种群统计随机性和环境随机性对种群绝灭的影响

影响种群绝灭的随机干扰可分为种群统计随机性、环境随机性和随机灾害三大类。在相对稳定的环境条件下和相对较短的时间内，以前两类随机干扰对种群绝灭的影响为生态学家关注的焦点。但是，由于自然种群动态及其影响因子的复杂特征，进一步深入研究随机干扰对种群绝灭的作用在理论上和实践上都必须发展新的技术手段。本文回顾了种群统计随机性与环境随机性的概念起源与发展，系统阐述了其分析方法。归纳了两类随机性在种群绝灭研究中的应用范围、作用方式和特点的异同和区别方法。各类随机作用与种群动态之间关系的理论研究与对种群绝灭机理的实践研究紧密相关。根据理论模型模拟和自然种群实际分析两方面的研究现状，作者提出了进一步深入研究随机作用与种群非线性动态方法的策略。指出了随机干扰影响种群绝灭过程的研究的方向：更多的研究将从单纯的定性分析随机干扰对种群动力学简单性质的作用，转向结合特定的种群非线性动态特征和各类随机力作用特点具体分析绝灭极端动态的成因，以期做出精确的预测。

The affecting of demographic stochasticity and environmental stochasticity to population extinction

Understanding the risk of extinction affecting single populations is important in both theoretical and applied ecology. The interplay between noise and population dynamics is considerable importance especially for threatened species. We review the origin and developments of the demographic stochasticity and environmental stochasticity notions, it is relating closely with the study on population extinction mechanisms. Different stochastic factors affecting population extinction can be distinguished from three ways: its affecting characters, for demographic stochasticity rises a continuous affect to population and environmental stochasticity rises nearly continuous or sudden affects to population; its affecting population characters, for demographic stochasticity is most important in small populations and environmental stochasticity is important in both large and small populations; and its affecting intension, for environmental stochasticity arises usually series of larger perturbations to populations than demographic stochasticity. Stochastic factors affecting the demography of a single population are analyzed to determine the relative risks of extinction from demographic stochasticity and environmental stochasticity with the mean time to extinction of populations in an environment with constant carrying capacity but under stochastic demography or/and external noise. We point out that different model forms will cause different results on the population dynamics in noise. We also explain that whether maximization of intrinsic growth rate decreases the risk of extinction or not depends strongly on the population regulation mechanism. There are complex interplays between stochasticity and population dynamics. We discuss the important of demographic stochasticity for small population extinctions in different conditions by stochastic birth and death process with the variability of intrinsic rate, and environmental stochasticity for single population in different models from simple to complex form. Random variations in organisms' environments may affect their life-histories and therefore their population dynamics. Then, quantitatively accurate prediction of population extinction requires consideration of environmental variation and its impact. We predict that the study of the interplay between stochasticity and poulation dynamics is trending to synthetic opinion not only for analysis technique with stochastic nonlinear model but also for the correlating with theoretical research and field empirical data.