Fig. 1

The axes of evolutionary radiation. Clades can show (a) strong phenotypic and ecological disparity like Anolis lizards or Hawaiian honeycreepers. Some clades (b) exhibit low morphological disparity despite of they have a wide variety of ecotypes (e.g., Plethodon salamanders) whereas others (c) present considerable phenotypic disparity, but little ecological disparity (e.g. African lake cichlids) suggesting a prominent role of sexual selection (disruptive or diversifying) as driving force in the speciation process. Clades (d) with limited morphological diversification and low ecological disparity (e.g., Acridid grasshoppers, Bythinella spring snails or Muroid rodents) constitute the most extreme cases along these axes and therefore, they have been frequently regarded as non-adaptive radiations