As communities assemble, species may accumulate not only by immigration from outside the community, but also by in situ evolutionary diversification. Traditionally, immigration and diversification have been studied separately by either ecologists or evolutionary biologists, respectively. However, our recent experimental results indicate that these processes may be tightly linked, with small differences in immigration history greatly affecting the evolutionary emergence of diversity. This work incorporates immigration history into the burgeoning field of research on "eco-evolutionary dynamics," where ecological and evolutionary processes operate interactively.
Our study system on this subject has been experimental populations of the bacterium Pseudomonas fluorescens, which undergoes rapid adaptive radiation in the laboratory. Using this system, we have identified mechanisms by which subtle differences in early immigration history affect the extent of diversification. Specifically, these effects arise via niche pre-emption within functional groups and indirect facilitation among functional groups, both affecting the ability of new mutants to increase in number.
We are now examining the conditions under which the extent of diversification is particularly sensitive to immigration history. Our working hypothesis is that the importance of immigration history to diversification is determined by the degree of prior adaptation of founding populations to the new environment. Our results so far indicate that immigration history affects diversification more extensively when founding populations are less well adapted to the new habitat at the time of immigration. We are investigating the mechanistic basis of this effect.