by Whit Gibbons

April 22, 2007

I asked University of Georgia research ecologist Dov Sax, who studies introduced species, how we should deal with the problem of exotic species that become problems. Here is his response.

"Alien species are here to stay! The United States would likely go bankrupt if we tried to control or eradicate every alien species in our country. Most people have heard of kudzu, house sparrows, and Argentine ants. These are just the tip of a very large iceberg. Thousands of alien species inhabit our land.

"Consider one little plant few people have heard of, the English plantain. This plant grows in urban lots, parks, along roadsides, on the edge of farms, and in mildly disturbed grasslands throughout the country. Several states list it as a noxious weed. Getting rid of this single species would not be easy. Imagine if we paid each American $100 to spend a day walking around pulling out each narrow leaf plantain that could be found. The cost would be 30 billion dollars. Unfortunately, in one day's time we could not find them all, especially since seeds of this plant lie dormant in the soil. If we had an annual `plantain day' for 10 years, we could come pretty close to eradicating this one little plant--at a total cost of $300 billion dollars. One plant down, 4,000 other alien plant species left to go-not to mention the introduced insects, fishes, birds, mammals, fungi, and microbes.

"We might try other ways to get rid of the narrow leaf plantain. We could introduce an insect from its native range in Europe that could damage the plant and beat back its large numbers, turning it from a common plant to a rare one. However, the several species of closely related native plantains might be threatened by an introduced insect. What about a designer pathogen such as a scientifically engineered virus to eradicate the plantain? This may sound like science fiction, but we could do this. However, it would be likely to leak out and infect other closely related plants. So what can we do? The answer is, not much, at least on a large scale.

"There are local solutions. In small areas, volunteers or paid workers can make a difference. Plants can be picked by hand, or sprayed with herbicides, or managed in other ways. Insects can be trapped, birds hunted, and fish caught. In small localized areas the aliens can be beaten back, but this is labor intensive and must be repeated over time, often on an annual basis. This may be considered desirable when trying to save a rare native species, attempting to preserve an area in a more natural state, or managing for a particular aesthetic appearance.

"Large-scale efforts can be effective in cases where the alien in question is relatively distinct from any native species. This permits biological control efforts to succeed, by reducing the risk of unwanted spillover effects on native species. Still, the number of real successes from biological control, particularly for widespread alien species, are relatively few while counterexamples of biocontrol projects that have gone awry are numerous.

"The best time to stop an invader is before it arrives. Prevention is the key to success. Unfortunately, new species arrive on a daily basis. A few countries, mostly island nations like New Zealand, enforce stringent importation regulations. The United States would benefit in many ways by following their lead, but it is unclear what the economic costs of such a policy would entail. Still, this is the only practical solution for stopping new invaders from causing problems.

"So, while we cannot possibly eradicate, manage, or control all, or even most, alien species, we can single out particular ones that appear to be an ecological or economic liability. Many of these can be managed in local or regional areas, and occasionally on a larger scale. Still we are best off if we avoid such management struggles in the first place. Alien species are a force of nature. Trying to control them can be as humbling as efforts to control an earthquake, tsunami, or hurricane."

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