Tuesday, September 27, 2016

Matt Ridley: Invasion of the alien species

In July, the New Zealand government announced its intention to eradicate all rats, stoats and possums from the entire country by 2050 to save native birds such as the kiwi. It’s an ambitious plan, perhaps impossible to pull off with the methods available today, but it’s a stark reminder that invasive alien species today constitute perhaps the greatest extinction threat to animal populations world-wide.

Birdlife International, a charity that works to save endangered birds, reckons that of the 140 bird species confirmed to have gone extinct since 1500, invasive alien species were a factor in the demise of at least 71—an impact greater than hunting, logging, agriculture, fire or climate change.

Rats, cats and diseases were the biggest culprits, contributing to the extinction of 41, 34 and 16 species, respectively. Most of these were on islands. The dodo on Mauritius, emblematic of extinction, was wiped out less by hungry sailors than by the rats, pigs, dogs and cats they brought with them. Hawaii once had 55 species of honeycreeper; today just 17 remain, thanks largely to rats and avian malaria, transmitted by alien mosquitoes brought by people. Guam has lost nine species of bird to an introduced snake.

But continents aren’t immune to invasion by alien species. In the Mississippi River, it is Asian carp; in the Everglades, Burmese pythons; in the Great Lakes, Russian zebra mussels; in the South, Indochinese kudzu vine. In Australia, cane toads from South America; in Lake Victoria in Africa, water hyacinth from the Amazon; in Germany, Chinese mitten crabs; in the Caribbean, lionfish from the Pacific. A fungus spread by African clawed toads (used in laboratories) has wiped out frogs in Central America.

On my farm in Northern England, three native species of animal are being extinguished by alien invaders from North America: the white-clawed crayfish by the signal crayfish; the water vole by the mink; and the red squirrel by the gray squirrel. Himalayan balsam flowers and Japanese knotweed infest the woods.

Aliens turn into pests away from home because they encounter naive and ill-equipped competitors or prey, and they leave behind their diseases and predators. Globalization is increasing the flow. An insect that would have struggled to survive a long journey by ship can stow away on board a plane. Today only Australia and New Zealand, whose isolated fauna and flora are especially vulnerable to invasives, take biosecurity really seriously.

European countries, by contrast, are lax in allowing exotic pets. In Britain, pet raccoons (native to North America) and raccoon dogs (native to China) have escaped into the wild and may one day establish breeding populations that would devastate native wildlife.

A paper published last month by a team of ecologists, led by Regan Early of the University of Exeter in Britain, points out that whereas most invasive alien species (IAS) have affected rich countries so far, the developing world is increasingly at risk: “Many of the global biodiversity hot spots that are highly vulnerable to invasion are found in countries that our results suggest have little capacity to respond to IAS (in particular Central America, Africa, Central Asia and Indochina).”

None of this is to say that invasive species are always a threat. They can bring positive effects, too, by increasing biodiversity within a region. Ascension Island in the Atlantic was once a barren volcanic rock, but is now much greener thanks to a deliberate policy, suggested by Charles Darwin, of bringing in plants from elsewhere in the tropics to create a forest ecosystem. Dov Sax of Brown University points out that New Zealand once had approximately 2,000 native plant species, has gained approximately 2,000 nonnative species that now have self-sustaining populations, and yet has lost fewer than 10 native plant species.

Another positive effect is that invasive species sometimes improve, rather than harm, ecosystem services—the quality of water, soil or air. Zebra mussels were so effective in filtering the water of Lake Erie that they made its water clear. In the American Southwest, the endangered willow flycatcher has taken to nesting on alien tamarisk bushes, embarrassing conservationists who spent millions trying to eradicate the plant for the sake of the bird.

The best way to fight invasive aliens is often with other aliens: Go back to their native country, find an insect or fungus that eats them, and bring it in to help. Early horror stories when alien predators introduced to control alien prey turned on native wildlife instead—cane toads in Australia, stoats in New Zealand—have given way to much more cautious and careful scientific introductions of highly specific control organisms. Done right, such biological control is indispensable.

The Centre for Agriculture and Biosciences International is an international agency that scours the native homes of invasive alien pests for predators that can control them. It found a rust fungus that has reduced the infestation of rubbervine weed from Madagascar in Queensland, Australia—by up to 90% in some areas. The Centre used two parasitic wasps to control the mango mealybug from Asia, which did huge damage to mango trees in Benin in Africa.

Vaccines that cause sterility are another promising weapon. Spreading food coated with such a vaccine could render a species sterile, causing its numbers to fall. This approach is working well in the lab with pigs—invasive species in various places—and may soon help to fight gray squirrels in Britain.

Genomics is the latest weapon. The Aedes mosquito that spreads dengue and zika in the Americas is an invasive alien, from Africa. A biotech firm called Oxitec has devised a way of suppressing its population using mass releases of genetically modified males (males don’t bite), which father offspring that cannot mature. In trials in Brazil, this method has achieved more than 90% suppression of numbers.

The next step is even craftier. Using a mechanism called “gene drive,” it is possible in the laboratory to create a genetic variant that will gradually infect an entire population of a species with infertility. Whether such a technique would work in the wild, and how it could be safely controlled, or reversed if it began to affect the species back in its native range, are still unanswered questions.

Many nonnative species are here to stay, and many are welcome additions to biodiversity of a country. But scientists are going to be very busy over the next few decades working to reverse the damage done by some and to prevent the arrival of others.

Matt Ridley, a member of the British House of Lords, is an acclaimed author who blogs at This article was first published in the Wall Street Journal.


paul scott said...

Freedom from intelligence
The Predator free by 2050 slogan was an introduced distraction to help reduce the pestilence on the invading housing an immigration crisis.
It worked for a few days but the persistent reality of the pest immigration and housing perception are not gone away one tiny little bit.
This slogan at a time when the Conservation department is reeling under reduced staff necessity.
A problem having no opposition is that the blue rinse Government can say and do what it likes.
Maggie Barry went on a awareness raising walkabout to schools where the children believed some of this stuff, about waving the magic wand and opossums dropping out of trees.
I don’t really know anybody Government with a broad range of understanding of genetic variation, species recovery and mutation and evolution in general.
Certainly not Nathan Guy, or Maggie Barry.

Matt Ridley on the subject of pest control by alien and genetic intrusion is his usual tidy scientific self. The rest of his colleagues in the house of Lords, as stupid as Bob Geldof on Sunday are still crying and threatening over Brexit and the evil climate warming, while Ridley gets on with things.
He is being gracious here is not describing the New Zealand pest free slogan as utterly ludicrous, as it is.
Instead he describes the future possibility of genetic modification as away to tackle each species pest one by one basis.
This does not guarantee success, even at a single specific level, there is always a bigger pest waiting around the corner to fill the niche of the one you have just taking out.

I expect more of these propaganda feel good slogan dreams to pop out at convenient times until the election next year.
The Predator free New Zealand slogan will drop out of memory as it is replaced by other blue rinse advertorial campaigns.

Clunking Fist said...

Ironic that in NZ, it is the Labour and Green parties that question immigration. What a bunch of racists, eh?

paul scott said...

Clunky. The post is about pest eradication in New Zealand. This is New Zealand Clunky,
On immigration here, you are lost, and not doing so well where live either.