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Exotic invasive species aggressively disrupting delicate U.S. ecosystems

September 2nd, 2009

By Melissa Segrest
Green Right Now

They started out as pets, perhaps living in little boys’ bedrooms, being shown off to friends and wrapping around arms. But then the Burmese pythons grew, and grew, and grew (about 7 feet in a year), and they weren’t so cute or easy to deal with any more.

So, trying to do the right thing, their owners gently released them into the wild, near the large, shallow “river of grass” that flows through much of south Florida, known as the Everglades.

Problem solved.

Not quite. Those pet pythons grew — up to 20 feet long and 250 pounds –and they eat anything from deer to bobcats to wood storks to endangered species. Less than a decade ago, there were only a few in the Everglades. Today, more than 100,000 of them are slithering around south Florida, crushing what was an already delicate ecosystem.

Even though the state is aggressively trying to find them and restrict the sale of them as pets, the python hunters will never catch up. And the giant reptiles are spreading, south into the Florida Keys and north into Central Florida. One estimate predicts they will eventually inhabit about one-third of the United States.

And that’s not taking global warming into account.

If there’s any wisp of a silver lining to this mess, it’s that the python problem has turned the nation’s attention toward the depth and scope of invasive exotic animals, fish, reptiles and plants.

The U.S. spends hundreds of millions of dollars every year to try and staunch the flow of invasive species. But the damage the invaders cause brings that total to about $35 billion annually, according to National Invasive Species Council. Worldwide, the economic toll from invasives tops $1.4 trillion, according to the Nature Conservancy, which publishes a list of ways people can help reduce that number.

The invaders tend to spread rapidly, eating or killing the food and habitats of native species. They can clog streams and rivers, alter entire ecosystems and potentially wipe out endangered species. They can cause major forest fires, destroy rangeland and even decrease tourism.

It’s hard to put a number on them in the US: The Fish and Wildlife Department estimates as many as 50,000 non-natives are here now, but of those, about 4,300 are trouble-making invasives.

“I can tell you that for the Nature Conservancy, wherever we work, globally and nationally, invasive species have been identified as one of the greatest threats to biodiversity,” said Doria Gordon, the Director of Conservation Science for Florida’s chapter of the Nature Conservancy.

Though relatively few imports become invasive, when they do, they can become a monumental problem, she said. Florida is a state where climate, population and ports create an ideal environment for voracious invasives. Reptiles such as monitor lizards, Cuban tree frogs and iguanas are growing quickly and gobbling up native species. “The Cuban frogs are capable of eating most of our native tree frogs,” she said.

The animals and reptiles may be more interesting, but it is the plants that really wreak havoc on the environment. They take over because, as exotics, they lack natural pests in their new territory. (Just as invading wildlife is able to run amok because their natural predators live on another continent.)

“Hydrilla and water hyacinth have been problems for years,” she said. “They constrain navigation and water flow, create hazards to navigation and power generation,” she said.

But Gordon reserves special scorn for a plant that poses perhaps the biggest threat to Florida’s native areas: Old World climbing fern.

Calling it a fern is misleading – it’s more like ivy on steroids. Native to Africa and Asia, Old World found its way into a nursery decades ago. Now, it covers large swaths of Florida’s uninhabited land, rapidly moving north thanks to wind-blown spores. Old World blankets the ground, bushes and even the top of forests, smothering everything it covers – like a leafy version of The Blob.

How can such a pervasive plant be controlled? “We try to contain them. At the edges, where densities are low, we can keep knocking them backwards,” Gordon said. Right now the northern boundary of Old World climbing fern’s range is near Orlando. “We’re now starting to look for spores in the air there,” she added.

“The real effort is to find a biological agent that can control the vine,” Gordon said, rather than using huge quantities of pesticides. Finding a living thing to battle back another living thing has only worked for a few species. “It’s difficult to find one that will only attack that specific species and not anything else.”

Hawaii is a perfect example of such well-intentioned plans gone wrong.

First Polynesians, then Europeans, arrived to the islands with their dogs, pigs, lizards, plants, cattle and sheep. The Westerners, unfortunately, brought along rats, too. The rats ate sugar cane and the unique flightless birds of the islands. To kill the rats, the mongoose was brought in. Unfortunately, the mongoose ate the birds, not the rats. Rats are nocturnal and the mongoose is not. Thus, dozens of the dwindling species of rare birds in Hawaii were wiped out.

Today, Hawaii’s struggle with non-native plants, animals and reptiles is worse than any other state, according to the U.S. Geological Survey.

Unleashing one exotic to battle another has happened on the mainland as well, according to Richard Mack, professor in the school of biological sciences at Washington State University. “Ironically, most of our problems we brought upon ourselves. Two-thirds of the plant invaders were deliberately introduced (via horticulture), and it backfired,” he said.

“The problem is that we don’t have a good handle on this. The funds, resources, they haven’t been allocated.”

There’s a cycle to it all, Mack said. “One of these invaders arises and causes havoc. There’s a call to deal with it and it takes a sustained effort and incredible persistence to get rid of one of these species.

“There may be initial success – the population numbers go down. That’s mistakenly taken as a sign that public funds can be pulled back. But these are living organisms, so they go back and build up their populations and it gets as bad as it was before,” he said.

Thus, money to combat the invasives dries up, and often the task of trying to control the pests falls on area communities.

One of the bad actors in the U.S. now, Mack said, is cheatgrass. It came from Eurasia about 200 years ago. “It’s had a devastating effect in the far west,” he said. Despite its size, it is a strong competitor with native plant species and is a factor in major forest fires in California or Nevada. “It also causes downstream siltation and erosion in the river systems in the west,” Mack said.

And who can forget what has come to be known as the “Vietnam of entomology,” the fire ant fiasco in the Southwest?

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