Species interactions in a changing environment: Elevated CO₂ alters the ecological and potential evolutionary consequences of competition

Question: How will global changes impact the ecological and evolutionary outcomes of competition? Hypothesis: Global changes that alter resource availability, such as rising atmospheric carbon dioxide (CO₂) concentrations, will alter the effects of competition on mean fitness and patterns of natural selection. Because species exhibit different growth responses to elevated CO₂ and because different traits may aid in competition against different taxa, these ecological and evolutionary effects may depend on the identity of the competitor. Organism: Arabidopsis thaliana grown under intraspecific competition or interspecific competition with the C3 grass Bromus inermis or the C4 grass Andropogon gerardii. Field site: BioCON (Biodiversity, CO₂, and Nitrogen) experiment at Cedar Creek Ecosystem Science Reserve, Minnesota, USA. Methods: Manipulate the presence and type of competition experienced by A. thaliana populations growing under ambient or elevated CO₂ conditions. Measure the interactive effects of CO ₂ and competition on mean fitness and on patterns of natural selection. Conclusions: Elevated CO₂ reduces the effects of competition on mean fitness, alters the relative fitness effects of different competition treatments, and minimizes the strength of competition as a selective agent.