REZNICK, David N.; GHALAMBOR, Cameron K.; Univ. of California, Riverside ; Colorado State: Selection in Nature: Experimental Manipulations of Natural Populations

Numerous studies have documented evolution by natural selection in natural populations,but few are genuine selection experiments that are designed and then executed in nature. We will focus on these few cases to illustrate what lessons they can teach us beyond what is learned from the more common laboratory studies that dominate this symposium; we will focus on the costs and benefits associated with field experiments. Both types of study allow us to evaluate cause and effect relationships because a planned experiment can be accompanied by a more direct evaluation of the factors that cause evolution. Field studies have the benefits of our being able to interpret the results as adaptations to specific features of the environment and being able to test evolutionary theory in a context in which all of the tradeoffs associated with a trait are realized; in the laboratory, organisms may be shielded from the fitness tradeoffs associated with the evolution of a trait. As part of the analysis of such tradeoffs, we can evaluate the extent to which the evolution of different aspects of the phenotype are integrated or potentially constrain one another by examining the correlation matrix among suites of traits. Field experiments carry the cost of our being more limited in the precise control of independent variables. A positive aspect of this cost is that it allows us to evaluate the extent to which causal selective agents interact with one another in a natural setting, rather than being limited to examining single factors in isolation. For example, manipulating predation alters mortality rates, but it also alters density and resource availability, which may either facilitate or oppose the evolution of particular traits. Finally, we can characterize the magnitude and rate of evolution by natural selection.