Institute of Botany, University of Liège, 4000, Liège, Belgium.
Departmento de Ciências Agrárias, Azorean Biodiversity Group (CITA-A) and Platform for Enhancing Ecological Research & Sustainability (PEERS), Universidade dos Açores, 9700-042 Angra do Heroísmo, Terceira, Açores, Portugal.
New Phytol. 2014 Jan;201(1):305-311. doi: 10.1111/nph.12480. Epub 2013 Sep 6.
A fundamental challenge to our understanding of biodiversity is to explain why some groups of species diversify, whereas others do not. On islands, the gradual evolution of a new species from a founder event has been called 'anagenetic speciation'. This process does not lead to rapid and extensive speciation within lineages and has received little attention. Based on a survey of the endemic bryophyte, pteridophyte and spermatophyte floras of nine oceanic archipelagos, we show that anagenesis, as measured by the proportion of genera with single endemic species within a genus, is much higher in bryophytes (73%) and pteridophytes (65%) than in spermatophytes (55%). Anagenesis contributed 49% of bryophyte and 40% of endemic pteridophyte species, but only 17% of spermatophytes. The vast majority of endemic bryophytes and pteridophytes are restricted to subtropical evergreen laurel forests and failed to diversify in more open environments, in contrast with the pattern exhibited by spermatophytes. We propose that the dominance of anagenesis in island bryophytes and pteridophytes is a result of a mixture of intrinsic factors, notably their strong preference for (sub)tropical forest environments, and extrinsic factors, including the long-term macro-ecological stability of these habitats and the associated strong phylogenetic niche conservatism of their floras.
生物多样性的一个基本挑战是解释为什么有些物种群体多样化，而有些则不然。在岛屿上，由创始事件逐渐进化为新物种的过程被称为“渐成性物种形成”。这个过程不会导致谱系内的快速和广泛的物种形成，因此受到的关注较少。基于对九个大洋群岛特有苔藓植物、蕨类植物和种子植物区系的调查，我们表明，渐成性物种形成（通过属内具有单一特有种的属的比例来衡量）在苔藓植物（73%）和蕨类植物（65%）中比在种子植物（55%）中高得多。渐成性物种形成贡献了 49%的苔藓植物和 40%的特有蕨类植物物种，但只贡献了 17%的种子植物物种。绝大多数特有苔藓植物和蕨类植物仅限于亚热带常绿月桂林，而未能在更开放的环境中多样化，这与种子植物的模式形成鲜明对比。我们提出，岛屿苔藓植物和蕨类植物中渐成性物种形成的主导地位是内在因素和外在因素混合作用的结果，内在因素包括它们对（亚热带）森林环境的强烈偏好，外在因素包括这些栖息地的长期宏观生态稳定性以及它们的区系的强烈系统发育生态位保守性。
