The global transportation of goods has a long history. As we have moved around the planet so we have transported with us many different plants and animals, introducing them to new regions. Some have been taken unwittingly, stowing away on ships, in timber or in foodstuffs; others have been deliberately introduced to remind us of home.
Within the UK we have seen countless examples where introduced species have gone on to become a problem within the wider countryside; American mink, signal crayfish and Japanese knotweed all spring to mind. There are, however, many instances where an introduced species has simply filled a vacant niche and established itself without having any impact on other species. One of the most interesting aspects of the debate about these introduced species has been the extent to which something is considered native or introduced. Some of the creatures that were deliberately introduced many centuries ago are considered as natives, while recent colonists arriving unaided are sometimes treated as unwelcome invaders.
Our own perceptions of particular species cloud the debate and we even see conservation practitioners arguing with each other about whether or not a species should be controlled. The ruddy duck privides a good example. This species was introduced to Britain by the Wildfowl and Wetlands Trust in the 1950s, when individuals escaped from Slimbridge. An expanding population saw individuals move into Europe, where they came into contact with the related white-headed duck, a globally-threatened species. The solution seemed simple enough, cull the ruddy ducks to save the white-headed duck, but there was stiff opposition from many quarters, including from birdwatchers who liked seeing these birds here in Britain. The West Midlands Bird Club, for which the ruddy duck was a special species, even managed to smuggle a subtle image of the species into their new logo once the ducks profile switched to that of unwanted alien.
For other species the problem comes from uncertainty over whether it is native or not. Our slowly expanding eagle owl population almost certainly stems from aviary escapes and deliberate releases. There is, however, a very small possibility that an Eagle Owl from elsewhere in Europe might reach our shores. This uncertainty is used by some as an argument against culling the pairs breeding here now, even though some bird carry the jesses that reveal their captive origins. You might wonder if it really matters; you might even argue that it is better to accept that our activities will result in introductions and that conservation money is better spent elsewhere. Perhaps the most pragmatic solution would be to remove definitely introduced species as soon as they appear, accepting that other species may be too well established now to manage effectively.