Since the Origin was first published, biologists have come to use the phrase ecological opportunity to describe the processes that can produce a diverse group of species from a single colonizing ancestor. Islands provide colonizing species with new food resources and an escape from predators and competitors. Under these highly favorable conditions, island species can live at much higher population densities than possible on the mainland—a phenomenon called density compensation. This increase in population size is often accompanied by increased variation among individuals, and greater competition from crowding neighbors creates strong benefits for individuals that try new ways to make a living.To learn how ecological opportunity really is all around us, you'll have to go check out the whole post.
Given enough time, one big, variable population will begin to fracture into smaller populations with different lifestyles. Given even more time, those smaller populations will stop interbreeding, and become different enough to call separate species. If that seems like a stretch of the imagination, consider that the processes of ecological opportunity are occurring all around us—as invasive species spread across the landscape, and viruses multiply in a new victim’s bloodstream.
Kudzu, taking advantage of ecological opportunity. Photo by Suzie T.
Yoder, J.B., S. Des Roches, J.M. Eastman, L. Gentry, W.K.W. Godsoe, T. Hagey, D. Jochimsen, B.P. Oswald, J. Robertson, B.A.J. Sarver, J.J. Schenk, S.F. Spear, & L.J. Harmon. (2010). Ecological opportunity and the origin of adaptive radiations. Journal of Evolutionary Biology, 23, 1581-96 DOI: 10.1111/j.1420-9101.2010.02029.x