Competition among plants for resources such as water and light generally results in a size distribution in which there are some large plants and many small, suppressed plants. It is well known that growing plants at higher densities increases the magnitude of competition. From this, one would expect that traits that confer competitive ability would be increasingly favored as density increases. The principal investigators suggest that this may not be true at very high densities. Under extreme competition, growth of all plants is very suppressed, resulting in smaller differences between large and small plants. Consequently, traits that confer competitive ability may not be increasingly favored beyond some intermediate to high density. The investigators propose to determine the relationship between plant density and the favorability of traits that increase competitive ability by growing plants across a wide range of densities and comparing the performance of individuals with different traits. They will also measure the same relationship in a field population to determine if natural densities reach the threshold necessary for decoupling density and the favorability of traits that confer competitive ability. Competition is recognized as a widespread, important ecological force. Almost all agricultural plants, as well as those grown in natural environments, are strongly suppressed by competition. This work will permit an assessment of the role of density as a force shaping the evolution of traits that affect competitive ability in a natural environment. Results will also be of use to agriculturalists, particularly in determining the correct density at which to breed plants for enhanced competitive ability.
