Smith Sarah A, de Oca Adrian Nieto Montes, Reeder Tod W, Wiens John J
Department of Ecology and Evolution, Stony Brook University, Stony Brook, New York 11794-5245, USA.
Evolution. 2007 May;61(5):1188-207. doi: 10.1111/j.1558-5646.2007.00085.x.
Differences in species richness at different elevations are widespread and important for conservation, but the causes of these patterns remain poorly understood. Here, we use a phylogenetic perspective to address the evolutionary and biogeographic processes that underlie elevational diversity patterns within a region. We focus on a diverse but well-studied fauna of tropical amphibians, the hylid frogs of Middle America. Middle American treefrogs show a "hump-shaped" pattern of species richness (common in many organisms and regions), with the highest regional diversity at intermediate elevations. We reconstructed phylogenetic relationships among 138 species by combining new and published sequence data from 10 genes and then used this phylogeny to infer evolutionary rates and patterns. The high species richness of intermediate elevations seems to result from two factors. First, a tendency for montane clades to have higher rates of diversification. Second, the early colonization of montane regions, leaving less time for speciation to build up species richness in lowland regions (including tropical rainforests) that have been colonized more recently. This "time-for-speciation" effect may explain many diversity patterns and has important implications for conservation. The results also imply that local-scale environmental factors alone may be insufficient to explain the high species richness of lowland tropical rainforests, and that diversification rates are lower in earth's most species-rich biome.
不同海拔地区物种丰富度的差异广泛存在且对生物保护具有重要意义，但这些模式的成因仍知之甚少。在此，我们从系统发育的角度来探讨一个地区内海拔多样性模式背后的进化和生物地理过程。我们聚焦于热带两栖动物中一个多样但研究充分的类群——中美洲雨蛙科蛙类。中美洲树蛙呈现出物种丰富度的“驼峰状”模式（在许多生物和地区都很常见），在中等海拔地区具有最高的区域多样性。我们通过整合来自10个基因的新的和已发表的序列数据，重建了138个物种之间的系统发育关系，然后利用这个系统发育关系来推断进化速率和模式。中等海拔地区较高的物种丰富度似乎源于两个因素。第一，山地分支具有更高多样化速率的趋势。第二，山地地区的早期定殖，使得在最近才被定殖的低地地区（包括热带雨林）积累物种丰富度的物种形成时间较少。这种“物种形成时间”效应可能解释了许多多样性模式，并且对生物保护具有重要意义。研究结果还表明，仅靠局部尺度的环境因素可能不足以解释低地热带雨林的高物种丰富度，而且在地球上物种最丰富的生物群落中，多样化速率较低。
