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Alien invasion threatening native species

by Rowan Hooper

An invasion has been going on under our noses. It is multipronged, ruthless and very difficult to repel. It has been called an “ecological apocalypse.”

If you look out your window you may be able to see evidence of it. That pigeon flying past? An invader. Likewise, the cat by the garbage. Most are so familiar we don’t even think of them as invaders, but they are not native to Japan. There are many more, and most are far less obvious.

“Non-native invasive species have been popularly described as one of the four horsemen of the ecological apocalypse,” says Nisha Owen, a conservation biologist at the Zoological Society of London. “They are a real and pressing danger to biodiversity and ecosystems.”

Outside of my window in London I can see two ring-necked parakeets in a tree in my garden. Their bright-green plumage and raucous squawking call are not typical of the English garden — these birds are native to Africa and South Asia — but they live now in large numbers in southeastern England, and in the rest of Europe.

The parakeets of London nest early in the year and occupy holes in trees that native species such as woodpeckers would use. Pretty though they are, there are thousands in London alone and they are now classified as a pest.

In Japan, alien species are widespread and well-established. Some of the native species threatened by invaders are well-known. There is the Amami rabbit, an extremely unusual species of rabbit sometimes called a living fossil as it is so different from other species of rabbit and hare.

Carnivores that have been introduced by humans — sometimes deliberately, sometimes accidentally — now threaten the very existence of the Amami rabbit.

“The Amami rabbit is one of the most evolutionarily distinct and globally endangered mammals in the world,” says Owen, who works on the EDGE of Existence Program (www.edgeofexistence.org), which highlights and conserves evolutionarily distinct and globally endangered animals in the world.

“Although declared a Japanese national monument, this species is under threat from the introduced small Asian mongoose — one of the world’s most invasive species — which has killed large numbers of rabbits since their introduction in 1979 to control snakes,” she says.

OK, you might be thinking, but the establishment of parakeets in England and Asian mongooses in Japan is hardly enough to qualify as an “apocalyptic” invasion. Even if you add pigeons and cats, it’s not the end of the world.

However, there are many thousands more invasive species and, added together, you start to see the scale of the problem. For example, in Europe there are more than 13,000 non-European species that live in the wild.

There are hundreds of non-native insects, amphibians, reptiles, birds and mammals breeding regularly in Japan — so many that I couldn’t count them all in the database. For anyone interested, Dr. Koichi Goka of the Invasive Species Research Team at the National Institute for Environmental Studies in Tsukuba (my old research institute) has put together a great online resource in English: www.nies.go.jp/biodiversity/invasive/index_en.html.

Here are a few of the invaders Japanese biologists are most concerned about. They are classed as “100J” species, the list of Japan’s top 100 worst invasive pests.

In Wakayama and Aomori prefectures, Taiwanese macaques have established themselves. They hybridize with native Japanese macaques, so “contaminating” the gene pool of the native species. In Tokyo and Chiba Prefecture, there are populations of snapping turtles, released by people who purchased them as pets. These turtles attack and eat native freshwater animals.

There is a moth — the fall webworm — the caterpillars of which devastate native trees. There is even a cane toad. Notorious as one of the worst invasive species in Australia, there are cane toad populations on some Okinawa and Ogasawara islands.

The invasion situation is so bad that biologists are proposing a new way of tackling the problem: create a “Black List” of invasive species — the opposite of the Red List of endangered species that is collated by the International Union for the Conservation of Nature.

It’s not a simple problem to solve. Even if it was easy to catch or kill all the individuals in the wild of the species you were interested in, sometimes a species that is an invader to Japan may be rare elsewhere. This is best illustrated by an exotic and dramatic-looking species that has established itself in Kamogawa and part of the Katsuragawa river network in Kyoto, the Chinese giant salamander. You’ll know it if you see it — they are monsters, growing up to 1.8 meters long.

“The Chinese giant salamander (is) another evolutionarily distinct and globally endangered species that is desperately in need of conservation attention in China,” Owen says. “Unfortunately, this species happens to be a major problem in Japan, threatening the native Japanese giant salamander through competition and hybridization.”

The biologists proposing the creation of a Black List of invasive species say it can be used to prioritize species for action, as required by international policies on biological invasions.

The Convention on Biological Diversity was signed in Rio de Janeiro in 1992 and requires that “By 2020, invasive alien species and pathways are identified and prioritized, priority species are controlled or eradicated, and measures are in place to manage pathways to prevent their introduction and establishment.” The paper about the Black List is published in PLOS Biology.

Humans are, of course, the most dangerous of all species, and could easily be given the No. 1 spot on the Black List.

Many scientists are in agreement that the sheer impact of humans on the planet means we have initiated a new geological era: the Anthropocene — the age of human impact.

For more on this, I recommend “Adventures in the Anthropocene,” by Gaia Vince (published by Chatto and Windus), an epic, global account of our impact on the biosphere.

Rowan Hooper (@rowhoop on Twitter) is the news editor of New Scientist magazine. The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is “Hito wa Ima mo Shinka Shiteru (The Evolving Human).”