The historical assembly of plant communities

PoissoniaPhylogenies of the seasonally dry tropical dry forest genera Ruprecthia (Polygonaceae), Coursetia, Poissonia, Chaetocalyx, Nissolia (all Leguminosae) and Loxopterygium (Anacardiaceae) show relatively old diversifications and a high degree of geographical phylogenetic structure where related species are found in the same or adjacent areas. This contrasts with more recent speciation patterns of the rain forest genera Inga and Renealmia, whose phylogenies shows low geographic phylogenetic structure. Phylogenies of some legume genera also suggest that the woody flora of the tropical savannas [t1] Link to of Latin America has originated by multiple speciation events from lineages in surrounding rain forest and dry forest biomes. These savanna lineages have gained on multiple, independent occasions the necessary adaptations such as corky bark and root-sprouting that are necessary to survive the frequent fires experienced in the savannas. In contrast, our phylogenies suggest that it may be more difficult to evolve the adaptations needed to survive the erratic droughts in dry forests.

Collectively, all these studies suggest that the historical assembly of neotropical dry forest, savanna and rain forest communities may be different, and, in collaboration with the University of Leeds, we have received a major grant from the Natural Environment Research Council to investigate this proposition more thoroughly. 

Our research united networks of existing tree inventories, covering more than 1000 sites across the three major biomes of tropical South America: rain forests, dry forests and savannas. We are linking these data with new information, derived from DNA sequence data, on the evolutionary relationships of the woody plants in these biomes. The project includes a special focus on species on the legume family, which is dominant in all three biomes. We are investigating how often, and when in evolutionary history, lineages of trees have shifted from one biome to another, which will, in turn, 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, especially for savannas and dry forests. We hope that our research will highlight the importance and plight of tropical dry forests and savannas, characterised by many decision makers and commentators as fair game for destruction if this might save rain forest areas.

The ability of plants to make major ecological shifts governs their response to changing geological or climatic conditions. In the face of aridification, for example, plants adapted to wet forest would either have to adapt to the changing conditions or shift their distributions. Our research aims to determine the extent to which plants exhibit phylogenetic niche conservatism, i.e. an inability to adapt to changing environmental conditions which would be reflected in the fact that closely related species occupy similar ecological niches. Determining the extent of phylogenetic niche conservatism will allow us to make better predictions on how plants will react to future climate change. 

Recent publications

Pennington, R.T., Lavin, M & Oliveira-Filho A. (2009). Plant diversity, evolution and ecology in the tropics: perspectives from seasonally dry tropical forests. Annual Review of Ecology and Systematics 40: 437-457.

Simon, M., Grether, R., de Queiroz L.P., Skema C., Pennington, R.T. & C.E. Hughes. (2009). Recent assembly of the Cerrado, a neotropical plant diversity hotspot, by in-situ evolution of adaptations to fire. Proceedings of the National Academy of Sciences, USA 106:  20359-20364.

Pennington R.T., Lavin M, Hughes C., Sarkinen T, Lewis G, Klitgaard B. (2010). Differing diversification histories in the Andean biodiversity hotspot. Proceedings of the National Academy of Sciences, USA 107: 13783-13787.

 Dick C.W. & Pennington, R.T. (2011). Molecular systematic perspectives on biome origins and dynamics. New Phytologist 193(1): 9-11.

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