Neutral models in ecology assume that all species are demographically equivalent, such that their abundances differ ultimately because of demographic stochasticity rather than selection. In spite of their simplicity, neutral models have been found to accurately reproduce static patterns of biodiversity for diverse communities. However, the same neutral models have been found to exhibit species abundance dynamics that are far too slow compared to reality, resulting in poor fits to temporally dynamic patterns of biodiversity. Here, we show that one of the root causes of these slow dynamics is the additional assumption that a community has reached an equilibrium with a fixed community size, with species that have a net growth rate close to zero. We removed this additional assumption by constructing and analyzing a neutral model with an expected community size that can change over time and is not necessarily at equilibrium, which thus allows the historical formation of a community to be represented explicitly. Our analysis demonstrated that for the general scenario where a small community rapidly grows in size to a carrying capacity, representing recovery from ecological disturbance or assembly of a new community, the model produced much larger changes in species abundances and much shorter species ages than a neutral model at an equilibrium with fixed community size. In addition, the species abundance distribution was biphasic with a subset of abundant species arising from a founder effect. We confirmed these new results in applications of the new model to the specific scenario of recovery of the Amazon tree community after the end-Cretaceous bolide impact, which involved periods of increasing and decreasing community size. We conclude that incorporating transient dynamics in neutral models improves realism by allowing explicit consideration of how a community is formed over realistic time-scales.

生态学中的中性模型假设所有物种在人口统计上都是等同的，因此它们的丰度最终因人口统计随机性而不是选择而不同。尽管它们很简单，但已发现中性模型可以准确地再现不同社区的生物多样性静态模式。然而，已发现相同的中性模型显示的物种丰度动态与现实相比太慢，导致与生物多样性的时间动态模式的拟合不佳。在这里，我们表明这些缓慢动态的根本原因之一是额外的假设，即社区已经达到平衡，社区规模固定，物种的净增长率接近于零。我们通过构建和分析一个具有预期社区规模的中性模型来消除这个额外的假设，该模型可以随时间变化并且不一定处于平衡状态，从而允许明确地表示社区的历史形成。我们的分析表明，对于小型社区的规模迅速增长到承载能力的一般情况，代表从生态干扰或新社区的聚集中恢复，该模型产生了比中性的物种丰度更大的变化和更短的物种年龄具有固定社区大小的均衡模型。此外，物种丰度分布是双相的，其中一部分丰富的物种是由奠基者效应引起的。我们在将新模型应用于白垩纪末期火流星撞击后亚马逊树群落恢复的特定情景中证实了这些新结果，该情景涉及群落规模增加和减少的时期。我们得出结论，通过允许明确考虑社区如何在现实时间尺度上形成，将瞬态动力学纳入中性模型可以提高现实主义。