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。更深入地了解影响这些生命增长率的潜在机制过程，对于更好地估计人口增长率至关重要。反过来，这将允许对环境变化对人口的可能影响进行先验评估。我们提出了这样一种自下而上的方法来理解环境变化、哺乳能量以及随后在海洋顶端捕食者加拉帕戈斯海狮(Zalophus Wollebaeki)种群中幼体存活率和雌性生育力的变化之间的联系。基于我们自2003年开始的长期、基于个体的研究，我们建议用双标记水法结合一周岁婴儿的稳定同位素分析来测量哺乳期的能量。这将使我们了解一岁幼崽觅食行为的变化与哺乳行为的变化之间的关系。在母亲方面，我们将能够估计哺乳的能量成本，以及这如何与生育时间表相关。这将为我们提供一个异常详细的洞察力，了解生命频率的变化是如何从近过程中产生的。我们将把这种生命速率的变化纳入年龄结构矩阵模型中，在该模型中生命速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，并测试这样的假设，即人口稳定主要是由于一些队列的存活和繁殖远远好于平均水平，因此这些平均生死率估计没有捕捉到推动人口增长的过程。因此，我们的长期海狮研究处于一个独特的位置，可以结合最近和最终的因素，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.