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Speaker:  Olivier Hardy, PhD, Universite Libre de Bruxelles

The phylogeographic structure refers to the way phylogenetically related species or populations are distributed across spatio-environmental gradients. These patterns are studied in the frameworks of community ecology (inter-specific level) and population genetics (intra-specific level) but usually using different data analysis tools. However, it is possible to use a common descriptive framework at the two levels and attempt a comparison. Here, Olivier will use examples from tropical African forests to illustrate how the phylogeographic structures can inform on population or community processes.

At the inter-specific level, from local to continental scales, phylogenetic turnover appears well correlated to the ecological distance between plant communities, independently of their geographical distance, while species turnover depends both of spatial and ecological distances. Species turnover and lineage turnover can therefore provide complementary information to decipher biogeographic isolation and ecological differentiation.

At the intra-specific level, the phylogeographic structures observed among populations of African tree species seem to result essentially from (past) biogeographic isolation, possibly driven by Quaternary climate changes (forest refuge hypothesis). However, these phylogeographic structures established early, sometimes during the Pliocene, and while they might have been reinforced during subsequent glacial–interglacial cycles, interglacial phases did not lead to genetic homogenization. Therefore, interpreting phylogeographical patterns of African trees must account for a much deeper past than previously assumed, and cannot be limited to the last glacial period, reflecting their slow population dynamics.

Olivier Hardy is based at the Université Libre de Bruxelles and leads a group conducting research in population genetics and community ecology, with a special interest for African tropical forests.