Abstract
We investigate an individual-based model of adaptive radiation based on the biogeographical changes of the Great African Lakes where cichlid fishes radiated. In our model, the landscape consists of a mosaic of three habitat types which may or may not be separated by geographic barriers. We study the effect of the alternation between allopatry and sympatry called landscape dynamics. We show that landscape dynamics can generate a significantly higher diversity than allopatric or sympatric speciation alone. Diversification is mainly due to the joint action of allopatric, ecological divergence, and of disruptive selection increasing assortative mating and allowing for the coexistence in sympatry of species following reinforcement or character displacement. Landscape dynamics possibly increase diversity at each landscape change. The characteristics of the radiation depend on the speed of landscape dynamics and of the number of geographically isolated regions at steady state. Under fast dynamics of a landscape with many fragments, the model predicts a high diversity, possibly subject to the temporary collapse of all species into a hybrid swarm. When fast landscape dynamics induce the recurrent fusion of several sites, diversity is moderate but very stable over time. Under slow landscape dynamics, diversification proceeds similarly, although at a slower pace.