Nutria today chomp their way through significant portions of public marshland in Chesapeake Bay. Starlings, introduced by homesick European colonists, compete with regional songbirds for food and nesting areas across the U.S. And zebra mussels, such effective filter feeders they can starve neighboring native clams to death, became known for their skill at plugging pipes. In the Pacific Northwest, invasive species include the nutria, the European green crab, and a plethora of plant invaders that choke out native vegetation and in some cases alter habitat. Ore. All of these invaders live in ecological balance in their native habitats. But lacking natural controls, their exploding populations can rupture the ecological balance of their new home, wiping out regional species in the process.
Many invasive species get a foothold due to human intervention, scientists say.
Some species are simply hitchhikers, tagging along with humans and our cargo as we hopscotch around the globe. Given the pressures on remaining ecosystems, some worry that invasive species may even alter the course of evolution. Eradicating invasive populations once they are established can be so difficult and damaging to native neighbors that every state in the nation has been asked to develop a formal method of preventing, identifying and stopping invasions before they take hold. President Clinton created a national Invasive Species Council last February to oversee that effort. Countries use trade policies to attempt to control the importation of diseases and unwanted species.