Tail associations in ecological variables and their impact on extinction risk
Tail associations in ecological variables and their impact on extinction risk
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DOI：
10.1002/ecs2.3132
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发表时间：
2020-05-01
期刊：
影响因子：
2.7
通讯作者：
Reuman, Daniel C.
中科院分区：
文献类型：
--
作者：
Ghosh, Shyamolina;Sheppard, Lawrence W.;Reuman, Daniel C.
由于气候变化，极端气候事件（ECEs）变得越来越频繁和激烈。此外，有理由相信，环境变化可能会改变不同的人口生命率之间的“尾部关联”，或在不同地点测量的环境变量之间的值。两个变量之间的“尾部关联”是指变量分布左尾部或右尾部的值之间发生的关联。两个正相关的变量可以主要是“左尾相关的”（即，当它们取低值时比当它们取高值时更相关）或“右尾相关”（当它们取高值时比取低值时更相关），即使在两种情况下具有相同的总体相关系数。在非空间阶段结构矩阵模型的背景下，我们测试了特定阶段生命率之间的尾部关联是否会影响灭绝风险。我们还测试了环境变量的空间尾部关联的性质是否会影响集合种群灭绝风险。例如，如果一个环境变量的低值降低了当地种群的增长率，人们可能会认为左尾关联增加了集合种群灭绝的风险，因为环境“灾难”在空间上是同步的，可能会降低拯救效应的可能性。对于我们考虑的非空间、阶段结构模型，与右尾关联相比，生命率之间的左尾关联确实加重了灭绝风险，但影响很小。相比之下，我们发现，密度依赖与尾部关联相互作用，以影响集合种群灭绝风险大幅：人口模型显示补偿不足的密度依赖，左尾协会在环境变量往往强烈强调和右尾协会减轻灭绝风险，而相反的模型显示过度补偿密度依赖通常是正确的。在评估金融和其他领域的风险时，会考虑到尾部关联及其不对称性，但据我们所知，我们的研究是第一个考虑尾部关联如何影响种群灭绝风险的研究之一。我们的建模结果提供了一个新的机制影响灭绝风险的初步证明，在我们看来，应该有助于激励更全面的研究机制及其重要性的真实的人口在未来的工作。
Extreme climatic events (ECEs) are becoming more frequent and more intense due to climate change. Furthermore, there is reason to believe ECEs may modify "tail associations" between distinct population vital rates, or between values of an environmental variable measured in different locations. "Tail associations" between two variables are associations that occur between values in the left or right tails of the distributions of the variables. Two positively associated variables can be principally "left-tail associated" (i.e., more correlated when they take low values than when they take high values) or "right-tail associated" (more correlated when they take high than low values), even with the same overall correlation coefficient in both cases. We tested, in the context of non-spatial stage-structured matrix models, whether tail associations between stage-specific vital rates may influence extinction risk. We also tested whether the nature of spatial tail associations of environmental variables can influence metapopulation extinction risk. For instance, if low values of an environmental variable reduce the growth rates of local populations, one may expect that left-tail associations increase metapopulation extinction risks because then environmental "catastrophes" are spatially synchronized, presumably reducing the potential for rescue effects. For the non-spatial, stage-structured models we considered, left-tail associations between vital rates did accentuate extinction risk compared to right-tail associations, but the effect was small. In contrast, we showed that density dependence interacts with tail associations to influence metapopulation extinction risk substantially: For population models showing undercompensatory density dependence, left-tail associations in environmental variables often strongly accentuated and right-tail associations mitigated extinction risk, whereas the reverse was usually true for models showing overcompensatory density dependence. Tail associations and their asymmetries are taken into account in assessing risks in finance and other fields, but to our knowledge, our study is one of the first to consider how tail associations influence population extinction risk. Our modeling results provide an initial demonstration of a new mechanism influencing extinction risks and, in our view, should help motivate more comprehensive study of the mechanism and its importance for real populations in future work.