Waterweed Invasions

Populations of plants and animals ordinarily migrate and multiply slowly over time as a result of the natural interplay among many ecological factors: soils, waters, glaciation, drought, the rise and fall of competitor species. Yet in some regions human activities have quickened the pace of change by dramatically altering the range and abundance of many species. Today plants and animals are shipped, sometimes accidentally, all over the globe to zoos and botanical gardens and for commercial and agricultural purposes. A small minority of the “alien,” or introduced, species become ecological as well as economic disasters; although they may have been innocuous in their native region, these species are transformed into aggressive pests or weeds that invade and dominate their new environment.