A central mystery in ecology concerns how some exotic plants that are rare in their native range attain staggeringly high densities where they have been introduced. This research examines this problem with a study of an introduced weed in western North America, houndstongue (Cynoglossum officinale), both in its introduced range in Montana and its native range in Germany. The research involves two components. First, through long-term demographic monitoring of plants in both ranges, the life stages (i.e. seeds, seedlings, adult plants) that most limit population growth of houndstongue in each range will be quantified. Second, parallel experiments in the native and introduced range will be used to explore the relative roles of three factors that may contribute to houndstongue's increased success in North America: increased disturbance and a greater response of the plant to this disturbance than in Europe; escape from specialist insect herbivores; and an ability to flower several times in the introduced range compared to only once in the native range.
While many hypotheses have been proposed to explain what allows exotic plants to dominate native plant communities, few rigorous experimental tests exist. This research will provide one of the few quantitative tests of these mechanisms. In addition, by identifying which life stages limit population growth, the work will also provide guidance to management efforts to control this noxious weed.
