Environmental Engineering Reference
In-Depth Information
not proving as bad as once feared. The beasts of the outback started getting the measure of the toxic new-
comer. “The vast majority of smaller predators rapidly learned not to eat the toxic toads,” says Shine.
And slowly the bigger predators got the message too. Freshwater crocs learned to nibble the toads' back
legs and leave the rest. The black kite and a crow have both developed the trick of avoiding the poison
gland by attacking its belly or throat. “Aversion learning,” Shine calls it.
Evolution also seems to be working to defeat the new menace. Some snake species have developed
tolerance to the toxin. Researchers found that within a few generations, blacksnakes from toad-colonized
areas had developed smaller heads, since small-headed snakes can only eat smaller, less-toxic toads.
After initial declines as the cane toads advanced, there are revivals among monitor lizards, crocodiles,
and other species, including a local cat-sized marsupial called a quoll. Kakadu is not lost. “Our predic-
tions were dramatically in error,” Shine reported in 2011. “No native species have gone extinct.” Birds
and rodents turn out to tolerate the toxin.
33
Even humans are adapting. In Queensland, cane toads have
become part of the culture. Initially it was open season, with cane toad golf especially popular. But the
gutsy newcomer is now rather admired. The National Trust of Queensland considered it for a list of state
icons, cane toad purses and other souvenirs are rife, the state rugby league team is known as the Cane
Toads, and outsiders have even taken to calling Queenslanders “cane toads.” But it has been a long haul.
It would be foolish to claim that alien species never do any harm or that efforts to uproot them are always
doomed to fail. Neither is true. And advances in techniques may improve the chances of success, espe-
cially for biocontrols, where the main trick is to ensure the biocontrol won't start eating its way through
native species. But we need a sense of proportion, and too often the species police forget that. From
Macquarie to South Africa, a misplaced belief that ecosystems can be brought back to equilibrium by
removing one presumed felon has created new mayhem.
Take an area of the Florida Everglades known locally as the Hole-in-the-Donut. This area of farm-
land was established in the early twentieth century across twenty-five thousand acres of slightly elev-
ated ground at the heart of the Everglades. The new farms were seen as the prototypes for a large-scale
drainage of the Everglades being pursued by the governor at the time. But ideas changed. Once seen
as a putrid marsh full of dangerous creatures and disease, the Everglades was gradually rebranded as a
biodiverse wetland worthy of protection.
In 1947, the undrained area—the donut surrounding the hole—was turned into the Everglades Na-
tional Park. Later, park authorities decided to pursue their conservation mission by filling the hole in
their donut. In the 1970s they bought out the farmers and waited for marsh vegetation to reclaim the
abandoned fields. But the plowed, drained, and heavily fertilized soils were now very unlike the rest of
the park, and the nature that showed up mostly comprised nonnative species, like the Brazilian pepper
tree. “Every weed in South Florida found it to be a great place to grow,” says Jack Ewel, a restoration
biologist who worked in Florida for many years but is now at the University of North Carolina.
34
That alien invasion was not in the script. Nor was the fact that the thick alien undergrowth swiftly
became a haven for much local wildlife. Among those that liked it and dropped by with increasing fre-
quency were the last hundred or so of the Florida panthers, an endangered local subspecies of cougar
(
Puma concolor coryi
). Fleeing traffic and tourism in the more picturesque parts of the park, the cat
recently named the official state animal found the overgrown farms in the Hole-in-the-Donut an ideal
refuge. Its numbers began to rise.
Search WWH ::
Custom Search