Phillimore Albert B, Orme C David L, Davies Richard G, Hadfield Jarrod D, Reed William J, Gaston Kevin J, Freckleton Robert P, Owens Ian P F
Division of Biology and Natural Environment Research Council Centre for Population Biology, Imperial College London, Silwood Park Campus, Ascot, Berkshire SL5 7PY, United Kingdom.
Evolution. 2007 Apr;61(4):942-57. doi: 10.1111/j.1558-5646.2007.00068.x.
Theory predicts that biogeographic factors should play a central role in promoting population divergence and speciation. Previous empirical studies into biogeography and diversification have been relatively restricted in terms of the geographical area, phylogenetic scope, and the range of biogeographic factors considered. Here we present a global analysis of allopatric phenotypic divergence (measured as subspecies richness) across more than 9600 bird species. The main aim of this study was to examine the extent to which biogeographical factors can explain patterns of phenotypic divergence. Analysis of the taxonomic distribution of subspecies among species suggests that subspecies formation and extinction have occurred at a considerably faster rate than has species formation. However, the observed distribution departs from the expectation under a random birth-death model of diversification. Across 19 phylogenetic trees, we find no significant linear relationship between species age and subspecies richness, implying that species age is a poor predictor of subspecies richness. Both subspecies richness and subspecies diversification rate are found to exhibit low phylogenetic signal, meaning that closely related species do not tend to possess similar numbers of subspecies. As predicted by theory, high subspecies richness was associated with large breeding range size, island dwelling, inhabitation of montane regions, habitat heterogeneity, and low latitude. Of these factors, breeding range size was the variable that explained the most variation. Unravelling whether species that have invaded previously glacial areas have more or fewer subspecies than expected proves to be complicated due to a covariation between the postglacial colonization, latitude, geographic range size, and subspecies richness. However, the effect of postglacial colonization on subspecies richness appears to be small. Mapping the distribution of species' subspecies richness globally reveals geographical patterns that correspond to many of the predictions of the statistical models, but may also reflect geographical variation in taxonomic practice. Overall, we demonstrate that biogeographic models can explain about 30% of the global variation in subspecies richness in birds.
理论预测，生物地理因素在促进种群分化和物种形成过程中应发挥核心作用。先前对生物地理学与物种多样化的实证研究，在地理区域、系统发育范围以及所考虑的生物地理因素范围方面都相对有限。在此，我们对9600多种鸟类的异域表型分化（以亚种丰富度衡量）进行了全球分析。本研究的主要目的是检验生物地理因素能在多大程度上解释表型分化模式。对物种中亚种的分类分布分析表明，亚种的形成和灭绝速度比物种形成速度要快得多。然而，观察到的分布偏离了多样化随机生死模型下的预期。在19个系统发育树中，我们发现物种年龄与亚种丰富度之间不存在显著的线性关系，这意味着物种年龄对亚种丰富度的预测能力较差。我们发现亚种丰富度和亚种多样化率均表现出较低的系统发育信号，这意味着亲缘关系较近的物种往往不具有相似数量的亚种。正如理论所预测的，高亚种丰富度与大繁殖范围、岛屿栖息、山地地区栖息、栖息地异质性以及低纬度相关。在这些因素中，繁殖范围是解释变异最多的变量。由于冰期后殖民化、纬度、地理范围大小和亚种丰富度之间的协变关系，要弄清楚入侵过先前冰川地区的物种的亚种数量是否比预期的多还是少，结果证明是复杂的。然而，冰期后殖民化对亚种丰富度的影响似乎较小。绘制全球物种亚种丰富度分布图，揭示了与统计模型的许多预测相对应的地理模式，但也可能反映了分类学实践中的地理差异。总体而言，我们证明生物地理模型可以解释鸟类亚种丰富度全球变异的约30%。
