Sensitivity analysis code

This is the MatLab code corresponding to the sensitivity analysis of the publication \"Poaching of African elephants indirectly decreases population growth through lowered orphan survival\" by Parker et al., published in Current Biology in 2021. The summary for this publication is as follows: Prolonged maternal care is vital to the well-being of many long-lived mammals (Clutton-Brock, 1991). The premature loss of maternal care, i.e. orphaning, can reduce offspring survival even after weaning is complete (Watts et al., 2009; Foster et al., 2012; Andres et al., 2013; Stanton et al., 2020). However, ecologists have not explicitly assessed how orphaning impacts population growth. We examined the impact of orphaning on population growth in a free ranging African elephant population, using 19 years of individual-based demographic monitoring data. We compared orphan and nonorphan survival, performed a sensitivity analysis to understand how population growth responds to the probability of being orphaned and orphan survival, and investigated how sensitivity to these orphan parameters changed with level of poaching. Orphans were found to have lower survival compared to nonorphaned age mates, and population growth rate was negatively correlated with orphaning probability and positively correlated with orphan survival. This demonstrates that, in addition to its direct effects, adult elephant death indirectly decreases population growth through orphaning. Population growth rate’s sensitivity to orphan survival increased for the analysis parameterized using only data from years of more poaching, indicating orphan survival is more important for population growth as orphaning increases. We conclude that orphaning substantively decreases population growth for elephants and should not be overlooked when quantifying the impacts of poaching. Moreover, we conclude that population models characterizing systems with extensive parental care benefit from explicitly incorporating orphan stages, and encourage research into quantifying effects of orphaning in other social mammals of conservation concern.本数据集对应帕克（Parker）等人2021年发表于《当代生物学（Current Biology）》的论文《偷猎非洲象通过降低孤儿象存活率间接降低种群增长》的敏感性分析所用MATLAB（MatLab）代码。该论文的研究摘要如下：长期母育抚育对诸多长寿哺乳动物的生存健康至关重要（Clutton-Brock, 1991）。幼崽过早失去母育抚育，即沦为孤儿，即便在完成断乳后仍会降低后代存活率（Watts et al., 2009; Foster et al., 2012; Andres et al., 2013; Stanton et al., 2020）。但此前生态学界尚未明确评估幼崽沦为孤儿对种群增长的具体影响。本研究依托19年的个体水平种群监测数据，探究了野生非洲象种群中幼崽沦为孤儿对种群增长的影响：对比孤儿象与同龄非孤儿象的存活率，通过敏感性分析明确种群增长对沦为孤儿的概率及孤儿象存活率的响应规律，并考察了这些孤儿相关参数的敏感性随偷猎强度的变化趋势。研究结果显示，与同龄非孤儿象相比，孤儿象存活率更低；种群增长率与沦为孤儿的概率呈负相关，与孤儿象存活率呈正相关。这表明成年象死亡除直接影响种群动态外，还会通过引发幼崽沦为孤儿的途径间接降低种群增长。仅采用高偷猎年份数据进行参数化的分析中，种群增长率对孤儿象存活率的敏感性显著提升，这意味着随着沦为孤儿的概率升高，孤儿象存活率对种群增长的重要性也随之增强。本研究得出结论：幼崽沦为孤儿会实质性降低大象种群的增长速率，在量化偷猎的生态影响时，该因素不应被忽视。此外，针对存在广泛亲代抚育行为的物种构建种群模型时，明确纳入孤儿阶段将有助于提升模型性能，本研究呼吁开展相关研究，以量化沦为孤儿现象对其他具有保护价值的群居哺乳动物的影响。