Why are tropical rainforests so diverse?
Tropical rainforests have the largest number of species on Earth and an astonishing variation of life forms, such as climbing palms. A new study led by Daniel Kissling of the Institute for Biodiversity and Ecosystem Dynamics (IBED) and his French colleague Thomas Couvreur of the Institut de Recherche pour le Développement in Montpellier explored why climbing palms have become so diverse. These findings have recently been published in the open-access journal ‘Frontiers in Genetics'.
Rainforest are diverse and their plant composition is characterized by an immense diversity of canopy trees, small trees and shrubs in the understory, climbers (lianas and vines), and numerous epiphytes and other parasitic plants. Understanding how these various growth forms have become so diverse provides important insights into the evolution, ecology and conservation of tropical rainforests
Climbing palms as a model system
Palms are typical for tropical rainforests and they are found on all continents. With about 2500 species, they are diverse and most of them occur in South America or Southeast Asia. Climbing is a strategy that allows plants to reach light with minimal investment into support structures such as stems. In palms, climbers make up about 20% of all palms (>500 species), but in contrast to other palms they are mainly distributed in Southeast Asia and less in South America or Africa. Why? Many palms found in Southeast Asia have developed a unique climbing organ (the flagellum) which provides an effective mechanism to reach the upper canopy for their much-needed doses of light. This morphological novelty might have been particularly useful in the rainforests of Southeast Asia because they are dense and relatively tall due to the presence of a specific family of rainforest trees (Dipterocarpaceae). Using phylogenetic data, Kissling and colleagues showed that climbing palms have diversified more than non-climbing palms. The climbing habit in palms has evolved seven times, with the two most important adaptations 50 and 40 million years ago. This suggests that the change from a non-climbing to a climbing habit has partly promoted the high diversity of palms that we see in rainforests today.
Focus of research team
The factors that determine the origin and maintenance of biodiversity are the focus of Kissling’s research team. ‘Especially in the tropics, where most of the biodiversity is located and at the same time highly threatened, we still know surprisingly little about the ecology and evolution of species’, says Kissling. ‘We therefore use large datasets of species distributions and ecological traits together with environmental data and phylogenies to better understand the distribution of life on Earth. This research is not only important for understanding the past history of tropical rainforests but also for predicting the future of biodiversity in response to climate and land use change’.
Couvreur, T.L.P., Kissling, W.D., Condamine, F.L., Svenning, J.-C., Rowe, N.P. & Baker, W.J. (2015) Global diversification of a tropical plant growth form: environmental correlates and historical contingencies in climbing palms. Frontiers in Genetics, 5, 452.