The affecting of demographic stochasticity and environmental stochasticity to population extinction
种群统计随机性和环境随机性对种群绝灭的影响

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.