Yuan Chi, Chesson Peter
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, United States.
Theor Popul Biol. 2015 Nov;105:39-52. doi: 10.1016/j.tpb.2015.08.001. Epub 2015 Aug 22.
Although it is likely that many coexistence mechanisms contribute to maintenance of species diversity, most approaches to understanding species coexistence proceed as if only one mechanism would be present. In studies of species coexistence in a temporally fluctuating environment, the storage effect, believed to be the most important coexistence mechanism, has been the focus. Although a different coexistence mechanism--relative nonlinearity--is also predicted to arise frequently with environmental variation, its effect has been overshadowed by the storage effect. The relatively nonlinear growth rates on which the mechanism depends arise simply from differences in life history traits. Many kinds of temporal variation can then interact with these nonlinearity differences to create the relative nonlinearity coexistence mechanism. Much is unknown about when this mechanism is important and its total neglect is not justified. Here, we use the lottery model to provide a much needed quantitative assessment of the relative and combined effects of relative nonlinearity and the storage effect. Our analysis takes advantage of recently developed techniques for quantifying coexistence mechanisms when multiple mechanisms operate in concert. We find that relative nonlinearity is able to contribute substantially to species coexistence in the lottery model when two conditions are satisfied: (1) species must differ greatly in their adult death rates, (2) sensitivity of recruitment to environmental variation must be greater for species with larger adult death rates. In addition, relative nonlinearity has a critical role in compensating for a weakened storage effect when there is high correlation between species in their responses to the varying environment. In some circumstances relative nonlinearity is stronger than the storage effect or is even the sole mechanism of coexistence.
尽管可能有许多共存机制有助于维持物种多样性，但大多数理解物种共存的方法在进行时都假定只有一种机制存在。在对时间波动环境中物种共存的研究中，被认为是最重要共存机制的存储效应一直是焦点。尽管另一种共存机制——相对非线性——也预计会随着环境变化频繁出现，但其影响一直被存储效应所掩盖。该机制所依赖的相对非线性增长率仅仅源于生活史特征的差异。然后，许多种时间变化可以与这些非线性差异相互作用，从而产生相对非线性共存机制。关于这种机制何时重要还有很多未知之处，完全忽视它是不合理的。在这里，我们使用抽签模型对相对非线性和存储效应的相对及综合影响进行了急需的定量评估。我们的分析利用了最近开发的技术，用于在多种机制协同运作时量化共存机制。我们发现，当满足两个条件时，相对非线性能够在抽签模型中对物种共存做出重大贡献：（1）物种的成年死亡率必须有很大差异，（2）成年死亡率较高的物种，其补充对环境变化的敏感性必须更大。此外，当物种对变化环境的响应之间存在高度相关性时，相对非线性在补偿减弱的存储效应方面具有关键作用。在某些情况下，相对非线性比存储效应更强，甚至是唯一的共存机制。
