Correlations Among Environmental Agents: Implications for Plant Ecology and Evolution

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9318523 Miller Studies on the ways in which natural selection leads to the evolution of species have demonstrated that many traits of interest, such as leaf shape or growth rate, are controlled by numerous loci (many genes), but that one can qualitatively predict how traits will evolve when undergoing natural selection. For example, previous research has investigated how herbivory by insects would lead to evolutionary changes in herbivore resistance of a plant species. Clearly, however, organisms are affected simultaneously by multiple environmental agents. The dune annual Sabatia stellaris, for example, appears to be simultaneously affected by resource competition, water availability, and herbivory. The proposed research asks how selection for one agent (e.g. competition) is affected by the simultaneous action of a second agent (e.g. herbivory). Theoretical predictions suggest that the selection by any one agent will be increased, in some cases dramatically, by the presence of any second agent%%% The proposed research will quantify selection for traits related to competition, herbivory, and water stress in Sabatia plants grown under a variety of different experimental conditions in the field: competition only, herbivory only, water stress only, and several combinations of these three environmental agents. In each environment, a number of plant traits known to be important for dealing with competition, herbivory, and/or water stress will be quantified. By counting the seeds produced by plants with these traits under various conditions, selection for these traits will be quantified in each environment and predictions can be tested. The results of this study may be important for understanding basic questions about rates of evolutionary change of species in different natural environments and the maintenance of genetic diversity. They may also be important for developing or understanding breeding programs in agricultural systems where factors su ch as completion and herbivory are commonplace.