Nature2014-06-18 3:34 PM

新物种的形成需要新的生境 Niche filling slows the diversification of Himalayan songbirds

论文摘要 

适应性辐射和物种形成的开始问题已得到广泛研究(如对达尔文云雀 、棘鱼和慈鲷(丽鱼)所做的研究),但我们对接着将会发生什么相对来说却知之甚少。尤其是,对新物种的确立来说,哪一步是限制物种形成速度的?对在喜马拉雅山坡上所见的358种鸣禽所做的这项为期七年的研究表明,限制多样化的是新生境形成和被占据的速度,而不是新物种通过生殖隔离来形成的速度。

Abstract 

Speciation generally involves a three-step process—range expansion, range fragmentation and the development of reproductive isolation between spatially separated populations. Speciation relies on cycling through these three steps and each may limit the rate at which new species form. We estimate phylogenetic relationships among all Himalayan songbirds to ask whether the development of reproductive isolation and ecological competition, both factors that limit range expansions, set an ultimate limit on speciation. Based on a phylogeny for all 358 species distributed along the eastern elevational gradient, here we show that body size and shape differences evolved early in the radiation, with the elevational band occupied by a species evolving later. These results are consistent with competition for niche space limiting species accumulation. Even the elevation dimension seems to be approaching ecological saturation, because the closest relatives both inside the assemblage and elsewhere in the Himalayas are on average separated by more than five million years, which is longer than it generally takes for reproductive isolation to be completed; also, elevational distributions are well explained by resource availability, notably the abundance of arthropods, and not by differences in diversification rates in different elevational zones. Our results imply that speciation rate is ultimately set by niche filling (that is, ecological competition for resources), rather than by the rate of acquisition of reproductive isolation.

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