自然种群中混沌的检测及其在种群动态研究中的意义

Detection of chaos in natural population and its significance in the study of population dynamics

混沌现象广泛地存在于自然界 ,2 0世纪 70年代以来 ,通过大量的生物模型模拟说明混沌也存在于生物系统中。几十年来生态学家一直在努力寻找混沌在自然生态系统存在的证据 ,但所获不多 ,这是源于自然的现实还是由于检测方法的不当和数据的局限 ?一直困扰着生态学家 ,自然界中对混沌的检测成为一个要点 ,也是一个难点。在概述混沌概念和性质的基础上 ,着重介绍目前在自然生态系统检测混沌的方法 ,对各种方法的应用条件和范围进行了概述。这些方法包括功率谱法、时间序列的自相关函数分析、模型参数估计、庞加莱截面法、全局和局域李雅普若夫特征指数的估计、吸引子关联维的确定、非线性预测。大量研究结果显示 ,虽然在自然界检测到的混沌的例子还不多 ,但其存在却是不容怀疑的。问题是什么样的系统在什么样的条件下会出现混沌 ?研究表明食物链的结构、种群的迁入和迁出、环境噪音都会对种群的复杂性动态特征产生影响。混沌动态可能对产生系统的多样性和适应性有利 ,它比随机系统对外界干扰的抵抗能力更强。自然界的变化和系统的维持是持续性和混沌相互矛盾统一的结果。害虫种群复杂性动态的研究为害虫的管理提供了更多的理论依据。混沌控制的理论和方法有可能为害虫管理提供新的思路和途径。在孤立的种群?

Chaos widely exist in nature and shows also exist in biological system by the it erations of biological models since 70's of 20 th century. For decades ecol ogists have been searching for evidences of existence of chaos in natural popula tions but got limited catches. This puzzled them. Is it the reality in nature or because of the bad data and method? The detection of chaos in natural populatio n is a significant and difficult issue. Based on the introduction of concept and theory of chaos, the methods of detecting chaos in natural population are summa rized in this paper. These include analysis of power spectrum, time series autoc orrelation function (ACF), estimate of model parameter, Poincaré section, estim ation of global and local Lyapunov exponents, measure of the dimension of the at tractor and nonlinear forecasting. Advantages, disadvantages and data requiremen ts of each method are discussed. Though there are limited examples of chaos in n atural population, its existence is undoubted. The more important questions are in what kind of system and in what condition the chaos comes up. From this point of view the estimation of local Lyapunov exponent is recommended which can be u sed to analyze this kind of questions. It has been proved that structure of food chain, immigration and emigration,environment noise can influence the pattern of complex population dynamics. Chaotic dynamics may contribute to generation of diversity and hence adaptability. Chaotic systems are also more robust than sto chastic ones for externally imposed perturbation. The sustainability and chaos a re combined together in nature so as to maintain the system and made it ongoing. The study of chaos and complex dynamics can provide guidance for the rational pest management. The theory and method of chaos control will lead to new pest co ntrol tactics and methods. In isolated populations chaos will increase the proba bility of extinction while in a meta-population situation the decorrelating eff ect of chaotic oscillations would reduce the degree of synchrony among local pop ulations and thus the likelihood that all are simultaneously extinguished. The r elationship between spatial structure and population extinction is an important aspect in conservation biology. More effort should be made in the study of compl ex and chaotic dynamics from population, community and ecosystem levels by means of remote sensing and GIS so as to understand more about how the chaos exist in nature and what is the role of it.