Understanding why there are so many species is an essential question in biology that continues to generate considerable curiosity and drive evolutionary research. Moreover, people seek to understand how species that are closely related can reside in very different niches and co-occur in areas. Darwin observed such an adaptive radiation with finches in the Galapagos, where the species of birds differ in the size and shape of their beaks, allowing them to specialize on particular food sources, thus reducing competition between the species. African rift lakes such as Lake Tanganyika and Lake Malawi also contain spectacular examples of adaptive radiations with cichlids. These fish not only have brilliant colorations, but they have diverged to specialize on particular food sources, such as fish eggs or the eyes of other fish.
While there are increasingly many examples of adaptive radiations that have occurred, we don’t necessarily know why they occur in the first place and to which clades. Is it when there is sufficient ecological opportunity, through pathways described by Simpson (1953) such as colonization, new resource availability, species extinctions, or novel resource utilization through trait evolution, or will radiations happen despite the lack of opportunities, as Losos summarizes in which a clade can supplant another clade through competition or it could radiate and form a new ecological opportunity that did not previously exist (Losos 2010)? Recently, Gómez and Buckling have explored the role of ecological niche availability in the experimental diversification of a strain of Pseudomonas flourescens bacteria. In soil microcosms, they test the diversification of this species in the presence and absence of a resident community and with or without a bacteriophage. They found that the bacteria experienced adaptive morphological diversification in the absence of a resident community, but not in the presence and that phages did not impact diversification. Selection was stronger in the absence of the community, as well. Moreover, the new morphotypes were capable of utilizing more variation in substrates, which would be consistent with greater radiation to utilize unoccupied niches, but remains a constraint when the niches are already filled.
I think it is excellent that the authors consider how the community context that a species is establishing in may influence the evolutionary trajectory of a species or clade following that establishment. While they recognize the resident community is difficult to completely recreate in the lab, their paper is built upon a series of simple and elegant experimental designs with clear predictions and very interesting results that support field observations in other systems and can serve to help inform future studies exploring the context which adaptive radiations occur in. While “nothing in biology makes sense, except in the light of evolution” (Dobzhansky 1973) it is important to also consider that “nothing in evolutionary biology makes sense, except in the light of ecology” (Grant and Grant 2008).