TOP 10 INTRODUCTIONS OF NEW SPECIES THAT WENT WRONG

Top 10 Introductions That Went Wrong
By Susan Nasr, Science Channel.

Ecological webs are so complex that it's hard to predict what will happen when we add a new species into the mix. There's no easy math. Nevertheless, we humans tend to think we know what the outcomes of such an action will be and think we can give it a try. After all, we're a relatively intelligent species, and we perch at the top of the food chain.

In this list, you'll see 10 cases in which yes, we meant to introduce a particular animal or plant species to a new environment, but no, we definitely didn't intend the consequences, like irreversible ecosystem collapses, extinctions or profusions of pests. We'll start with one that sings in the dead of night.

10. Blackbird

Blackbirds are native to Europe. They were released into New York City between 1890 and 1891, supposedly in an effort to introduce all of the birds of Shakespeare into the United States. From 100 original birds, the flocks grew to epic sizes, ranging from a few thousand to - in one instance - almost a million that descended on Springfield, Missouri, in 1977.

Their nuisance comes from their numbers. When 3,000 of them try to sit on a telephone wire, it collapses. When the birds fly around the Midwest grazing on cattle feed, they eat enough to hurt dairy cows' milk production and cost the farmer significantly in replacement grain. When poisoned, they die in huge numbers. In Missouri, when a few farmers poisoned grain in an attempt to get rid of the blackbirds, thousands of carcasses fell from tree branches and landed around the city. So did the droppings.

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9. Kudzu Vine

A hearty vine sat amongst the gladiolas and orange trees at the 1876 Centennial Exhibition, the first big World's Fair in the U.S. The exhibit was some North Americans' first look at kudzu [see Invasive species], an Asian plant. Either guests or sellers liked the vine because shortly after, it started to be sold. Great for gardens. Perfect for shading porches. But kudzu soon diversified and was promoted for use on farms. In the early 1900s, farmers used it as high-protein animal feed. In the 1930s, the U.S. government thought kudzu a remedy for erosion, paid landowners to plant it and sent the Civilian Conservation Corps to establish it in parks.

As farmers and families moved to cities, the land was left to whatever grew the fastest. That was kudzu. It can grow up to 7.5 inches (19 centimetres) in a day. According to the southern joke, you plant kudzu by throwing it down and running. It now represents one of the worst weeds in North America. Growing unchecked from a backyard garden, it will climb over a house. From the edge of a field, it will carpet an orchard or smother a forest. And of course, if you cut it, it will grow back.

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8. Brown Tree Snake

When the brown tree snake [see Invasive species] came to Guam, so did a nightmare. The snakes arrived by accident, on a cargo ship from the southern Pacific Ocean. Officials didn't know what would happen, so they let the snakes roam, hoping they would eat the island's rats. Some snakes also leaked into the pet trade. But the snakes wanted birds. Guam's birds, never having seen predatory snakes, weren't afraid. The snakes feasted, extinguishing 10 species of birds in a short time. They're now finishing the remaining two.

The ecological cascade gets worse. Since birds are scarce, trees that need birds to spread their seeds are disappearing, and spiders are surging. Brown tree snakes now outnumber people on Guam, up to 3,000 in a square mile. They run up an annual tab of several million dollars in power outages, as they climb utility poles to eat birds.

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7. Rabbit

The Romans domesticated wild rabbits by the first century B.C., penning babies to raise them for food. After Rome collapsed, rabbit farming survived, especially in Normandy, France, where the rich and the holy farmed them in little stone enclosures. When the Normans conquered Britain, they brought rabbits. The British and other Europeans raised them for food and fur in the 1100s and beyond.

Once farmers started planting vegetables, which happened at an untimely moment - when the rabbits' natural predators declined - it was unclear who was in control. Wild and domestic rabbits boomed, and they couldn't be kept out of the salad bar. Three of them eat as much as a sheep does, according to author David Taylor. They made a dent in agriculture by the 1800s. [See also: Rabbits in Australia.]

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6. Water Hyacinth

While they're pretty and purple, water hyacinths [see Invasiveness as an exotic plant] are weeds - prolific weeds that can double their population in 12 days, according to the Invasive Species Specialist Group. They originated in western Brazil but now grow almost worldwide. In most places, gardeners and pet owners imported the hyacinths for their ponds and aquariums then accidentally seeded them in wild bodies of freshwater by dumping plant waste into creeks.

China had a special introduction, farming the plant to feed to livestock. Given the right conditions, water hyacinth form shore-to-shore mats - in China and elsewhere. These plants pose a huge nuisance to processes that move water. They clog irrigation systems and drainage canals, causing flooding, and shut down hydroelectric power plants. They also block water travel, which in places like Papua New Guinea, where the water is the road, stops life. By lowering the amount of light and oxygen in the water, they transform water ecosystems, choking out fish and other plants and eventually turning open water into marshes.

