Niche evolution of South American trees and its consequences

热带植物群落以其高度多样性而闻名，但我们对造成不同类型热带生态系统在组成和物种丰富度方面存在巨大差异的进化过程知之甚少。理解这些过程具有基本的和实际的重要性——例如，规划保护策略越来越多地使用进化关系的信息作为对单个物种优先决策的一部分。然而，对于热带植物群落来说，基于DNA序列的足够大的数据集只是刚刚开始揭示物种之间的进化关系。因此，无论是通过土地利用还是气候变化，威胁对保护这些群落的进化史的影响仍然几乎完全未知。我们的研究将利用令人印象深刻的现有树木库存数据，覆盖热带南美洲三个主要生物群落的1000多个地点：雨林，干燥森林和稀树草原。我们将利用DNA序列数据将这些数据与豆科所有属和所有种的进化关系的新信息联系起来，豆科在所有三个生物群系中都占主导地位。属水平的进化树将使我们能够深入分析进化时间，而种水平的豆科植物树将提供最近进化的观点。我们将调查树木的谱系在不同的生物群系之间切换了多少次，这将为保护和未来的进化多样化研究提供重要的知识。如果谱系很少在生物群系之间切换，那么每个生物群系将包含一个独特的进化多样性子集，单个生物群系的破坏可能会抹去整个进化史。这种破坏整个生物群落的情景并非不可能发生。该提案的一个重要方面是，它将不仅仅关注亚马逊盆地的雨林，还将考虑被遗忘的以树木为主的稀树草原和热带干燥森林的生物群落。这些地层值得科学家和自然资源保护主义者给予更多的关注，因为它们物种丰富，并且遭受了更大的破坏——巴西原始200万平方公里的热带稀树草原中有70%以上已经被破坏，而亚马逊河流域的70%左右是完整的。热带干林是世界上受威胁最严重的热带森林类型，在许多地区仅存不到5%。我们相信我们的研究将突出热带干燥森林和稀树草原的重要性和困境，许多决策者和评论员认为它们毫无价值——如果这样做可以拯救热带雨林地区，就可以破坏它们——《经济学人》杂志最近的一篇文章（2010年8月28日）举例说明了这一点；巴西的农业奇迹：种植平原，拯救森林；http://www.economist.com/node/16889019).In除了生物群落转换，我们还将研究这些群体在进化过程中对特定气候和土壤条件的适应是如何变化的。这项工作将使我们能够理解驱动我们观察到的生物群落变化的过程。此外，这些分析可能有助于了解气候变化将如何影响群落：例如，如果物种的气候偏好发生不频繁的变化，相关物种将倾向于具有相似的气候生态位，并且整个相关物种群体可能容易因特定的气候变化轨迹而灭绝。我们研究的最后阶段将研究在气候和土地利用变化的预测情景下，不同生物群落中进化多样性丧失的影响。我们的研究结果将与南美洲国家政府机构和国际组织（如世界自然基金会）的保护规划有关，这些组织参与制定热带保护的优先事项。

Tropical plant communities are famed for their high diversity but we still have little knowledge about the evolutionary processes that have created wide differences in the composition and species richness of different kinds of tropical ecosystem. Understanding these processes is of fundamental and practical importance - for example, planning conservation strategies increasingly uses information on evolutionary relationships as part of prioritising decisions about individual species. However, for tropical plants communities, sufficiently large datasets based on DNA sequences are only just beginning to reveal the evolutionary relationships between species. As a result, the implications of threats, either through land-use or climate change, for the conservation of the evolutionary history of these communities remains almost entirely unknown. Our research will take advantage of impressive existing data of tree inventories, covering more than 1000 sites in three major biomes in tropical South America: rain forests, dry forests and savannas. We will link these data with new information on the evolutionary relationships of all genera, and all species of the legume family, which is dominant in all three biomes, using DNA sequence data. A genus-level evolutionary tree will allow us to make analyses deep into evolutionary time, whereas a species-level legume tree will give a view of recent evolution. We will investigate how many times lineages of trees have switched between the different biomes, which will deliver important knowledge for conservation and future studies of evolutionary diversification. If lineages have rarely switched between biomes, then each biome will contain a distinct subset of evolutionary diversity, and destruction of a single biome could wipe out an entire part of evolutionary history.Such scenarios of the destruction of an entire biome are not unlikely. One important aspect of this proposal is that it will not focus solely on the rain forests of the Amazon Basin, but will also consider the forgotten biomes of tree-dominated savannas and tropical dry forests. These formations deserve greater attention from scientists and conservationists because they are species-rich, and have suffered greater destruction - more than 70% of the original two million km2 of the Brazilian savannas have been destroyed, whereas c. 70% of Amazonia is intact. Tropical dry forests, of which less than 5% remain in many areas, are the most threatened tropical forest type in the world. We believe our research will highlight the importance and plight of tropical dry forests and savannas, characterised by many decision makers and commentators as worthless - fair game for destruction if this might save rain forest areas - exemplified by a recent leader in the Economist magazine (28.08.2010; Brazil's agricultural miracle: Plant the plains, save the forests; http://www.economist.com/node/16889019).In addition to biome switching, we will also investigate how adaptations to specific climatic and soil conditions have changed during evolution in these groups. This work will enable us to understand the processes driving the biome shifts we observe. In addition, these analyses may help to understand how climate change will affect communities: for example, if changes in climatic preferences of species have occurred infrequently related species will tend to have similar climatic niches, and whole groups of related species might be vulnerable to extinction from particular trajectories of climate change.The final stage of our study will examine the implications for loss of evolutionary diversity in different biomes under projected scenarios of climate and land-use change. Our results will be of relevance to conservation planning by national government agencies in South America and international organisations, such as the WWF, involved in setting priorities for tropical conservation.