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How Invasive Species Work


Prevention and Eradication of Invasive Species
Steve Tyscko holds a carp in Havana, Illinois, on March 11, 2011. Asian carp have spread from retention ponds in the southern U.S. to the Mississippi River to the Missouri and Illinois rivers to the Great Lakes.
Steve Tyscko holds a carp in Havana, Illinois, on March 11, 2011. Asian carp have spread from retention ponds in the southern U.S. to the Mississippi River to the Missouri and Illinois rivers to the Great Lakes.
© John Gress/Corbis

In the 1970s, fish farmers in the southern United States imported Asian carp to clean up the mess left by their catfish. One day, the carp made a break for it and escaped into the Mississippi River. In the 21st century, the Asian carp swims in the waters of at least 23 states, destroying the biodiversity in many bodies of water. How do you kill the fish? The U.S. Geological Survey has developed a poison. Some fishermen, however, go Rambo on them, shooting the fish with arrows as they jump out of the water. Others, however, are catching the carp and eating them. They say it tastes similar to tilapia [source: Kraft].

Dealing with the Asian carp reflects the problems humans face when trying to control or eradicate an invasive species. You would think killing these pests would be an easy thing, considering that when a nonnative species enters a new ecosystem, only about 10 percent of the population will survive. Of those survivors, another 10 become pests [source: CISR]. That is, not all foreign species new to an area will become invasive. What's the problem?

At first, all infestation is localized. In fact, it's so local that humans don't even know its occurring. Eventually, the species breeds and gradually moves into other areas. However, the climate has to be right, and conditions have to be perfect for an invasive species to take over an area. That means the area has to lack natural enemies, including parasites, predators or pathogens. Some species, such as aphids, spread more easily than others because a male is not required for fertilization. By the time humans figure out an invasive species has taken over the area, it's much too late to do anything about it [source: CISR].

We can try, can't we? Of course. There are two main ways of controlling an invasive species. The first is something researchers call proactive management. That means excluding species by passing laws banning certain animals, plants, food and other products from coming into a country. Officials can catch many invasive species by stepping up border inspections. Proactive management also means destroying an invasive population during the early stages of infestation. In California, environmental officials successfully beat back an invasive weed that occurs naturally in tropical waters. When state officials spotted the plant, they shrouded it with tarpaulins and poured chlorine on top, killing the weed before it had a chance to spread [source: CISR].

The second way to control invasive species is through reactive management. That could mean doing nothing, or it could mean controlling the invaders by limiting their capacity to reproduce. This might mean planting crops that are resistant to a plant disease. It could also mean planting during a time of the year when a pest is not around. We could also use chemicals to kill the pests or introduce a natural predator, such as a parasite or pathogen, into the ecosystem [source: CISR].

What can you and I do? For one thing, go around your house and try to find any plants that don't belong there. Generally speaking, you can tell which plants are invasive if they crowd out the native vegetation. You can also go to this U.S. Department of Agriculture website and print out identification sheets. And please, don't flush baby alligators down the toilet or let a python wiggle out of the bedroom window. Grow only plants native to your area, and try not to move soil or wood great distances. We can keep our boats and fishing equipment clean, and notify custom officials anytime we travel overseas and decide to bring food, plants or animals into the country.

And please, no more kudzu or Eurasian watermilfoil.