Clade-age-dependent diversification under high species turnover shapes species richness disparities among tropical rainforest lineages of Bulbophyllum (Orchidaceae)

Background: Tropical rainforests (TRFs) harbour almost half of the world’s vascular plant species diversity while covering only about 6–7% of land. However, why species richness varies amongst the Earth’s major TRF regions remains poorly understood. Here we investigate the evolutionary processes shaping continental species richness disparities of the pantropical, epiphytic and mostly TRF-dwelling orchid genus Bulbophyllum (c. 1,948 spp. in total; Asia-Pacific region: c. 1,564 spp.; Madagascar: 210; Africa: 80; Neotropics: 94) using diversification analyses based on a time-calibrated molecular phylogeny, coupled with ecological niche modelling (ENM) of geographic distributions under present and past (Last Glacial Maximum) conditions.
Results: Our results suggest an early-to-late Miocene scenario of ‘out-of-Asia-Pacific’ origin and progressive, dispersal-mediated diversification in Madagascar, Africa and the Neotropics, respectively. Species richness disparities amongst these four TRF ...