Department of Ecology and Evolutionary Biology, University of Arizona, AZ 85721, USA.
Evolution. 2013 Jun;67(6):1715-28. doi: 10.1111/evo.12053. Epub 2013 Feb 8.
Deserts occupy approximately 12% of the Earth's land surface, and are thought to have species poor but highly specialized biotas. However, few studies have examined the evolutionary origins of desert biotas and of diversity patterns along aridity gradients. Further, it is unclear if species occurring in more extreme conditions on a given niche axis (i.e., precipitation) are more specialized for those conditions (i.e., have narrower niche breadths). We address these questions here using a time-calibrated phylogeny and climatic data for 117 species of phrynosomatid lizards. Phrynosomatids are the most species-rich family of lizards in North America, and are found from deserts to rainforests. Surprisingly, we find that phrynosomatids have higher richness in more arid environments. This pattern occurs seemingly because they have been present in more arid habitats longer (~55 million years), and lineages in mesic environments are recently derived from more arid-dwelling ancestors. We find little support for the hypothesis that species in more extreme environments are more specialized. Instead, many desert-dwelling species are broadly distributed, and species in the most mesic environments have the broadest niche breadths. In summary, phrynosomatids offer a counterexample to the idea that arid regions are inhabited by a small number of recent and highly specialized lineages.
沙漠占据了地球陆地表面的约 12%，被认为是物种贫乏但高度特化的生物区系。然而，很少有研究探讨过荒漠生物区系的进化起源以及干旱梯度上的多样性模式。此外，在给定的生态位轴（即降水）上，处于更极端条件下的物种是否更适应这些条件（即具有更窄的生态位宽度），这一点也不清楚。我们使用 117 种角蟾科蜥蜴的时间校准系统发育和气候数据来解决这些问题。角蟾科是北美的蜥蜴中物种最丰富的科，从沙漠到热带雨林都有分布。令人惊讶的是，我们发现角蟾科在更干旱的环境中具有更高的丰富度。这种模式似乎是因为它们在更干旱的栖息地中存在的时间更长（约 5500 万年），而在潮湿环境中的谱系是最近从更干旱的祖先中衍生出来的。我们几乎没有证据支持这样的假设，即处于更极端环境中的物种更加特化。相反，许多沙漠栖息物种分布广泛，而在最潮湿环境中的物种具有最宽的生态位宽度。总的来说，角蟾科为干旱地区由少数近期高度特化的谱系所占据的观点提供了一个反例。
