PLANT OUTLIERS - AN ECOGENETIC PERSPECTIVE

Members of colonial plant species often occur as scattered individuals well beyond the borders of local populations. The ecological and genetical importance of these outliers to local populations and to the species as a whole have not been considered. A review of the reproductive biology of outliers and of sparse plants in general indicates that they produce fewer seeds per flower than plants within populations. Nevertheless, they successfully interbreed over large distances. I propose that outliers form large, diffuse assemblages of interbreeding plants that may fill the gaps between some local populations. These outlier assemblages may be prime sources of extraneous pollen and seeds, retard the divergence of local populations between which they reside, and form the nuclei for new populations. Outliers may receive more or less pest pressure than plants within populations. They serve as interpopulation bridges for pathogens and herbivores.