Weir Jason T
Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
Evolution. 2006 Apr;60(4):842-55.
Late Pliocene and Pleistocene climatic instability has been invoked to explain the buildup of Neotropical biodiversity, although other theories date Neotropical diversification to earlier periods. If these climatic fluctuations drove Neotropical diversification, then a large proportion of species should date to this period and faunas should exhibit accelerated rates of speciation. However, the unique role of recent climatic fluctuations in promoting diversification could be rejected if late Pliocene and Pleistocene rates declined. To test these temporal predictions, dateable molecular phylogenies for 27 avian taxa were used to contrast the timing and rates of diversification in lowland and highland Neotropical faunas. Trends in diversification rates were analyzed in two ways. First, rates within taxa were analyzed for increasing or decreasing speciation rates through time. There was a significant trend within lowland taxa towards decreasing speciation rates, but no significant trend was observed within most highland taxa. Second, fauna wide diversification rates through time were estimated during one-million-year intervals by combining rates across taxa. In the lowlands, rates were highest during the late Miocene and then decreased towards the present. The decline in rates observed both within taxa and for the fauna as a whole probably resulted from density dependent cladogenesis. In the highlands, faunawide rates did not vary greatly before the Pleistocene but did increase significantly during the last one million years of the Pleistocene following the onset of severe glacial cycles in the Andes. These contrasting patterns of species accumulation suggest that lowland and highland regions were affected differently by recent climatic fluctuations. Evidently, habitat alterations associated with global climate change were not enough to promote an increase in the rate of diversification in lowland faunas. In contrast, direct fragmentation of habitats by glaciers and severe altitudinal migration of montane vegetation zones during climatic cycles may have resulted in the late Pleistocene increase in highland diversification rates. This increase resulted in a fauna with one third of its species dating to the last one million years.
上新世晚期和更新世的气候不稳定被用来解释新热带地区生物多样性的积累，尽管其他理论将新热带地区的多样化追溯到更早的时期。如果这些气候波动推动了新热带地区的多样化，那么很大一部分物种应该起源于这个时期，动物群应该表现出加速的物种形成速率。然而，如果上新世晚期和更新世的速率下降，那么近期气候波动在促进多样化方面的独特作用就可能被否定。为了检验这些时间预测，利用27个鸟类分类群的可测定年代的分子系统发育来对比低地和高地新热带动物群的多样化时间和速率。多样化速率的趋势通过两种方式进行分析。首先，分析分类群内的速率随时间的物种形成速率是增加还是减少。低地分类群内有一个显著的趋势是物种形成速率下降，但在大多数高地分类群内没有观察到显著趋势。其次，通过结合分类群的速率，在一百万年的时间间隔内估计整个动物群随时间的多样化速率。在低地，速率在中新世晚期最高，然后向现在下降。在分类群内和整个动物群中观察到的速率下降可能是由于密度依赖的分支进化。在高地，在更新世之前整个动物群的速率变化不大，但在安第斯山脉出现严重冰川周期后的更新世最后一百万年里显著增加。这些物种积累的对比模式表明，低地和高地地区受到近期气候波动的影响不同。显然，与全球气候变化相关的栖息地改变不足以促进低地动物群多样化速率的增加。相比之下，冰川导致的栖息地直接破碎以及气候周期中山区植被带的剧烈海拔迁移可能导致了更新世晚期高地多样化速率的增加。这种增加导致了一个动物群，其中三分之一的物种起源于最后一百万年。
