Although it is clear that climatic changes can cause species extinctions, it has been far more controversial whether these changes have driven species production in tropical forests. Our work demonstrates that geologically recent climatic changes during the Ice Ages co-incide with species production in several groups of tropical rain forest herbs and trees. For example, the many species of the c. 300 in the neotropical legume tree genus Inga (300 spp.) arose during this time, and we have demonstrated similarly recent speciation in Aframomum (Zingiberaceae), and to some extent in Begonia and Cyrtandra (Gesneriaceae). Whilst these results cannot prove that climate changes have driven speciation, they are consistent with this idea, and contradict many animal studies that show speciation patterns to have pre-dated the Pleistocene.
In neotropical seasonally dry forests, we have investigated whether past climate changes have influenced the distribution of tree species characteristic of this biome. We are analysing large floristic inventory datasets gathered by RBGE scientists and collaborators to see if levels of floristic similarity between isolated seasonal forest areas are consistent with recent connections in times of drier climates. In collaboration with Geneva Botanical Garden, we are using molecular population genetic techniques to investigate how the distributions of two widespread South American dry forest tree species (Geoffroea spinosa and Astronium urundeuva) have been generated. In Streptocarpus, we have shown that species ranges in Africa have been heavily influenced by recent historical climate changes.
Recent phylogenetic work on the legume genus Inga has been in collaboration with the ecologists Phyllis Coley and Thomas Kursar (University of Utah, USA and Smithsonian Tropical Research Institute, Panama) who are using Inga as a model for studying the evolutionary ecology of anti-herbivory strategies in tropical plants. Inga species use two strategies to avoid herbivores: some have young leaves that expand and lignify quickly to shorten the time of vulnerability to insect herbivores, but have few chemical defences ("escape strategy"); others have young leaves that expand slowly, but have secondary chemistry that deters herbivores ("defence strategy"). Mapping these strategies onto a resolved phylogeny of Inga species would enable a test of whether the evolution of antiherbivory strategies has been associated with the remarkably rapid speciation of the genus.
Recent publications
Coley, P. D., Lokvam, J., Rudolph, K., Bromberg, K., Wright, L., Dvorett, D., Ring, S., Ponge, A., Baptiste, C., Pennington, R. T. & Kursar, T. A. (2005). Divergent defensive strategies of young leaves in two Neotropical species of Inga. Ecology 86: 2633-2643.
Hughes, M., Möller, M., Bellstedt, D.U., Edwards, T.J & de Villiers, M. (2005). Refugia, dispersal and divergence across a forest archipelago: a study of Streptocarpus in eastern South Africa. Molecular Ecology, 14: 4415-4426.
Pennington, R.T., Lavin, M. Prado, D.E., Pendry, C.A., Pell, S. & Butterworth, C.A. (2004). Historical climate change and speciation: Neotropical seasonally dry forest plants show patterns of both Tertiary and Quaternary diversification. Philosophical Transactions of the Royal Society (Biological Sciences)359: 515-538.
Richardson, J.E., Pennington, R.T., Pennington, T.D. & Hollingsworth, P.H. (2001). Rapid diversification of a species-rich genus of Neotropical rain forest trees. Science 293: 2242-2245