Species competition takes place in a fluctuating environment, so the selective forces on different populations vary through time. In many realistic situations the mean fitness and the amplitude of its temporal variations are abundance-dependent. Here we present a theory of two-species competition with abundance-dependent stochastic fitness variations and solve for the chance of ultimate fixation, the time to absorption and the time to fixation. We then examine the ability of this two-species system to serve as an effective model for high-diversity assemblages and to account for the presence of an intra-specific differential response to environmental variations. The effective model is shown to capture the main features of competition between composite populations.

物种竞争发生在一个波动的环境中，因此不同种群的选择力随时间而变化。在许多现实情况下，平均适应度及其时间变化的幅度与丰度有关。在这里，我们提出了一种具有丰度相关随机适应度变化的两种物种竞争理论，并解决了最终固定的机会、吸收时间和固定时间。然后，我们检查了这个两个物种系统作为高多样性组合的有效模型的能力，并解释了对环境变化的种内差异反应的存在。显示有效模型可以捕捉复合种群之间竞争的主要特征。