- Book information
- Where Do Camels Belong? The story and science of invasive species by Ken Thompson
- Published by: Profile Books
- Price: £10.99
Introduced species generally get a bad press – but not all alien invaders are villains, says Ken Thompson in Where Do Camels Belong?
WE HAVE all heard a lot of bad stuff about introduced species: they run rampant through our ecosystems, costing billions to control each year. They are also accused of driving native species extinct. Indeed, alien species are often cited as one of the big threats to biodiversity.
Purple loosestrife, for example, is often viewed as one of the worst invasive weeds in North America because it forms dense stands of tall, conspicuous flowering heads. But when ecologists looked closer, reports Thompson, there was little evidence of actual harm. Even in Hawaii – poster child for the noxious effects of alien species – invaders tend to make ecosystems more diverse, not less.
Nor are introduced species the financial burden they are often made out to be. For one thing, says Thompson, hardly anyone bothers to count the economic benefits of "aliens" such as wheat and cows – a sum that runs to $800 billion per year in the US alone. Moreover, much of the cost of the invaders turns out to be the money spent controlling them.
There's a deeper problem, too, in our attitude towards aliens. Viewed over millions of years, plants and animals are constantly shifting their distributions over Earth. Just a few thousand years ago, North America was full of camels. Indeed, they evolved there and reached their greatest diversity on that continent. So should camels be regarded as native or alien there today?
Then there is the small-flowered tongue orchid, native to mainland Europe, that first turned up in England in 1989. No one knows whether it arrived by seeds that blew across the English Channel – in which case it's an endangered native, worthy of nurture – or arrived stuck to someone's trouser cuff, in which case, says Thompson, "it's just another bloody weed, to be ruthlessly exterminated". Should how it arrived in the country really make that much difference?
Thompson makes his case in a lively, readable style, spiced with a healthy dose of sarcasm towards "aliens = bad" fundamentalists. Better yet, he bolsters his argument with plenty of citations from the scientific literature, which adds welcome heft.
Not everyone will find his argument convincing, however. When Thompson published similar arguments in scientific journals, sceptical opponents accused him of cherry-picking examples that fit his argument, while ignoring contrary evidence.
Even if there is any substance to that claim, Thompson makes a worthwhile point. Species aren't necessarily ecologically harmful just because they are introduced, nor are native species necessarily good for biodiversity: "If bracken were alien [to the UK], it would be seen as no less than a national emergency," he writes.
Instead, Thompson argues, we need to take a more conciliatory attitude and treat each species on its merits. We should still take care to avoid moving species to new places, and fight hard to control those aliens that are truly nasty, such as Australia's cane toads. But we may as well get used to the rest of today's aliens, and let them and their ecosystems settle down to comfortable coexistence. After all, he notes, many are doing that already, just as they have done throughout history.
This article appeared in print under the headline "Learning to love aliens"
Bob Holmes is a consultant for New Scientist
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