Australia's most unwelcome guest
It seemed like a good idea at the time. In 1935, two types of beetles were chewing through Queensland's sugar-cane fields. In desperation, growers turned to cane toads to battle the insects. They'd heard glowing reports about the warty, fist-sized amphibians from growers at a conference in the Caribbean two years earlier, and successfully lobbied to import them.Skip to next paragraph
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Australia would come to rue that day.
Instead of concentrating on beetles, the voracious toads began munching on almost everything in site: insects, bird eggs, and even pet food. Their poison killed predators - even pets - who tried to eat them. And instead of staying put in cane fields, they began to spread along a broad swath of the country.
In recent years, the cane toad has become a poster child for the problem of invasive species here, forcing the government to embark on a multimillion-dollar campaign to stop them.
Invasives are a major problem worldwide. Plants, animals, and even pathogens arrive in a new ecosystem, often wreaking environmental and economic damage in their newfound homes. The World Conservation Union (WCU) lists the planet's 100 worst invasive species, but that's just the tip of the iceberg.
In Australia, the problem is magnified. The continent is biologically rich, hosting a broad range of species found nowhere else on the planet. Australia is one of the world's top 12 "megadiverse" countries, according to the Australian Academy of Science. The other 11 are too poor to implement comprehensive long-term conservation programs.
Yet with a population of only 20 million people, the biggest current threats to native species in many areas are bush fires and invasive species, notes Kent Wommack, program director for the Nature Conservancy's projects in Australia.
Cane toads - a.k.a. giant toads, marine toads, or more formally, Bufo marinus - have the dubious distinction of joining the Caribbean tree frog and the bullfrog as the only amphibians on the WCU's list of worst invasive species. They have spread from the northeast corner of New South Wales to the tropical rain forests of the Northern Territory. They've invaded the ecologically sensitive Kakadu National Park and now are hopping toward the outskirts of Darwin.
If the projected effects of climate change hold true for Australia's part of the globe, specialists expect the toads to reach far into West Australia and, in the east, as far south as Sydney within the next 20 years.
Introducing them "was not an inspired idea," says Ross Alford, professor of biology at James Cook University here in Townsville.
The toads' successful invasion is all the more intriguing, he says, because they are so poorly adapted to the country's climate. They lose enormous amounts of body moisture to evaporation during the dry season; many die of dehydration. Many others starve when they've exhausted the food supply around dry-season water holes. Those food-free regions can extend for more than 100 yards from the water hole.
"But they breed like crazy and are toxic," he adds. "Those cover up a lot of faults in other areas."
Ironically, the toads are not viewed as vile interlopers in some of the areas they've reached outside their native northern Venezuela and Guyana. Florida has put up with them for years. Indeed, one gardening company's website holds that they should be destroyed only if they threaten young children who mishandle them or pets. Otherwise, the site counsels, the toads make great garden companions because they eat an enormous number of insects.
"No one in Florida seems to care," says Professor Alford, who attended the University of Florida and received his master's degree there. "People figure the state is so full of introduced species that one more or less doesn't make any difference."
Indeed, complacency is one of the big hurdles facing international efforts to stem the flow of invasive species, according to Faith Campbell, the North American representative to the Invasive Species Specialists Group, which compiled the 100-worst list for the WCU.
Education is another. Many people, she says, don't sufficiently appreciate the importance of biodiversity in ecosystems. And they don't know enough about their natural surroundings to realize what's out of place. By the time an alien species has encroached sufficiently to attract wide attention, it's too late.
"Outside of Australia and New Zealand, no one takes this stuff seriously," she says. Except for Hawaii, which is struggling to save its native species from mainland invaders, "in the US, it's generally not seen as a major issue."
Australia and New Zealand have been more successful building public support for control measures partly because they've stressed the threat to agriculture, notes Richard Mack, an ecologist at Washington State University.