Rapid evolution of an invasive plant..pdf

261 Ecological Monographs, 74(2), 2004, pp. 261–280 q 2004 by the Ecological Society of America RAPID EVOLUTION OF AN INVASIVE PLANT JOHN L. MARON, 1,6 MONTSERRAT VILA?, 2 RICCARDO BOMMARCO, 3 SARAH ELMENDORF, 4 AND PAUL BEARDSLEY 5 1 Division of Biological Sciences, University of Montana, Missoula, Montana 59812 USA 2 Centre de Recerca Ecolo?gica i Aplicacions Forestals, Universitat Auto?noma de Barcelona, 08193 Bellaterra, Spain 3 Department of Ecology and Crop Production Science, Swedish University of Agricultural Sciences, Box 7043, SE-750 07 Uppsala, Sweden 4 Environmental Science and Policy Department, University of California, Davis, California 95616 USA 5 Department of Botany, University of Washington, Seattle, Washington 98195 USA Abstract. Exotic plants often face different conditions from those experienced where they are native. The general issue of how exotics respond to unfamiliar environments within their new range is not well understood. Phenotypic plasticity has historically been seen as the primary mechanism enabling exotics to colonize large, environmentally diverse areas. However, new work indicates that exotics can evolve quickly, suggesting that contemporary evolution may be more important in invasion ecology than previously appreciated. To determine the influence of contemporary evolution, phenotypic plasticity, and founder ef- fects in affecting phenotypic variation among introduced plants, we compared the size, fecundity, and leaf area of St. John’s wort (Hypericum perforatum) collected from native European and introduced western and central North American populations in common gardens in Washington, California, Spain, and Sweden. We also determined genetic rela- tionships among these plants by examining variation in amplified fragment length poly- morphism (AFLP) markers. There was substantial genetic variation among introduced populations and evidence for multiple introductions of H. perforatum into North America. Across common gardens in-