Use of topographic ring model to identify candidate taxa for ring diversification around predicted barriers. A: The monotypic species Schreiber's green lizard Lacerta schreiberi, Iberian Peninsula (southern Europe). B: The polytypic species rosy boa Lichanura trivirgata, Baja California Peninsula. C: The polytypic species little shrike-thrush Colluricincla megarhyncha, island of New Guinea. D: Closely related lemur species from the genus Propithecus, Madagascar. In all maps, predicted barriers are shown by the black outline of grid cells, documented ranges of taxa are shown as gray polygons, and expansions or colonizations around the barriers are shown by the black arrows, as inferred from genetic evidence (see Additional files 6, 7, 8 and 9). Black scale bars at the bottom of each map correspond to 100 k.