Rull Valentí
Departament de Biologia Animal, Vegetal i Ecologia, Universitat de Barcelona, Bellaterra, 08193, Barcelona, Spain.
Naturwissenschaften. 2004 Mar;91(3):139-42. doi: 10.1007/s00114-004-0504-1. Epub 2004 Feb 18.
The peculiar biogeography of the so-called "Lost World", i.e. the summits of sandstone tableaux ( tepuis) in the Neotropical Guyana region of Venezuela, has generated a debate regarding the factors that are thought to account for modern vegetation patterns in the region. Some argue that plant communities on these high-elevation summits reflect a long history of evolution in isolation, while others surmise that there has been substantial biotic interchange with the surrounding lowlands during glacial times. Until now, these apparently competing hypotheses have not been tested using palaeoecological methods. I used pollen analysis of Quaternary sediments and documented past vertical migrations of vegetation in response to climate changes, which supports the second hypothesis. Physiographical analysis, however, shows that about half the tableaux summits are too high for their flora to have reached the lowlands during the last glaciation, suggesting that a portion of the tableaux vegetation has always experienced some degree of biotic isolation. Thus, a component of the summit vegetation evolved in isolation, whereas other taxa experienced interchange, as reflected in endemism patterns among the tableaux summits. Biogeographical patterns on the summits are the result of complex evolutionary processes. The two hypotheses invoked to explain the vegetation patterns are not mutually exclusive, but instead complement one another.
所谓“失落世界”的独特生物地理学，即委内瑞拉新热带圭亚那地区砂岩台地（特普伊山）的山顶，引发了一场关于哪些因素被认为是该地区现代植被格局成因的争论。一些人认为，这些高海拔山顶上的植物群落反映了长期隔离进化的历史，而另一些人则推测，在冰川时期，与周边低地存在大量生物交流。到目前为止，这些明显相互矛盾的假说尚未通过古生态学方法进行验证。我对第四纪沉积物进行了花粉分析，并记录了植被过去因气候变化而发生的垂直迁移，这支持了第二种假说。然而，地形分析表明，约一半的台地山顶海拔过高，以至于其植物群在上次冰期时无法抵达低地，这表明部分台地植被一直处于某种程度的生物隔离状态。因此，山顶植被的一部分是在隔离状态下进化的，而其他分类群则经历了交流，这在台地山顶的特有种模式中有所体现。山顶的生物地理格局是复杂进化过程的结果。用于解释植被格局的这两种假说并非相互排斥，而是相互补充。
