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Where Do Camels Belong?

The Story and Science of Invasive Species

Ken Thompson

(London Times)

The common-sense answer to Ken Thompson's question, 'where do camels belong' is 'in the Middle East'. Inevitably, it is wrong. Try North America, where the animal evolved some 40m years ago. Try South America, where the camel family is at its most diverse today - what with all those related alpacas and llamas. Try Australia: it is the only country, now, where wild camels are found.

The bigger point, behind the camels, and behind this polemical study of invasive species and what is and is not native, is that the very idea of animals and plants 'belonging' anywhere is fatuous. Yet that does not stop us spending millions conserving 'natives' and exterminating 'aliens'.

Thompson first helped make these arguments in a controversial article in the science journal Nature in 2011. He presents them here in a lively and punchy way. You walk away from this book feeling flushed and a bit bruised.

His starting point is that our understanding of what belongs where is just a single frame from a very long movie - one in which plants and species have been migrating, both with and without man's help, for millennia. The English oak? Spanish. Privet hedges? Japanese. Welsh leeks? Introduced by the Romans - along with apples, pears, garlic, onion, parsley, celery, cabbage, peas, lettuce, rosemary and thyme, not to mention chickens, rabbits and pheasants.

We are hopelessly irrational about what we choose to call native, and set arbitrary dates for when species qualify. In Britain, we choose to pause the film, broadly, at around the time of Jane Austen. In America, they make the cut at Columbus. But if an alien proves attractive or useful, we bend the rules. "If it's nice, it must be native," as Thompson puts it.

The curious case of the Scottish beavers reveals how confused our attitudes are. Hunted to extinction in the 17th century, beavers escaped from captivity and recolonised the river Tay some 12 years ago. Landowners again targeted them for extermination, even while conservationists were introducing another population of beavers, pronounced genetically closer to the extinct British natives, over in Argyll.

The Tay beavers were accused of depleting salmon stocks, even though there was precious little evidence. This, argues Thompson, is part of a pattern. Panicky headlines about 'invasions' and 'plagues', backed up by poorly conducted studies, obscure the fact that most foreign plants and animals do not reduce biodiversity. Nor do alien invasions cost us, asserts Thompson, the millions quoted by conservationists (eager for donor funds) and invasion biologists (seeking research grants). The '$100 - $200bn' sometimes quoted as the annual bill for the US economy of invasive aliens, for instance, accounts for every possible negative cost, right down to the impact of the influenza virus. It fails, though, to include anything on the positive side of the balance sheet.

Our stupidest error is to blame invaders for declines of native species. In doing so, we mistake correlation for causation. When American mink escaped British fur farms in the 1950s, for instance, they were blamed for the loss of native otters. Yet mink and otters eat different foods. And the otter is 10 times heavier than the maligned mink. What was really killing otters was pesticide pollution.

Intensive agriculture, and changing climate, is altering habitats on a global scale, and certain species are good at exploiting the new landscapes we are creating. 'We have the plants (and animals) we deserve,' observes Thompson, nicely.

Whether these 'anthropophile' species are natives or outsiders, he insists, has nothing to do with it. We simply tend to notice the bigger, uglier and newer species. Take the hysteria surrounding giant African snails. The sheer size of these brutes and the population explosion that occurs when they arrive in a new country (before an inevitable decline) make them a prime provoker of media panic. African snails are even supposed to spread a kind of meningitis. In response, conservationists have introduced a predator snail, Euglandina rosea. It has had little effect, alas, although it does turn out to transmit meningitis to humans much more effectively than the original African snail - making it 'exhibit A in any account of how not to run a biological control programme'.

Thompson is surprisingly keen on introduced predators, considering such history. For controlling British rabbit populations, he suggests the Iberian lynx and the Spanish imperial eagle. Conservationists would never 'play God' with a non-native species in the wild, he points out, yet British gardeners blithely import £1bn-worth of ornamental plants every year - and 10% of the imported species escapes. As he comments: 'We're playing God already.' Meanwhile, the Iberian lynx is dying out. 'Sometimes it seems many conservationists would prefer a species to go extinct,' Thompson spits, 'than to survive somewhere it doesn't 'belong'.'

Thompson's arguments are powerful and his examples are fascinating, but he presents only part of the picture. He makes a brave defence of the invasive zebra mussels, for instance, by pointing out that alongside clogging water-intake pipes, and costing the power industry billions, they also help filter water. But even he does not defend bona-fide baddies such as Japanese knotweed, which can grow a metre a month and destroy roads and foundations, or the brown tree snake, which is devouring its way through the Pacific island of Guam - or indeed cats or rats, or the grey squirrel, which is surely the definitive British invading alien, yet bafflingly is not mentioned at all.

And in his determination to blast our irrationality, Thompson pays too little heed to the importance of the irrational. Alien species may increase regional biodiversity overall, but people love and want to conserve the flowers and creatures they already know and associate with their homes. In short, plants and animals have cultural value as well as scientific; the camel really does 'belong' in the Middle East, if that is what we all want to believe. What is belonging but a shared emotional state?

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