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

随着种群规模的扩大，由于对食物或繁殖地点等资源的竞争加剧，繁殖成功率和存活率通常会下降。这个过程被称为密度依赖，几十年来一直是人口生态学的核心主题，尤其是因为它对于理解人口如何应对环境变化（如栖息地丧失或气候变化）至关重要。我们知道，密度依赖性在很多物种的种群中都存在，但我们对其中的过程却知之甚少。对于需要保护的物种来说，这种缺乏理解的情况尤其严重。因此，用于帮助做出保护决策的种群动态模型往往缺乏密度依赖性，或者对相关机制做出强有力的假设。当考虑到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，人们越来越认识到，对个人来说明智的行为，因为它们留下了更多的后代，并不一定会导致最好的可能的种群水平的表现。因此，为了提高对种群过程的生态理解，必须在个体的分散决定与其种群水平的后果之间建立联系。这种联系的一种方式可能是通过所谓的“缓冲效应”，随着人口的增长，越来越多的个体被迫占据质量较差的栖息地，从而降低了种群中个体的繁殖成功率和存活率。与这一观点相一致的空间分布模式在脊椎动物中广泛存在。然而，我们对这些模式背后的个体分散决定，或对人口增长或持久性的更广泛影响的认识有限。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，后者是基于一个最完整的脊椎动物种群（毛里求斯红隼）的长期数据集。我们的方法是新颖的，因为我们正试图建立一个框架，使我们能够(1)解释空间中的个体分散决策如何产生空间占用和密度依赖模式，以及(2)探索面对环境变化时分散决策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学的一般见解，了解扩散如何产生空间分布模式和密度依赖性，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.