Ecological opportunity and incumbency in the diversification of repeated continental colonizations by muroid rodents

Why some clades are more species-rich than others is a central question in macroevolution. Most hypotheses explaining exceptionally diverse clades involve the emergence of an ecological opportunity caused by a major biogeographic transition or evolution of a key innovation. The radiation of muroid rodents is an ideal model for testing theories of diversification rates in relation to biogeography and ecological opportunity because the group is exceptionally species-rich (comprising nearly one-third of all mammal species), it is ecologically diverse, and it has colonized every major landmass except New Zealand and Antarctica, thus providing multiple replicate radiations. We present an extension of the conventional ecological opportunity model to include a geographic incumbency effect, develop the largest muroid phylogeny to date, and use this phylogeny to test the new model. The nearly 300-species phylogeny based on four nuclear genes is robustly resolved throughout. Consistent with the f...