Kozak Kenneth H, Wiens John J
Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY 11794-5245, USA.
Proc Biol Sci. 2007 Dec 7;274(1628):2995-3003. doi: 10.1098/rspb.2007.1106.
Many groups of organisms show greater species richness in the tropics than in the temperate zone, particularly in tropical montane regions. Forty years ago, Janzen suggested that more limited temperature seasonality in the tropics leads to greater climatic zonation and more climatic barriers to organismal dispersal along elevational gradients in the tropics relative to temperate regions. These factors could lead to differences in how species arise in tropical versus temperate regions and possibly contribute to greater tropical diversity. However, no studies have compared the relationships among climate, elevational distribution and speciation in a group inhabiting both tropical and temperate regions. Here, we compare elevational and climatic divergence among 30 sister-species pairs (14 tropical, 16 temperate) within a single family of salamanders (Plethodontidae) that reaches its greatest species richness in montane Mesoamerica. In support of Janzen's hypothesis, we find that sister species are more elevationally and climatically divergent in the tropics than in the temperate zone. This pattern seemingly reflects regional variation in the role of climate in speciation, with niche conservatism predominating in the temperate zone and niche divergence in the tropics. Our study demonstrates how latitudinal differences in elevational climatic zonation may increase opportunities for geographical isolation, speciation and the associated build-up of species diversity in the tropics relative to the temperate zone.
许多生物类群在热带地区的物种丰富度高于温带地区，尤其是在热带山地地区。四十年前，简森提出，相对于温带地区，热带地区温度季节性变化较小，导致气候分带更明显，沿海拔梯度的生物扩散面临更多气候障碍。这些因素可能导致热带地区和温带地区物种形成方式的差异，并可能促成更高的热带生物多样性。然而，尚无研究比较同时分布于热带和温带地区的某一生物类群中气候、海拔分布与物种形成之间的关系。在此，我们比较了蝾螈科（无肺螈科）一个家族中30对姊妹种（14对热带姊妹种、16对温带姊妹种）之间的海拔和气候差异，该家族在中美洲山地地区物种丰富度最高。为支持简森的假说，我们发现，与温带地区相比，热带地区的姊妹种在海拔和气候方面的差异更大。这种模式似乎反映了气候在物种形成过程中作用的区域差异，在温带地区生态位保守性占主导，而在热带地区生态位发生分化。我们的研究表明，相对于温带地区，热带地区海拔气候分带的纬度差异如何增加地理隔离、物种形成以及相关物种多样性积累的机会。
