Data from: Effective size of density-dependent populations in fluctuating environments

Reliable estimates of effective population size Ne are of central importance in population genetics and evolutionary biology. For populations that fluctuate in size, harmonic mean population size is commonly used as a proxy for (multi-) generational effective size. This assumes no effects of density dependence on the ratio between effective and actual population size, which limits its potential application. Here we introduce density dependence on vital rates in a demographic model of variance effective size. We derive an expression for the ratio Ne/N in a density regulated population in a fluctuating environment. We show by simulations that yearly genetic drift is accurately predicted by our model, and not proportional to 1/(2N) as assumed by the harmonic mean model, where N is the total population size of mature individuals. We find a negative relationship between Ne/N and N. For a given N, the ratio depends on variance in reproductive success and the degree of resource limitation acting on the population growth rate. Finally, our model indicate that environmental stochasticity may affect Ne/N not only through fluctuations in N, but also for a given N at a given time. Our results show that estimates of effective population size must include effects of density dependence and environmental stochasticity.有效种群大小（effective population size, Ne）的可靠估计在种群遗传学与进化生物学中具有核心意义。对于种群规模存在波动的类群，种群大小的调和均值常被用作多世代有效种群大小的替代指标。该方法假设密度依赖对有效种群大小与实际种群大小的比值无影响，这限制了其应用潜力。本文在方差有效种群大小的种群统计模型中引入了生命率的密度依赖效应，推导得到了波动环境中密度调控种群的Ne/N比值表达式。通过模拟实验表明，本文模型可准确预测年度遗传漂变，且其与1/(2N)并不呈正比关系——这与调和均值模型的假设相悖，其中N代表成熟个体的总种群规模。我们发现Ne/N与N呈负相关关系；对于给定的N，该比值取决于繁殖成功率的变异以及作用于种群增长率的资源限制程度。最后，本模型表明环境随机性不仅可通过N的波动影响Ne/N，在给定时间且N固定的情况下同样会对其产生作用。本研究结果证实，有效种群大小的估计必须纳入密度依赖与环境随机性的效应。