History or Ecology? Untangling the Drivers of Diversification in the Tropics.

Some clades of trees within tropical forests achieve spectacular diversity.  Why have some tree groups diversified so much whereas others have far lower diversity? This project will test a novel hypothesis to explain this enduring mystery: across the tropics, diversification has been greatest in lineages that share ecological traits that promote speciation and reduce extinction rates.

Two mechanisms drive diversification: ‘extrinsic’ processes, such as tectonic events and dispersal between landmasses over geological timescales, and the ‘intrinsic’ ecological characteristics of clades that facilitate speciation and reduce extinction. Recent work on extrinsic processes in tropical forests has emphasised dispersal among landmasses against a backdrop of climatic fluctuations and tectonic activity for understanding patterns of diversity. However, the intrinsic characteristics of clades, including traits such as generation times and range size, are also important for determining diversification rates of specific lineages.

These two kinds of explanation for the origin of patterns of diversity are typically considered in isolation because studies have either focussed on individual clades where ecological variation is small, or on a range of clades with greater ecological variation but similar biogeographical history to identify specific mechanisms underpinning diversification. However, only by combining these approaches and considering patterns of diversification among clades that encompass a range of ecological characteristics and biogeographical settings can we obtain a complete understanding of the origin of the diversity of tropical forests.

Specifically, this project will test (1) whether variation among lineages in intrinsic, ecological traits is more important than biogeographical history in driving diversification in the tropical flora, and (2) whether the same intrinsic traits are associated with patterns of diversification in all biogeographical regions.