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5. Nutria

Originally from South America, nutria or coypu [see Commercial and environmental issues and Herbivory damage to wetlands] look like little beavers. Fur farmers imported them to North America, Europe, Asia and Africa. But these little vegetarians escaped, or fur farmers released them. They slipped into lakes and marshes, where they munch the tender shoots, water lilies and reeds. In fact, enough nutria can mow a marsh until it becomes a lake. By pulling the grass, they rob animals of their hiding and mating places, including an endangered dragonfly in Japan. Their marsh mowing also has hurt many species of birds and fish. For people, the nuisance stemmed from the flooding that happened when marshes were no longer there to soak up water. On land, nutria have become great crop destroyers, ravaging Italian rice farms, sugarcane and sugarbeet fields, as well as alfalfa patches.

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4. Bush Currant

Bush currant (Miconia calvescens) is a tree grows in check in its native range of Central and South America, but it's a disease in other parts of the tropics. Hawaiians call it the purple plague, and Tahitians dub it green cancer. Both Hawaii and Polynesia imported the shrub for gardens, likely charmed by its green and purple leaves. Once there, its seeds spread to the rainforest through bird droppings, hikers and tire treads. When forest gaps opened from clear-cutting, fire, overgrazing or hurricanes, bush currant invaded the rainforest. It didn't just mix in; it took over.

Bush currant uses sunlight better than other rainforest trees, and it grows fast. The tree shades out any seedlings that try to colonize the gap. Once it forms dense stands, it prevents water from soaking into the ground; Oahu, Hawaii, may pay as much as $137 million per year because of groundwater loss. The shallow roots also encourage erosion and landslides, so if the invaded patch is on a slope, it eventually falls off the hillside. At that point, the land isn't even suited to agriculture, since erosion strips nutrients. Bush currant threatens about half of the native plants on Tahiti with extinction.

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3. Indian Mongoose

About the size of a squirrel, this rodent [see also Small Asian mongoose] was content to scamper through the Middle East and Asia. It has since become a problem on islands, from Puerto Rico to Hawaii. Why islands? Islands commonly have ship rats that eat local crops. When sugarcane farmers on these islands had enough of rats, they introduced mongooses as predators. But the mongooses didn't want rats. They wanted local birds and reptiles, especially species that laid eggs on the ground. Their appetite for threatened and endangered species has driven a bird, the Fijian bar-winged rail, and a snake, the Hispaniola racer, to extinction. In fact, name an island, and the mongoose is likely eating the eggs of a threatened species there, from the pink pigeons on Mauritius to the Garman's ground lizards on Grenada. And the rats are still eating the sugarcane.

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2. Mute Swan

Mute Swans [see Behaviour] are lovely, but they hog resources and exclude other birds. In the 19th and 20th centuries, Americans and Canadians imported these natives of Europe and Asia to decorate zoos and parks. After being let out or flying away, the birds landed in lakes, ponds and wetlands. Swans proved to be bad neighbours. Extremely territorial, they claimed entire lakes, driving off and killing other birds that encroached. They'll even attack children who get too close. After claiming a body of water, they overgraze underwater plants, further excluding other birds. In winter, they eat the roots of plants meant to sprout in the spring, again robbing other birds of food. They've gorged enough to drive water plants locally extinct. It's not only birds and plants that suffer; swans change the water community enough to threaten the fish.

1. Cane Toad

Introduce an animal to control a pest and get a worse pest. It's a theme running through our list that certainly applies to cane toads. Cane toads are native to Mexico, Central America and South America, where they hide in wet areas of the forest. When introduced throughout the world, cane toads were intended to be a farmer's friend. They eat insects, and farmers released them to attack beetles in fields of sugarcane, banana and other crops. Now cane toads are hopping around Egypt, Hawaii and more. As toads do, they've found wet places to live: drain pipes, which they clog, and drinking water tanks, which they foul. They sit under houses and belt out their mating call, which sounds like a telephone dial tone.

As predators, they're little poison bombs. When a death adder, one of the world's most poisonous snakes, swallows a cane toad, the death adder dies. Certainly if pet dogs and cats eat the toad, they're in danger. The toad can also squirt its toxic secretions several feet, so to kill a pet, the animal needs only to paw. The toad has helped to poison Guam's monitor lizards into decline, and it kills way more than its fair share of extremely deadly snakes in Australia. To make matters worse, Australia's environment favours toads that can hop far, which means the cane toad continues to spread.

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[Source: Science Channel. Edited. Links added.]