Clements Christopher F, Ozgul Arpat
Department of Evolutionary Biology and Environmental Studies University of Zurich Zurich Switzerland.
Ecol Evol. 2016 Oct 5;6(21):7787-7793. doi: 10.1002/ece3.2531. eCollection 2016 Nov.
Critical transitions are qualitative changes of state that occur when a stochastic dynamical system is forced through a critical point. Many critical transitions are preceded by characteristic fluctuations that may serve as model-independent early warning signals, implying that these events may be predictable in applications ranging from physics to biology. In nonbiological systems, the strength of such early warning signals has been shown partly to be determined by the speed at which the transition occurs. It is currently unknown whether biological systems, which are inherently high dimensional and typically display low signal-to-noise ratios, also exhibit this property, which would have important implications for how ecosystems are managed, particularly where the forces exerted on a system are anthropogenic. We examine whether the rate of forcing can alter the strength of early warning signals in (1) a model exhibiting a fold bifurcation where a state shift is driven by the harvesting of individuals, and (2) a model exhibiting a transcritical bifurcation where a state shift is driven by increased grazing pressure. These models predict that the rate of forcing can alter the detectability of early warning signals regardless of the underlying bifurcation the system exhibits, but that this result may be more pronounced in fold bifurcations. These findings have important implications for the management of biological populations, particularly harvested systems such as fisheries, and suggest that knowing the class of bifurcations a system will manifest may help discriminate between true-positive and false-positive signals.
临界转变是随机动力系统在通过临界点时发生的状态质变。许多临界转变之前会出现特征性波动，这些波动可作为与模型无关的早期预警信号，这意味着这些事件在从物理学到生物学等各种应用中可能是可预测的。在非生物系统中，此类早期预警信号的强度已被证明部分取决于转变发生的速度。目前尚不清楚本质上高维且通常显示低信噪比的生物系统是否也具有这一特性，而这对于生态系统的管理方式具有重要意义，尤其是在对系统施加的力是人为的情况下。我们研究了强迫速率是否会改变（1）一个表现出折叠分岔的模型（其中状态转变由个体捕捞驱动）和（2）一个表现出跨临界分岔的模型（其中状态转变由放牧压力增加驱动）中的早期预警信号强度。这些模型预测，无论系统表现出何种潜在分岔，强迫速率都可以改变早期预警信号的可检测性，但这一结果在折叠分岔中可能更为明显。这些发现对生物种群的管理具有重要意义，尤其是对渔业等捕捞系统而言，并表明了解系统将表现出的分岔类别可能有助于区分真阳性和假阳性信号。
