Santa Fe Institute, Santa Fe, New Mexico 87501, USA.
Am Nat. 2009 Feb;173(2):256-63. doi: 10.1086/595760.
Within large taxonomic assemblages, the number of species with adult body mass M is characterized by a broad but asymmetric distribution, with the largest mass being orders of magnitude larger than the typical mass. This canonical shape can be explained by cladogenetic diffusion that is bounded below by a hard limit on viable species mass and above by extinction risks that increase weakly with mass. Here we introduce and analytically solve a simplified cladogenetic diffusion model. When appropriately parameterized, the diffusion-reaction equation predicts mass distributions that are in good agreement with data on 4,002 terrestrial mammals from the late Quaternary and 8,617 extant bird species. Under this model, we show that a specific trade-off between the strength of within-lineage drift toward larger masses (Cope's rule) and the increased risk of extinction from increased mass is necessary to produce realistic mass distributions for both taxa. We then make several predictions about the evolution of avian species masses.
在大型分类组合中，具有成体质量 M 的物种数量的分布特征是广泛的，但不对称的，最大质量比典型质量大几个数量级。这种典型的形状可以通过分支扩散来解释，分支扩散的下限受到可行物种质量的硬性限制，上限则受到与质量呈弱相关的灭绝风险的限制。在这里，我们引入并分析了解决简化分支扩散模型。当适当地参数化时，扩散反应方程预测的质量分布与来自晚第四纪的 4002 种陆地哺乳动物和现存的 8617 种鸟类的数据非常吻合。在这个模型下，我们表明，在线内漂移向更大质量的强度（科普及规则）和因质量增加而增加的灭绝风险之间的特定权衡，对于产生这两个分类单元的现实质量分布是必要的。然后，我们对鸟类物种质量的演化做出了几个预测。
