The Effects of Competition and Ecological Opportunity on Adaptation and Diversification

Abstract

Ecological processes have the potential to influence evolution through their effects on selection. This thesis explores the effects of two ecological factors - competition and ecological opportunity. Intraspecific (within-species) competition is often expected to drive adaptation and diversification by increasing selection for the use of novel resources, thereby alleviating the detrimental effects of competition. However, this is not always the expected outcome; theory suggests that intraspecific competition can also drive convergent evolution. On the other hand, interspecific (between-species) competition is usually expected to impede adaptation and diversification because competitor species occupy potential available niches, preventing the focal species from diversifying to do so. In this thesis, I review previous experimental studies exploring the effects of competition on adaptive diversification, and then directly test these effects using experimental evolution of the bacterium Pseudomonas fluorescens. I confirm that intraspecific competition drives adaptive diversification, while the effects of interspecific competition are varied. Strong interspecific competition impedes adaptation and diversification, while the presence of weak, non-diversifying interspecific competitors drives diversification through increased resource competition. The presence of ecological opportunity is essential for adaptation and diversification, and so variation in attributes of those opportunities is expected to have important effects on the dynamics of adaptive evolution. In another evolution experiment with P. fluorescens, I tested the effects of variation in ecological opportunity on adaptive evolution and found that the type and arrangement of ecological opportunities drives adaptation but, in this system, not diversification. I also show that ecological opportunity drives differences in the degree of parallel evolution at the phenotypic and genotypic level. Finally, I explore some unexpected genetic changes identified in one of these evolved populations - two synonymous mutations that conferred fitness benefits, and show that the observed fitness improvements are the result of increased gene expression. I have shown that ecological processes can play an important role in shaping the evolutionary trajectories taken by populations. Understanding the interactions between ecological and evolutionary processes is vital for our understanding of evolutionary dynamics as a whole, and the studies laid out in this thesis represent valuable contributions to this field of study.