Niche Evolution of South American Trees and its Consequences

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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.