The niche-filling process predicted by the "ecological opportunity" (EO) model is an often-invoked mechanism for generating exceptional diversity in island colonizers. Whether the same process governs lineage accumulation and trait disparity during continental colonization events is less clear. Here, we test this prediction by investigating the rate dynamics and trait evolution of one of Africa's most widespread amphibian colonizers, the true toads (Bufonidae). By reconstructing the most complete molecular phylogeny of African Bufonidae to date, we find that the diversification of lineages in Africa best conforms to a constant rate model throughout time and across subclades, with little support for EO. Evolutionary rates of life-history traits have similarly been constant over time. However, an analysis of generalists and specialists showed a shift toward higher speciation rates associated with habitat specialization. The overall lack of EO signal can be interpreted in a number of ways and we propose several explanations. Firstly, methodological issues might preclude the detection of EO. Secondly, colonizers might not experience true EO conditions and due to the size, ecological heterogeneity and age of landmasses, the diversification processes might be more complex. Thirdly, lower speciation rates of habitat generalists may have affected overall proliferation of lineages.

Biodiversity and Conservation Biology Department University of the Western Cape Bellville 7535 South Africa

Cameroon Herpetology Conservation Biology Foundation P O Box 8218 Yaoundé Cameroon

Department of Environmental Science University of Basel 4056 Basel Switzerland

Department of Life Sciences University of Roehampton London SW15 4JD United Kingdom

Ecology Evolution and Developmental Group Department of Wetland Ecology Estación Biológica de Doñana 41092 Sevilla Spain

Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum Friedrich Schiller Universität Jena 07743 Jena Germany

Institute of Vertebrate Biology Czech Academy of Sciences Brno Czech Republic

Museum für Naturkunde Berlin Leibniz Institute for Evolution and Biodiversity Science 10115 Berlin Germany

Natural History Museum of Geneva Department of Herpetology and Ichthyology C P 6434 1211 Geneva 6 Switzerland

Tropical Biodiversity Section MUSE Museo delle Scienze Trento 38123 Italy

References provided by Crossref.org

Terrestrial reproduction as an adaptation to steep terrain in African toads