Invasive species: Battling the enemy within

PARIS: Some aliens arrived as stowaways. Others were brought in deliberately, for fun or profit. And others were so tiny that nobody noticed them until way too late.
They became a nightmare. They killed and devoured natives, stole their homes, sickened them with pathogens.
Sci fi? No: the alien invasion is happening right now.
It could be occurring in your garden. In the forest where you like to feel in harmony with Nature. It is almost certainly unfolding on the farms which produce your food.
It’s the tale of species that mankind brings to new habitats where they spread uncontrollably, ousting endemic wildlife and becoming major pests. “Invasive species have a huge impact worldwide. In some countries, the cost is astronomical,” says Dave Richardson, director of the Center of Excellence for Invasion Biology at South Africa’s University of Stellenbosch.
The International Union for Conservation of Nature (IUCN), staging a conference in South Korea next month, says foreign encroachment is the third biggest source of species threat. Take the American grey squirrel — “a rat with good PR,” say enemies — which is displacing Britain’s scrawnier red squirrel. Or the Burmese python, gorging on small mammals in Florida’s Everglades.
Invasive species inflict more than $ 1.4 trillion (1.12 trillion euros) in damage each year, or five percent of global GDP, according to an estimate made 11 years ago.
“Those numbers are controversial because it’s difficult to put finite figures on these sorts of things,” said Tim Blackburn, director of the Institute of Zoology at the Zoological Society of London.
“But the impacts are pervasive and affect so many aspects of life. The cost has the potential to escalate as we take more species to more areas where they don’t naturally occur.” Many costs are indirect. For instance, US farmers use truckloads of pesticides to control foreign weeds, while in central Europe, their counterparts are surrendering tracts of land to the giant hogweed, a toxic Asian shrub.
There is the bill from the European rabbit, introduced for food by British settlers to Australia and New Zealand only to become cursed for ravaging grasslands and crops.
In the southern United States, Asian carp were imported in the 1970s to help clean up algae in commercial catfish ponds. Flooding washed the carp into the Mississippi River system, where they now threaten commercial and game fishing in the Great Lakes. Invasive species have followed man throughout his odyssey.
Polynesians wiped out innumerable bird species as they island-hopped across the Pacific over eight centuries, bringing in rats that had stowed away on their ocean-going canoes.
The trend accelerated in the early- to mid-19th century.