Alien species are taking over nature. Rogue rats, predatory jellyfish, wild boar, Japanese knotweed – all are headed for an ecosystem near you. These biological adventurers are travelling the world in ever greater numbers, hitchhiking in our hand luggage, hidden in cargo holds and stuck to the bottom of ships.  

Our modern, human-dominated world of globalised trade is giving foot-loose species many more chances to cruise the planet and set up home in distant lands.  Some run riot, massacring local species, trashing their new habitats and spreading diseases.  

Environmental campaigners in March claimed the invaders cost the British economy alone £2 billion a year.

Foreign species

We all like a simple story with good guys and bad guys.  So the threat of alien species invading fragile environments and causing ecological mayhem instantly gets our attention.  Conservationists have for half a century been in the forefront of the battle to hold back the alien tide. 

Me too.  As an environment journalist, I have written my share of stories about the carnage they can cause.  

Some of it is true. But do we fear the invaders too much?  Do the grey squirrels, American signal crayfish, Himalayan balsam and the rest do as much damage as is claimed?  And what about the thousands of other visitors that fit in without trouble?  Himalayan balsam is now vital for honeybees, and rhododendrons for nightingales.  

Who now remembers that rabbits were brought to Britain to be farmed? Or the fears of ecological meltdown that followed the arrival of the American muskrat in Europe a century ago.

Is our fear of newly-arrived foreign species a kind of green xenophobia? Most of us don’t treat foreign humans as intrinsically dangerous. Yet the orthodoxy in conservation is to stigmatise foreign species in just that way. Native is good, and alien is bad.

Often hilarious

I believe it is time for a rethink — time to consider whether aliens can sometimes be the good guys, and whether nature’s go-getters are sometimes actually rebooting ecosystems damaged by human activity.

While researching my book The New Wild: Why Invasive Species Will Be Nature’s Salvation, I found numerous places where biodiversity is increasing, and nature is recovering, thanks to aliens. And many more where interlopers that were once regarded as arch environmental villains are now quite at home and causing no lasting harm. Just like most human migrants.

I also found that many of the scary numbers attached to the economic cost of alien species are, to say the least, far-fetched. Yes, of course the damage caused by crop or tree pests can be huge. But what about Japanese knotweed?

The new report from the Wildlife and Countryside Link puts its cost to Britain at over £200 million a year. But nobody actually spends anything like such sums. The figure turns out to be an extrapolation to the entire country of theoretical eradication costs in Swansea, a uniquely infested city.

Global estimates of the damage from alien species are often hilarious. They assume, for instance, that every time a domestic cat kills a bird the bill is $30. This is the economics of the madhouse. And ecologists who should know better are party to it.

Transient and accidental

But this is about bad ecology as well as bad economics.  There is a dogma about aliens that lurks in our often outdated and ill-founded ideas about how ecosystems work.

We often think of rainforests, wetlands and other ecosystems as pristine and perfected biological machines in which every species has evolved to occupy a unique niche. So, the theory goes, losing a native species or gaining a disruptive alien can only be bad, and could be disastrous.

Conservation becomes a ceaseless task of keeping out the interlopers and maintaining nature’s presumed balance.

But fewer and fewer ecologists believe that this is how most of nature actually works. Yes, nature does have some amazing synergies. But they are the exception.

New ecological thinking holds that most ecosystems are much more random, transient and accidental.  They are constantly being remade by fire, flood, disease – and species are forever coming and going, adapting and evolving.

Damage to nature

In this new vision of nature, change is not the enemy of nature, but its essence. And ecosystems are neither fragile nor finely tuned.  They are temporary, versatile, resilient and adaptable. 

When invaded by foreign species, most ecosystems don’t collapse, and few natives go extinct.  Often, they prosper better than before, with the new arrivals forming new alliances with natives in evolving ecosystems.  Co-evolution is constant.

That is why North America has many more plant species than it did before Europeans showed up, and only a handful of native extinctions.  And why San Francisco Bay, America’s most invaded marine ecosystem, is healthy enough to have just got accepted by the Ramsar Convention as a wetland of international importance.

If, as most ecologists argue, more species is good for an ecosystem, making it more resilient against climate change or other threats, then most alien invasions deliver just that.  And there is surely no scientific basis for the common practice of ignoring alien species when biodiversity is being assessed.

None of this say conservation doesn’t matter.  On the contrary, the world’s ecosystems are in crisis.  Humans have done huge damage to nature, and in the 21st century we urgently need to turn that round.  But we will never do it by trying to recreate our vision of a pristine past.  We must give nature room to recolonise as it will.  To create a “new wild”.

And alien species will sometimes have a critical role in that.  Nature’s desperados, carpetbaggers, go-getters, innovators and colonists are often its best chance of rebounding from the havoc caused by our chainsaws and ploughs, our pollution and climate change.

They can be part of the solution rather than part of the problem.  True environmentalists, I believe, should be applauding the aliens.  The old wild is dead; but welcome to the new wild.

This Author

Fred Pearce will be speaking at The New Wild: Why Invasive Species Will Be Nature’s Salvation at Edinburgh International Science Festival at 6pm 12 April 2018. Find more information on the show and book tickets online. The New Wild by Fred Pearce is published by Icon Books, £8.99.