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Great Lakes Article:

Rapidly multiplying invasive species pose host of dangers to U.S.
By Rachel Ehrenberg
Knight Ridder Newpapers
12/19/03

Even in this age of heightened security, dangerous invaders continue to infiltrate the United States.

While they may appear harmless, they've got a rap sheet a mile long. Their infiltration threatens human health; it lays waste to fields, forests and waterways; and it costs the nation billions of dollars each year.

These foreign critters are what scientists call "invasive species," and they're the No. 2 cause of death to endangered species - beating out pollution, overharvesting, disease and global warming. They cause grave medical problems, damage crops, and can restrict trade.

"The situation is getting worse," said Daniel Simberloff of the University of Tennessee, Knoxville. "Invasive species have a plethora of effects on the environment. Some are so idiosyncratic there's no way to predict the things that could happen."

New research is untangling the convoluted interactions between invasive species and native plants and animals. And scientists are learning more about how to manage and eradicate non-native pests, whose numbers will continue to grow with increased international travel and trade.

An estimated 50,000 "exotic" plants, animals and microbes are already here, so the odds are good that some of these critters will be very, very bad, even though the risk that a single species will become invasive may be low, said John Chapman of Oregon State University.

"It's just like roulette, you spin the chambers and pull the trigger," Chapman said. "There's only one bullet in there, but who wants to play?"

Recent estimates suggest that a menagerie of foreign animals, plants and microbes costs the United States about $137 billion in damage each year. The figure takes into account the myriad ways invasive species hit the wallet, from the cost of herbicides used against foreign weeds to the cleanup of damage caused by feral hogs, said ecologist David Pimentel of Cornell University. And the number of invaders is likely to rise, he said.

"Globalization, the shipping of goods, more people, more people traveling and traveling rapidly, all of these factors increase the problem," said Pimentel, co-author and editor of a recent book on biological invasions.

A lack of public awareness also exacerbates the problem, Pimentel said. Without realizing the repercussions, people may take a liking to an exotic pest, inviting the organism to make itself comfortable in its new home. And many of these non-natives can be purchased easily. In the case of purple loosestrife, although more than 20 states have prohibited the sale of the invasive garden plant, it still can be bought at many nurseries.

While some nurseries encourage gardeners to use native plants, there are still many people who can't resist a flashy foreigner. "No one is ever happy with the species that they have," Simberloff lamented recently at a symposium in Knoxville sponsored by the Council for the Advancement of Science Writing.

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Of course not all "alien" species are harmful. In fact, most cultivated plants and many important domesticated animals - wheat, honeybees, cattle - aren't natives and they provide substantial benefits to the U.S. economy. What prompts concern is the occasional out-of-town critter that escapes human control and ends up decimating crops, or native plants, or people.

"West Nile has been extremely costly to the public, both in terms of illness and lives lost and in terms of mosquito control," said Dr. Norman Gratz, consultant to the World Health Organization and former head of its division of vector biology and control.

So how does a lowly worm or ratty thistle gain the ecological upper hand? When a pathogen's host is already here, as mosquitoes were with West Nile virus, it can tip the odds in favor of the invader, Simberloff said. But no two invasions are alike.

An organism may thrive because its natural enemies are absent in the new environment. It may have a biological edge over its native counterpart - many plants are adept at colonizing disturbed areas and quickly take over the fresh dirt at construction sites or roadsides. Other species may sit around innocuously for years and then something shifts, unleashing the Jekyll within.

In Florida for example, several species of fig tree are planted as ornamentals. Introduced in the 19th century, the figs were without their pollinating wasps and couldn't reproduce. But recently some of the wasps arrived and now at least two of the fig species have become invasive, and are gaining a foothold in Everglades National Park.

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The impact of a successful invader can ripple through an ecosystem in unpredictable ways, Simberloff said, and sometimes "invasional meltdown" occurs. Different non-native species can interact with each other, promulgating the spread of each.

For example, the zebra mussel, a poster child for invasive pests, is superior at filtering water. Clear water makes the Great Lakes a more inviting habitat for the aquatic weed Eurasian water milfoil. The milfoil changes the firmness of the lake bottom, helping the zebra mussel spread. Thus both species have become even bigger problems due to their interaction with each other.

