Alien Invasion

 

The aliens are here, living alongside us.  They will do anything to survive and we must be vigilant if we want to preserve life as we know it.  I’m not talking about slimy purple creatures from the planet Zob, I’m talking about plants and animals, alien to Britain, that threaten our countryside. So why are these aliens such a threat?

It’s a Worldwide War Zone

It is now generally accepted that the World hasn’t always been the way it is today.  The vast array of living things on Earth, together with the various and complex ecosystems they make up, have evolved gradually to reach their current levels of complexity.  The balance of nature is constantly shifting and changing as the result of an unending battle for supremacy in which every living thing is fighting for survival. 

Given the chance, frogs or even eggplants would dominate the world.  Happily, or unhappily – if you’re an eggplant, they can’t.  The spread of an organism is restricted by the availability of suitable environmental conditions, by physical barriers (such as mountains and oceans that it can’t cross) and by other organisms in its surroundings competing with and eating it.

The invaders are waiting

Environmental changes that alter conditions locally, or even globally, can often trigger major changes in ecosystems that allow new, colonising, organisms to invade and take over.  The living things that once dominated can find themselves less able to cope with the new conditions than the invaders and they are forced to either move on or are wiped out.

Here in Britain we have seen some pretty major changes through the ages as our little Island has drifted slowly North from the equator at a speed roughly equal to the rate at which your fingernails grow.  The fossils preserved deep underground in coal seams reveal that 240 million years ago most of Britain was covered by tropical swamp.  More recently, the last ice age, 15,000 years ago, covered the majority of the country in glaciers and forced everything south for a long winter.  When, nearly 10,000 years ago, things started to warm up again the plants, animals and other organisms we now think of as native to Britain moved in.  

The Human Factor

Before humans started travelling around the world, natural barriers effectively kept many ecosystems separate.  With the exception of migrant animals there was little opportunity for organisms to travel the world to find suitable new places to live.

When we started to spread across and colonise the Earth that all changed.  Wherever we went, we took domesticated plants and animals with us.

From the time our ancestors first arrived here from mainland Europe we have been deliberately importing and releasing animals to improve our food supply.  As society developed we imported animals to farm for profit, hunt for sport and, occasionally, because we wanted them for decoration. 

Many of these reintroductions failed as conditions weren’t suitable or the introduced organism couldn’t compete with the animals and plants already present.  Some succeeded because the alien fitted into a gap or niche in the ecosystem that it could exploit without causing too much hardship for the existing species and it became part of the food web.  Others wreaked havoc as the introduced animal or plant managed to out-compete a native species and, in the absence of the natural competition from the other organisms in its native ecosystem it spread out of control.

Part of the scenery 

The Romans didn’t just bring central heating and the habit of wearing sheets to Britain, they also imported Fallow Deer, Edible Dormice and, quite possibly Rabbits.  Rabbits were again imported in the 12th Century.  Today, there are now tens of millions of them, hopping around, grazing pastures and eating farmer’s crops.

Birds have also been introduced.  Common Pheasants, a familiar sight in the countryside, were imported for food in the twelfth century and soon spread nationwide.  These were followed, in the seventeenth century, by a host of birds imported principally to make the countryside ‘prettier’.  These included: Canada Geese, Reeves Pheasant, Lady Amherst’s Pheasant and the Red-Legged Partridge.

The habit of introducing species in an attempt to make Britain more ‘interesting’ reached its peak in Victorian times.  There was even a society, ‘The Acclimatisation Society’, whose stated aim was to introduce and hybridise exotic animals and plants from far off lands.  Many animals released during this period are, however, still with us.  The Edible Dormouse, the little Owl, Sika Deer, Reeve’s Muntjac (another kind of deer), Chinese Water Deer and, of course, the Grey Squirrel.

The deliberate release of alien organisms into the wild in Britain is now illegal.  However, another route used by aliens to invade, is still open. 

The infiltrators

Wherever humans have travelled, certain animals, most notably Black Rats, Brown Rats and House Mice have followed close behind.  Some pretty damaging alien invaders have managed to sneak in to the country this way, and continue to do so.  Today, with people and goods zipping around the earth by ship and plane more than ever before, the opportunities for biological hitchhikers are just becoming better and better.

If you go to a beach and look at the shells that have been washed up, you don’t have to search long before you find a Slipper Limpet.  On the South coast there are whole beaches almost entirely made up of their washed up shells.  Amazingly, they are an invader that sneaked into Britain when we attempted to import American Blue-Point Oysters in the 19th Century.  They were imported to help save the British or Edible Oyster from being wiped out through over fishing, or at least that was the plan.  However, the Slipper Limpets, which compete with the Oysters for space and another shellfish invader, the American Oyster Drill; which actually hunts Oysters, have only made the situation worse.

Some pretty large things have escaped into the countryside too.  In the 1920’s Muskrats from North America and Coypu, from South America were imported to be farmed for their fur.  They escaped and colonised local rivers causing damage by eating waterside vegetation, digging up riverbanks and causing floods.  With no predators to control their numbers, the only solution to the problem was to exterminate them.  Muskrats were eliminated by 1935 but the Coypu proved more difficult.  However, it was finally eradicated, as far as we know, in 1989.

The North American Mink, also imported for its fur has proved more troublesome.  The Mink was first recorded breeding in the wild in 1957, since then, it has spread throughout the country.  Mink are aggressive predators and have had a big impact on populations of ground nesting birds, small rodents (including the now rare Water Vole), fish and its competitors.  It is now so widespread that eradicating it is no longer an option.  However, the increased competition from Otters over recent years appears to be forcing it out of some areas.

Plants too have escaped into the wild.  One of the most famous is Rhododendron; popular with gamekeepers for the ground cover it provides and loved by gardeners for its beautiful flowers.  They had no difficulty escaping into the wild and are exceptionally good at taking over.  In addition to being evergreen and able to keep light away from low growing plants they are highly toxic so herbivores don’t munch them.  They produce millions of seeds, can re-grow from small fragments of root or shoot left in the ground and are resistant to all but the strongest weed killers.  In Wales where I live, whole mountainsides are now covered in them and the cost of removing them has been put at tens of millions of pounds.

The battle continues

Enthusiasts are still demanding exotic plants for their gardens and ponds.  Many of these are known to be fast-growing invasive species that have already caused harm to ecosystems both here and elsewhere.  In spit of this, the plants are sold without license or even a warning that their escape into the wild could cause great harm.  Exotic animals continue to enter Britain via the pet trade and are, once again, sold without warning.  Following the craze for owning red-eared terrapins around ten years ago, many were dumped by pet-owners in lakes and ponds where they have wreaked havoc.  None have bred here yet, it’s too cold for them, but they might manage it one day.

Ships continue to criss-cross the ocean, carrying biological hitchhikers attached to their hulls or in their ballast water.  In order to keep them floating at the right height when they are not carrying a full load of cargo ships take on water.  When they get to their destination, they dump it.  This has enabled the larvae and seedlings of a number of organisms to jump from one side of the world to the other.  Most never travel far from the port where they enter the country, however, others are becoming international pests, clogging waterways and invading ecosystems.

The International Union for the Conservation of Nature recently listed ‘species translocation’ as the second greatest threat to biodiversity on Earth after habitat loss.  Once again it seems we are ignoring the lessons of the past and storing up more problems for the future.  The aliens are moving in, and they’ll change the world forever if we let them.

 

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This article first appeared in SciTec magazine (2002).