It is now evident that natural populations harbor far more genetic variation than was expected prior to initiation of electrophoretic studies 20 years ago. Theoretical work has clarified what processes may potentially be responsible for the maintenance of such vast stores of genetic variation, but there has been insufficient experimental work to demonstrate the actual mechanisms in more than a few unusual cases. The proposed studies will investigate the importance of a particular mechanism for maintaining genetic variation: the process of locally varying selection in conjunction with genetically based variation in environmental response. In particular, the magnitude and nature of genetic variation of individual plants in response to the density and composition of neighboring plants will be documented. These studies will permit prediction of the response to selection under differing biotic environments. Such predictions will be compared with observed responses in selection experiments. Because natural variation in the biotic environment is ubiquitous in wild populations, the findings of these studies may have bearing on the general importance of locally varying selection. The focal species for this work include one native and one introduced species. This system may therefore serve as a model for elucidating the evolution of interactions between species following invasions of exotics into wild communities and may provide insights into methods for enhancing the success of native communities following such introductions.
