Much of the functional diversity of life is thought to have evolved in multiple bursts of adaptive radiation—periods of rapid speciation associated with diversification into a multitude of ecological niches (Simpson, 1953; Benton, 1995). Studying the causes and mechanisms of adaptive radiation is therefore expected to make important contributions to understanding the evolutionary underpinnings of biodiversity and its ecological structure. Distinguishing between effects of chance, historical contingency and ecological
determinism, as well as their interactions is of prime importance. Yet, this perhaps is the greatest challenge that investigators of adaptive radiations face when trying to make sense of events in the past. The full complexity of adaptive radiation has eluded analytical and computer-based modeling, although some new approach has recently emerged (Gavrilets and Vose, 2005). Instead, experimental work using the rapid evolution in microbial cultures has taken center stage. Studies of microbial systems have helped to confirm that stable and heterogeneous environments facilitate diversification, and that intraspecific competition in a resource-limited environment can produce negative frequency-dependent selection, which can act as an important driver of ecological diversification.