Early warning signals of extinction in deteriorating environments
Early warning signals of extinction in deteriorating environments
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DOI：
10.1038/nature09389
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发表时间：
2010-09-23
期刊：
影响因子：
64.8
通讯作者：
Griffen, Blaine D.
中科院分区：
文献类型：
--
作者：
Drake, John M.;Griffen, Blaine D.
在走向灭绝的过程中，动物种群可能会呈现出强健种群所不具备的动态现象（1，2）。其中一些现象，如人口统计方差的缩放，与小尺寸有关（3-6），而另一些则是由密度依赖的非线性引起的（7）。虽然理解种群灭绝的原因几十年来一直是理论生物学的中心问题，但预测灭绝的能力仍然难以捉摸。在这里，我们认为，人口下降的原因是其灭绝的可预测性的核心。具体而言，环境退化可能导致种群动态出现一个临界点，对应于基本种群增长方程的一个分叉点，超过这个临界点，几乎可以肯定种群数量将下降至灭绝。在这种情况下，即将灭绝的信号将是临界减速（CSD）。我们进行了一项实验，重复实验室种群的大型蚤来验证这一假设。我们表明，人口跨越跨临界分岔，实验引起的控制下降的环境条件下，显示统计签名的CSD发病后的环境恶化和临界转变之前。在恒定环境中的种群没有这些模式。四个统计指标都显示，早在110天（类似于8代）之前的过渡发生的接近分叉的证据。两个综合指数提高了可预测性，比较分析表明，在没有参照人口标准化的情况下，仅仅根据对恶化环境的观察而发出的预警信号，由于恶化开始之前存在短暂的动态而受到阻碍，这表明在环境恶化开始之前必须有可靠的基线数据。种群动态模型中分叉的普遍性表明，这种现象应该是普遍的（10-12）。
During the decline to extinction, animal populations may present dynamical phenomena not exhibited by robust populations(1,2). Some of these phenomena, such as the scaling of demographic variance, are related to small size(3-6) whereas others result from density-dependent nonlinearities(7). Although understanding the causes of population extinction has been a central problem in theoretical biology for decades(8), the ability to anticipate extinction has remained elusive(9). Here we argue that the causes of a population's decline are central to the predictability of its extinction. Specifically, environmental degradation may cause a tipping point in population dynamics, corresponding to a bifurcation in the underlying population growth equations, beyond which decline to extinction is almost certain. In such cases, imminent extinction will be signalled by critical slowing down (CSD). We conducted an experiment with replicate laboratory populations of Daphnia magna to test this hypothesis. We show that populations crossing a transcritical bifurcation, experimentally induced by the controlled decline in environmental conditions, show statistical signatures of CSD after the onset of environmental deterioration and before the critical transition. Populations in constant environments did not have these patterns. Four statistical indicators all showed evidence of the approaching bifurcation as early as 110 days (similar to 8 generations) before the transition occurred. Two composite indices improved predictability, and comparative analysis showed that early warning signals based solely on observations in deteriorating environments without reference populations for standardization were hampered by the presence of transient dynamics before the onset of deterioration, pointing to the importance of reliable baseline data before environmental deterioration begins. The universality of bifurcations in models of population dynamics suggests that this phenomenon should be general(10-12).