Linking the energetics of reproduction to population demography in a marine apex predator

人口的变化是由于出生率、死亡率和（或）移民率的变化。要更好地估计人口增长率，就必须更深入地了解影响这些重要增长率的潜在机制过程。这反过来又可以对环境变化对人口可能产生的影响进行先验评估。我们提出了这样一种自下而上的方法来理解环境变化、哺乳能量学以及随后在海洋顶级捕食者加拉帕戈斯海狮（Zalophus wollebaeki）种群中幼崽存活率和雌性繁殖力的变化之间的联系。基于我们从2003年开始进行的长期、基于个体的研究，我们建议通过双标记水法结合一岁仔的稳定同位素分析来测量哺乳的能量学。这将使我们了解一岁幼仔觅食行为的变化与哺乳行为的变化之间的关系。在母体方面，我们将能够估计哺乳的能量成本以及这与生育计划的协变。这将为我们提供一个非常详细的见解，如何变化的生命率产生的近似过程。我们将在年龄结构矩阵模型中纳入生命率的这种变化，其中生命率条目是环境变化的函数。在随后的第二个模型步骤中，我们将纳入强大的队列效应，并检验人口稳定主要是由于一些队列的生存和繁殖比平均水平好得多的假设，因此这些平均生命率估计并没有捕捉到推动人口增长的过程。因此，我们对海狮的长期研究处于一个独特的位置，可以将近因和终极因素结合起来，因为种群数据和大的环境扰动使我们能够深入了解驱动过程。

Changes in a population are due to changes in birth, death and/or immigration rates. A deeper understanding of the underlying mechanistic processes affecting these vital rates is essential for better estimation of population growth rates. This in turn, will allow the a priori assessment of the likely impact of environmental change on populations. We propose such a bottom-up approach to understand the linkage between environmental variation, the energetics of lactation and subsequent variation in juvenile survival and female fertility in a population of a marine apex predator, the Galapagos sea lion (Zalophus wollebaeki). Building on our long-term, individual-based study that has been running since 2003, we propose to measure the energetics of lactation by the doubly-labelled water method in combination with stable isotope analyses of yearlings. This will allow us to understand how variation in foraging behaviour of yearlings relates to variation in suckling behaviour. On the maternal side, we will be able to estimate the energetic cost of lactation and how this covaries with fertility schedules. This will provide us with an unusually detailed insight into how variation in vital rates arises from proximate processes. We will incorporate this variation in vital rates in age-structured matrix models where vital rate entries are functions of environmental variation. In a subsequent second model step, we will incorporate strong cohort effects and test the hypothesis that population stability is mainly due to some cohorts surviving and reproducing much better than average and that these average vital rate estimates do hence not capture the processes driving population growth. Our long-term sea lion study is hence in a unique position to combine proximate and ultimate factors because the population data and the large environmental perturbations allow us to gain a deep insight into the driving processes.