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Cat Macquarie, invasive species, introduction of species
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Macquarie Island’s Cat Removal Highlights Perils of Species Introduction

January 14, 2009 12:02 PM
by Josh Katz
The cat extinction program on the Australian island of Macquarie has backfired. It represents another case of invasive species introduction gone wild.

Cat Extinction Plan Wrecks Vegetation in Macquarie

The plan to remove all feral cats from Macquarie in order to help the native bird population has taken an unexpected toll on the island, located between Australia and Antarctica. The cats were apparently keeping the island’s rabbit population in check; without them, the rabbit population has skyrocketed and the rabbits have subsequently ravaged the vegetation that the birds need to live.

Researchers, led by Dana Bergstrom of the Australian Antarctic Division, revealed their findings in the Ecological Society’s Journal of Applied Ecology on Tuesday. They determined that the plan to remove the cats “caused environmental devastation” that will cost $16.2 million to fix, AP reports.

According to Bergstrom, “We estimate that nearly 40% of the whole island area had changed, with almost 20% having moderate to severe change” by 2007, reports Science Daily.

This is not the first time authorities have attempted animal population control on the island. The study indicated that seal hunters introduced rabbits to the island in 1878. Cats, introduced about 60 years earlier, began feeding on the rabbits. But, as the rabbits continued to destroy the island’s vegetation, “Myxomatosis and the European rabbit flea (which spreads the Myxoma virus) were introduced in 1968,” according to Science Daily.
The move thinned the rabbit population, which greatly helped the vegetation. But with fewer rabbits to feed on, the cats looked to the native birds as prey. Authorities then sought to eliminate the cats, and “Since the last cat was killed in 2000, Myxomatosis failed to keep rabbit numbers in check,” Science Daily writes, and once again, the birds are in dire straits.

The park service will now attempt to the rid the island of rabbits, rats and mice, hoping that taking them all out at once will allow the birds and their habitat to thrive. The new effort will be launched in 2010, and the park service “will use helicopters with global positioning systems to drop poisonous bait that targets all three pests. Later, teams will shoot, fumigate and trap the remaining rabbits,” according to AP.

Related Topics: The downside of invasive species

Cane Toads
The Australian cane toads are perhaps the most famous example of species introduction having unintended consequences. The cane toad predicament was even referred to in an episode of “The Simpsons.” In 1935, cane toads were brought from their native habitats in Central and South America to Queensland, Australia, to feed on the scarab beetles that were eating Australian sugar cane crops. Not only did the toads fail to reach the necessary height to catch the beetles, but the original 100 toads reproduced wildly and spread across the continent. Also, the cane toads were quite successful at feeding on everything else: “small mammals, other amphibians, snails, terrestrial and aquatic insects, and even dog and cat food,” according to conservation Web site Their toxic defenses and prolific breeding helped turn the cane toad experiment into a nightmare for Australia.

The most recent cane toad dilemma in Australia involves crocodiles. Freshwater crocodiles are devouring the cane toads as the amphibians spread to new habitats, but the crocs are dying from eating the poisonous toads. “[In 2006] we counted more than 600 crocodiles and in 2007 we counted less than 400,” Dr. Mike Letnic, of Sydney University said. “There were dead crocs everywhere. The only thing that had changed between visits was that cane toads had moved through the river system,” The Guardian reported in June 2008.
Fish Fight Malaria in Pools of Foreclosed Homes
In May 2008, findingDulcinea reported that Gambusia affinis—small, subtropical fish that eat mosquito larvae—were being used in California, Arizona, Florida and other areas dealing with the rising number of foreclosures in order to rid the homes’ swimming pools of potentially malaria-causing mosquitoes. But the Gambusia Control Homepage argued that introducing the “mosquito fish” could be potentially harmful to native fish populations and other invertebrate populations and can have an adverse effect on certain ecosystems.
Trout in Yellowstone
Yellowstone National Park has been trying to decrease the population of lake trout that were illegally placed in the lake in the 1980s. Since they were stocked, the lake trout have eaten native Yellowstone cutthroat trout, causing that population to fall steeply. According to The Billings Gazette, “Cutthroat are important to the Yellowstone ecosystem because they provide nutrition for an estimated 42 species of vertebrates, including predators like grizzly and black bears, eagles, osprey and otters.”
Himalayan Balsalm
In the April–June 2006 issue of Conservation Magazine, Robin Meadows examined efforts to remove Himalayan balsalm, considered “one of the top 20 invasive plants in the U.K.” The study revealed that “removing the balsam benefited other nonnative plants the most,” and some of the nonnative species that benefited were also invasive species. Therefore, “Although there have been calls for eradicating Himalayan balsam along U.K. riverbanks, the researchers urge caution,” according to the magazine.
Louisiana’s Trouble With Invasive Species
Tulane University provides several examples of species that have been introduced into Louisiana and the surrounding area with unfortunate repercussions. The Nutria, Red Fire Ant, Monk Parakeet, Water Hyacinth, Chinese Tallow, Eurasian Collared-Dove, and Cattle Egret are species that have taken a toll on the state’s ecosystem.

Reference: Unintended consequences


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