The fallout from an invader establishing itself can be great - damage incurred by the zebra mussel is estimated to be $310 million - and many researchers urge aggressive eradication campaigns as soon as a potential pest is noticed.

Eradication has a bad name," Simberloff said, but this is mostly because of the notoriety of the failures. Like the $200 million spent in the 1980s to eliminate the fire ant from the southern United States. Without predators, these aggressive pests quickly spread and the pesticides and bait traps used against them often just wiped out their competition. After 11 years there were more fire ants than at the outset, leading some to call the campaign the "Vietnam of entomology."

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Certainly, the best-case scenario is acting on good information about an organism's biology. But a lack of knowledge should not be used as an excuse to delay action, Simberloff wrote in Conservation Biology earlier this year.

And a quick and dirty response may be crucial to preventing an invader from staking a claim. Nine days after the Caribbean black stripe mussel's presence was noted, the Australian government poured gallons of bleach and copper sulfate into the bay where the mussel had taken up residence. Everything was killed. But juveniles of various native marine species gradually came in from the open sea and repopulated the bay. The black stripe mussel hasn't been seen since.

"The bottom line on eradication is, it is important not to be too pessimistic about it, but to think carefully and act quickly," Simberloff said.

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Bringing in a pest's natural enemies, or "biocontrol," is often touted as a greener alternative to massive chemical eradication campaigns. And in some instances biocontrol agents do the job. But often they do the job too well, and not necessarily on the right species, Simberloff said.

The rosy wolf snail, a central Florida native, was introduced to several Pacific islands to control the invasive giant African snail. But the rosy wolf snail was too small to take on its intended prey, and proceeded to make its meals elsewhere. It is now blamed for more than 50 extinctions of native snails in Hawaii, Tahiti and other Pacific islands.

The possibility that a biocontrol agent would switch hosts, as the rosy wolf snail did, has been recognized for some time, said Dean Pearson, a research ecologist at the University of Montana. So scientists usually test an organism's palate before the creature is brought in as a weapon. Now scientists are looking beyond a creature's dietary preferences, toward the indirect ways biocontrol agents can affect an ecosystem.

"We are having a second revolution in biocontrol research," said Pearson, whose work focuses on the less obvious impacts of a mangy thistle relative, spotted knapweed. Two species of fly, introduced to eat the knapweed, may inadvertently increase the prevalence of the sometimes deadly Sin Nombre hantavirus, Pearson and a colleague reported recently in Trends in Ecology and Evolution.

Although predicting how a species will affect a community is difficult, "We can't afford to get rid of biocontrol," Pearson sid.

"Invasives are such a huge and growing problem, we need all the tools we can get," he said. "But we have to be really careful, this is Mother Nature we're messing with."

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The public is often oblivious to the damage that invasive species can cause, said Cornell University's Pimentel. A soft-hearted person might release a foreign fish into a pond or dump unused bait into a waterway without killing it. In fact, many species believed to have arrived in the ballast water of ships may actually have come into the country as live seafood, said Oregon State's Chapman.

Chapman, an invertebrate zoologist, just completed a survey of the clams, mussels and oysters that are available for sale in fishing markets in the western United States. Twenty-four of the 37 bivalves are non-natives, and 11 of these have already established self-sustaining populations in the Pacific Northwest, Chapman and his colleagues reported recently in the journal Conservation Biology.

"There should be warnings on packaging, `Live seafood, do not throw into nature,' " Chapman said.

So why aren't there ads to educate the public about the effects of invasive species? A campaign like "your brain on drugs" but aimed toward the dangers of invasives could be very effective, Pimentel said. (Imagine: "This is your pond. This is your pond under water hyacinth.")

But the agencies charged with managing non-native pests are poorly funded and organized, and without adequate resources for tackling invaders, education won't do much good.

"We are dealing with such a complex problem and even the federal agencies who are supposed to know really lack the information," Pimentel said.

Increasingly, scientists are championing "ecosystem management" as a way of handling non-native pests. The approach focuses on maintaining the health of an entire community, and while more research is needed, it is a promising strategy, Simberloff said.

But the success of any approach will depend on funding and public support. The western regional panel for invasive species had a budget of $40,000 last year, Chapman said, who is a member of the panel. "That's for every state west of the Mississippi," Chapman said. "What can we do with that? It's really just a drop in the bucket."

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