Wiens John J, Graham Catherine H, Moen Daniel S, Smith Sarah A, Reeder Tod W
Department of Ecology and Evolution, Stony Brook University, Stony Brook, New York 11794, USA.
Am Nat. 2006 Nov;168(5):579-96. doi: 10.1086/507882. Epub 2006 Sep 21.
Why are there more species in the tropics than in temperate regions? In recent years, this long-standing question has been addressed primarily by seeking environmental correlates of diversity. But to understand the ultimate causes of diversity patterns, we must also examine the evolutionary and biogeographic processes that directly change species numbers (i.e., speciation, extinction, and dispersal). With this perspective, we dissect the latitudinal diversity gradient in hylid frogs. We reconstruct a phylogeny for 124 hylid species, estimate divergence times and diversification rates for major clades, reconstruct biogeographic changes, and use ecological niche modeling to identify climatic variables that potentially limit dispersal. We find that hylids originated in tropical South America and spread to temperate regions only recently (leaving limited time for speciation). There is a strong relationship between the species richness of each region and when that region was colonized but not between the latitudinal positions of clades and their rates of diversification. Temperature seasonality seemingly limits dispersal of many tropical clades into temperate regions and shows significant phylogenetic conservatism. Overall, our study illustrates how two general principles (niche conservatism and the time-for-speciation effect) may help explain the latitudinal diversity gradient as well as many other diversity patterns across taxa and regions.
为什么热带地区的物种比温带地区的物种更多？近年来，这个长期存在的问题主要通过寻找多样性的环境相关因素来解决。但是，要理解多样性模式的根本原因，我们还必须研究直接改变物种数量的进化和生物地理过程（即物种形成、灭绝和扩散）。从这个角度出发，我们剖析了雨蛙科蛙类的纬度多样性梯度。我们重建了124种雨蛙科物种的系统发育树，估计了主要分支的分歧时间和多样化速率，重建了生物地理变化，并使用生态位建模来识别可能限制扩散的气候变量。我们发现雨蛙科起源于南美洲热带地区，直到最近才扩散到温带地区（物种形成的时间有限）。每个地区的物种丰富度与其被殖民的时间之间存在很强的关系，但分支的纬度位置与其多样化速率之间没有关系。温度季节性似乎限制了许多热带分支向温带地区的扩散，并表现出显著的系统发育保守性。总体而言，我们的研究说明了两个一般原则（生态位保守性和物种形成时间效应）如何有助于解释纬度多样性梯度以及跨分类群和地区的许多其他多样性模式。
