到，对个人来说是明智的行为，因为他们留下了更多的后代，并不一定会带来可能的最好的群体水平的表现。因此，为了改善对种群过程的生态学理解，必须在个体扩散决定及其种群水平的后果之间建立联系。这种联系的一种运作方式是通过所谓的“缓冲效应”，即随着种群的增长，越来越多的个体被迫占据质量较差的栖息地，从而降低种群内个体的繁殖成功和生存。与这一观点一致的空间分布模式在脊椎动物中很普遍。然而，我们对这些模式背后的个体扩散决定，或者对人口增长或持久性的更广泛影响，知之甚少。在这个项目中，我们建议使用理论和经验相结合的方法来解决这些问题，后者基于关于脊椎动物种群(毛里求斯红隼)的最完整的长期数据集之一。我们的方法是新颖的，因为我们试图开发一个框架，使我们能够(1)解释个人在空间的扩散决定如何产生空间占用和密度依赖的模式，以及(2)探索在面临环境变化的情况下，扩散决定对人口增长和持久性的影响。因此，我们的研究将提供对扩散生态的一般见解，了解扩散如何产生空间分布模式和密度依赖，以及将扩散与种群动态联系起来的理论框架。

As a population gets larger breeding success and survival generally declines due to increased competition for resources such as food or breeding sites. This process is called density-dependence, and it has been a core theme in population ecology for decades, not least because it is pivotal to understanding how populations might respond to environmental change, such as habitat loss or changes in climate. We know that density-dependence occurs in populations across a wide range of species, but we have a rather limited idea of the processes involved. This lack of understanding is particularly acute for species of conservation concern. As a result, models of population dynamics used to aid decisions about their conservation often lack density-dependence, or make strong assumptions about the mechanisms involved. Our lack of knowledge is particularly pronounced when considering the dispersal decisions of individuals in spatially variable environments, even though theory predicts that these will play a key role in density-dependence. Also, it is increasingly recognized that behaviours that are sensible for individuals to adopt because they leave more offspring do not necessarily lead to best possible population-level performance. For improved ecological understanding of population processes, it is therefore essential to form a link between individual dispersal decisions and their population-level consequences. One way such links may operate is through the so-called 'buffer effect' in which an increasing proportion of individuals are forced to occupy poor quality habitat as a population grows, thereby driving down the breeding success and survival of individuals within the population. Spatial distribution patterns consistent with this idea are widespread in vertebrates. However, we have a limited idea about the individual dispersal decisions that underlie these patterns, or the wider implications for population growth or persistence. In this project, we propose to address these issues using a mix of theoretical and empirical approaches, the latter being based on one of the most complete long-term datasets available on a vertebrate population (the Mauritius kestrel). Our approach is novel in that we are attempting to develop a framework that allows us to (1) explain how individual dispersal decisions in space generate patterns of spatial occupancy and density-dependence, and (2) explore the consequences of dispersal decisions for population growth and persistence in the face of environmental change. As a result, our research will provide general insights into the ecology of dispersal, an understanding of how dispersal generates spatial distribution patterns and density-dependence, and a theoretical framework for linking dispersal to population dynamics.