White Easton R, Nagy John D, Gruber Samuel H
School of Life Sciences, Arizona State University, P,O, Box 874501, 85287 Tempe, USA.
Biol Direct. 2014 Nov 18;9(1):23. doi: 10.1186/1745-6150-9-23.
Long-lived marine megavertebrates (e.g. sharks, turtles, mammals, and seabirds) are inherently vulnerable to anthropogenic mortality. Although some mathematical models have been applied successfully to manage these animals, more detailed treatments are often needed to assess potential drivers of population dynamics. In particular, factors such as age-structure, density-dependent feedbacks on reproduction, and demographic stochasticity are important for understanding population trends, but are often difficult to assess. Lemon sharks (Negaprion brevirostris) have a pelagic adult phase that makes them logistically difficult to study. However, juveniles use coastal nursery areas where their densities can be high.
We use a stage-structured, Markov-chain stochastic model to describe lemon shark population dynamics from a 17-year longitudinal dataset at a coastal nursery area at Bimini, Bahamas. We found that the interaction between delayed breeding, density-dependence, and demographic stochasticity accounts for 33 to 49% of the variance in population size.
Demographic stochasticity contributed all random effects in this model, suggesting that the existence of unmodeled environmental factors may be driving the majority of interannual population fluctuations. In addition, we are able to use our model to estimate the natural mortality rate of older age classes of lemon sharks that are difficult to study. Further, we use our model to examine what effect the length of a time series plays on deciphering ecological patterns. We find that-even with a relatively long time series-our sampling still misses important rare events. Our approach can be used more broadly to infer population dynamics of other large vertebrates in which age structure and demographic stochasticity are important.
This article was reviewed by Yang Kuang, Christine Jacob, and Ollivier Hyrien.
长寿的海洋大型脊椎动物（如鲨鱼、海龟、哺乳动物和海鸟）天生易受人为死亡的影响。尽管一些数学模型已成功应用于管理这些动物，但通常需要更详细的处理方法来评估种群动态的潜在驱动因素。特别是，年龄结构、繁殖的密度依赖性反馈和人口统计学随机性等因素对于理解种群趋势很重要，但往往难以评估。柠檬鲨（Negaprion brevirostris）具有远洋成年阶段，这使得对它们进行研究在后勤上具有困难。然而，幼鲨使用沿海育幼区，那里它们的密度可能很高。
我们使用一个阶段结构的马尔可夫链随机模型，根据巴哈马群岛比米尼一个沿海育幼区的17年纵向数据集来描述柠檬鲨的种群动态。我们发现，延迟繁殖、密度依赖性和人口统计学随机性之间的相互作用占种群数量变化的33%至49%。
人口统计学随机性在该模型中贡献了所有随机效应，这表明未建模的环境因素的存在可能是导致大多数年度间种群波动的原因。此外，我们能够使用我们的模型来估计难以研究的老年柠檬鲨的自然死亡率。此外，我们使用我们的模型来研究时间序列的长度对解读生态模式有何影响。我们发现，即使有相对较长的时间序列，我们的抽样仍然遗漏了重要的罕见事件。我们的方法可以更广泛地用于推断年龄结构和人口统计学随机性很重要的其他大型脊椎动物的种群动态。
本文由杨匡、克里斯汀·雅各布和奥利维耶·希里安评审。
