Black-swan events in animal populations
Black-swan events in animal populations
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DOI：
10.1073/pnas.1611525114
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发表时间：
2017-03-21
影响因子：
11.1
通讯作者：
Dulvy, Nicholas K.
中科院分区：
文献类型：
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作者：
Anderson, Sean C.;Branch, Trevor A.;Dulvy, Nicholas K.
黑天鹅是不太可能发生的事件，但往往会产生深远的影响。这些事件推动了社会系统的重要转变（例如，银行崩溃）和物理系统（例如，地震），但目前仍不清楚生态人口数量在多大程度上缓冲或遭受这种极端情况。在这里，我们估计的患病率和方向的黑天鹅事件（重尾过程噪声）在609动物种群占人口动态（生产力，密度依赖性，和典型的随机性）。我们在大约4%的人群中发现了黑天鹅事件的有力证据。这些事件最常发生在鸟类（7%），哺乳动物（5%）和昆虫（3%）中，并且不能用任何生活史协变量来解释，但往往是由外部扰动驱动的，如气候，严冬，捕食者，寄生虫或多种因素的综合影响。黑天鹅事件主要表现为种群死亡和崩溃（86%），而不是意外的增加，忽略重尾过程噪声导致低估了种群崩溃的幅度。我们建议建模者在预测种群丰度时考虑重尾向下倾斜的概率分布，例如这里使用的倾斜学生t。我们的研究结果表明，在人口建模重尾向下的事件，并制定保护策略，是强大的生态惊喜的重要性。
Black swans are improbable events that nonetheless occur-often with profound consequences. Such events drive important transitions in social systems (e.g., banking collapses) and physical systems (e.g., earthquakes), and yet it remains unclear the extent to which ecological population numbers buffer or suffer from such extremes. Here, we estimate the prevalence and direction of black-swan events (heavy-tailed process noise) in 609 animal populations after accounting for population dynamics (productivity, density dependence, and typical stochasticity). We find strong evidence for black-swan events in similar to 4% of populations. These events occur most frequently for birds (7%), mammals (5%), and insects (3%) and are not explained by any life-history covariates but tend to be driven by external perturbations such as climate, severe winters, predators, parasites, or the combined effect of multiple factors. Black-swan events manifest primarily as population die-offs and crashes (86%) rather than unexpected increases, and ignoring heavy-tailed process noise leads to an underestimate in the magnitude of population crashes. We suggest modelers consider heavy-tailed, downward-skewed probability distributions, such as the skewed Student t used here, when making forecasts of population abundance. Our results demonstrate the importance of both modeling heavy-tailed downward events in populations, and developing conservation strategies that are robust to ecological surprises.