Niche Evolution of South American Trees and its Consequences

摘要(普通读者，4000字)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组成和物种丰富度差异的进化过程知之甚少。了解这些过程具有基本和实际的重要性--例如，规划保护战略越来越多地使用关于进化关系的信息，作为确定关于单个物种的优先决策的一部分。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才刚刚开始揭示物种之间的进化关系。因此，通过土地利用或气候变化造成的威胁对保护这些社区的进化史的影响几乎完全未知。我们的研究将利用令人印象深刻的现有树木清单数据，覆盖南美洲热带三大生物群的1000多个地点：热带雨林、干燥森林和稀树草原。我们将使用DNA序列数据，将这些数据与所有属和豆科所有物种的进化关系的新信息联系起来，豆科在所有三个生物群中都占主导地位。属级别的进化树将允许我们深入进化时间进行分析，而物种级别的豆科树将提供最近进化的视图。我们将调查树木的谱系在不同的生物群之间切换了多少次，这将为保护和未来进化多样化的研究提供重要的知识。如果血统很少在生物群之间切换，那么每个生物群将包含进化多样性的一个独特的子集，单个生物群的破坏可能会抹去整个进化历史的一部分。这种破坏整个生物群的情况并不是不可能的。这项提议的一个重要方面是，它将不仅关注亚马逊盆地的热带雨林，还将考虑被遗忘的树木主导的稀树草原和热带干燥森林的生物群落。这些地层应该得到科学家和自然资源保护者的更多关注，因为它们物种丰富，遭受了更大的破坏--巴西原始200万平方公里的稀树草原中，超过70%已经被破坏，而亚马逊地区约70%的面积完好无损。热带干燥森林是世界上最受威胁的热带森林类型，在许多地区只剩下不到5%的森林。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将其描述为一文不值--如果这可以拯救热带雨林地区，那就是公平的破坏游戏--例如最近发表在“经济学人”杂志上的一篇文章(2010年8月28日；巴西的农业奇迹：种植平原，拯救森林；http://www.economist.com/node/16889019).In除了生物群的切换外，我们还将调查这些群体在进化过程中如何适应特定的气候和土壤条件)。这项工作将使我们能够理解驱动我们观察到的生物群移位的过程。此外，这些分析可能有助于理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变化，很少相关的物种将倾向于具有相似的气候生态位，并且相关物种的整个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预测的气候和土地利用变化情景下，不同生物群中进化多样性丧失的影响。我们的结果将对南美洲国家政府机构和国际组织(如世界自然基金会)制定热带保护优先事项的保护规划具有重要意义。

Summary (for general audience, 4000 characters)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.