Showing papers by "Thomas L. P. Couvreur published in 2015"

Odd man out: why are there fewer plant species in African rain forests?

Abstract: Although tropical rain forests represent the most species-rich terrestrial ecosystem on the planet, the three main rain forest regions (Neotropics, South-East Asia and continental Africa) are not equally diverse. Africa has been labeled the “odd man out” because of its perceived lower species diversity when compared to the Neotropics or South-East Asia. Understanding why, within a biome, certain regions have higher or lower species diversity provides important insights into the evolution of biodiversity. I review the evidence in favor of an “odd man out” pattern and the different hypotheses that have been advanced to explain and test this pattern using recent ecological, biogeographical and diversification studies. The “odd man out” pattern has yet to be formally tested using extensive inventory plot data (including non woody species) between all three major rain forest regions based on appropriate statistics in an area controlled manner. The lower species diversity is not the result of a single cause, but is probably linked to numerous intricate causes related to present and past events. Future comparative studies should combine numerous variables including novel ones such at plant functional diversity. Finally, though more extinction in Africa is apparent from the fossil record, it is still hard to precisely quantify to what degree extinction varied between the three major regions. Diversification studies of important tropical plant lineages tend to support higher speciation rates in the Neotropics and South-East Asia instead of higher extinction in Africa as the main cause explaining the differences in species diversity. The lower species diversity of African rain forests remains an understudied question with numerous preconceived and largely untested ideas for which we are still far from having a synthetic explanation. This review highlights that there are still very little intercontinental rain forest comparisons of plant species diversity hindering any solid conclusions. To better address this, an integrative approach involving archeologists, climatologists and biologists coupled with data from all three regions should be privileged.

Five major shifts of diversification through the long evolutionary history of Magnoliidae (angiosperms)

Abstract: With 10,000 species, Magnoliidae are the largest clade of flowering plants outside monocots and eudicots. Despite an ancient and rich fossil history, the tempo and mode of diversification of Magnoliidae remain poorly known. Using a molecular data set of 12 markers and 220 species (representing >75% of genera in Magnoliidae) and six robust, internal fossil age constraints, we estimate divergence times and significant shifts of diversification across the clade. In addition, we test the sensitivity of magnoliid divergence times to the choice of relaxed clock model and various maximum age constraints for the angiosperms. Compared with previous work, our study tends to push back in time the age of the crown node of Magnoliidae (178.78-126.82 million years, Myr), and of the four orders, Canellales (143.18-125.90 Myr), Piperales (158.11-88.15 Myr), Laurales (165.62-112.05 Myr), and Magnoliales (164.09-114.75 Myr). Although families vary in crown ages, Magnoliidae appear to have diversified into most extant families by the end of the Cretaceous. The strongly imbalanced distribution of extant diversity within Magnoliidae appears to be best explained by models of diversification with 6 to 13 shifts in net diversification rates. Significant increases are inferred within Piperaceae and Annonaceae, while the low species richness of Calycanthaceae, Degeneriaceae, and Himantandraceae appears to be the result of decreases in both speciation and extinction rates. This study provides a new time scale for the evolutionary history of an important, but underexplored, part of the tree of angiosperms. The ages of the main clades of Magnoliidae (above the family level) are older than previously thought, and in several lineages, there were significant increases and decreases in net diversification rates. This study is a new robust framework for future investigations of trait evolution and of factors influencing diversification in this group as well as angiosperms as a whole.

Global diversification of a tropical plant growth form: environmental correlates and historical contingencies in climbing palms.

Abstract: Tropical rain forests (TRF) are the most diverse terrestrial biome on Earth, but the diversification dynamics of their constituent growth forms remain largely unexplored. Climbing plants contribute significantly to species diversity and ecosystem processes in TRF. We investigate the broad-scale patterns and drivers of species richness as well as the diversification history of climbing and non-climbing palms (Arecaceae). We quantify to what extent macroecological diversity patterns are related to contemporary climate, forest canopy height, and paleoclimatic changes. We test whether diversification rates are higher for climbing than non-climbing palms and estimate the origin of the climbing habit. Climbers account for 22% of global palm species diversity, mostly concentrated in Southeast Asia. Global variation in climbing palm species richness can be partly explained by past and present-day climate and rain forest canopy height, but regional differences in residual species richness after accounting for current and past differences in environment suggest a strong role of historical contingencies in climbing palm diversification. Climbing palms show a higher net diversification rate than non-climbers. Diversification analyses of palms detected a diversification rate increase along the branches leading to the most species-rich clade of climbers. Ancestral character reconstructions revealed that the climbing habit originated between early Eocene and Miocene. These results imply that changes from non-climbing to climbing habits may have played an important role in palm diversification, resulting in the origin of one fifth of all palm species. We suggest that, in addition to current climate and paleoclimatic changes after the late Neogene, present-day diversity of climbing palms can be explained by morpho-anatomical innovations, the biogeographic history of Southeast Asia, and/or ecological opportunities due to the diversification of high-stature dipterocarps in Asian TRFs.

Sirdavidia, an extraordinary new genus of Annonaceae from Gabon.

Abstract: A distinctive new monotypic genus from Gabon is described in the tropical plant family Annonaceae: Sirdavidia, in honor to Sir David Attenborough Molecular phylogenetic analyses confirm that Sirdavidia, which is very distinct from a morphological standpoint, is not nested in any existing genus of Annonaceae and belongs to tribe Piptostigmateae (subfamily Malmeoideae), which now contains a total of six genera The genus is characterized by long acuminate leaves, fully reflexed red petals, 16-19 bright yellow, loosely arranged stamens forming a cone, and a single carpel topped by a conspicuous stigma With just three known collections, a preliminary IUCN conservation status assessment is provided as "endangered" as well as a distribution map The discovery of Sirdavidia is remarkable at several levels First, it was collected near the road in one of the botanically best-known regions of Gabon: Monts de Cristal National Park Second, its sister group is the genus Mwasumbia, also monotypic, endemic to a small area in a forest in Tanzania, some 3000 km away Finally, the floral morphology is highly suggestive of a buzz pollination syndrome If confirmed, this would be the first documentation of such a pollination syndrome in Magnoliidae and early-diverging angiosperms in general