Links between Island morphology and endemism

Most islands host an endemic biota, i.e., present nowhere else on Earth. This is the case, for instance, of Madagascar. It has been shown that different populations of lemurs, endemic to the island, are mostly distributed along the watersheds surrounding Madagascar, creating a so-called micro-endemism, while the populations living on the high-elevated watersheds, on the central plateau, are not showing this micro-endemism. Here we wish to address the question whether there exists a correlation between the evolution of the landforms (i.e., the geometry of the watersheds) of Madagascar and the hybrid evolution of lemur populations? More broadly, can the tectono-geomorphic evolution of an island be advantageous or disadvantageous to the flourishing of micro-biodiversity?

To answer these questions in a quantitative manner, we combined a Landscape Evolution Model based on the Stream Power Law and taking into account flexural isostasy, with a speciation model. We first developed a morphometric index to differentiate between islands with a central plateau surrounded by smaller basins, like Madagascar, from conical islands, like Sri Lanka. We then predicted patterns of biodiversity as a function of the index value and its time evolution. We show that for the tectono-geomorphic evolution to influence patterns of biodiversity requires a specific range of model parameter values, in particular the parameters characterising dispersal and mutation. We finally used phylogenetic observations to constrain some of these parameters.