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Villains, Victors and Victims: The Great Invasions of Britain

Firebird PR promotes special edition of UK wildlife review focusing on invasive species

Alien invaders are usually the subject of sci-fi or horror movies, but this year they are the focus of a special edition of the People's Trust for Endangered Species' assessment of the challenges facing Britain's wildlife. The State of Britain's Mammals report, written for the Trust by Professor David Macdonald and Dr Dawn Burnham from the University of Oxford, Department of Zoology's Wildlife Conservation Research Unit (WildCRU), provides an overview of research carried out by wildlife and conservation experts across the country and in this particular instalment, explores issues around invasive mammalian species and their impact on our native ecosystem.

Invasive animals are transported around the globe beyond their native range, either intentionally or accidentally through the movement of people and products. There are 14 invasive mammal species in Britain today, most of which were deliberately brought to the country through a combination of aesthetic, economic and scientific reasons. Some non-native mammals, such as rabbits and house mice, arrived in the UK about 1 000 years ago and have since integrated into the country's natural community. Other more recent arrivals are regarded as distinctly "unBritish", such as mink imported from North America to stock the British fur trade.

Although some invasive species arrived long ago, the report's authors suggest that the decision to consider a naturalised non-native species as an 'ecological' citizen hinges solely on the nature of the damage to our environment and native wildlife, whether economic or biological, and whether there is the possibility of remedial action. The ecological effects that invasive species have on native populations and landscapes vary from negligible to devastating. The report highlights five consequences of the arrival of non-native species to our shores:

Predation - interactions between invasive predators and their prey varies, but can threaten extinction such as the case of American mink which devastated the native water vole population, already under threat from loss of habitat. Globally, predation is the cause of about a third of the documented negative impacts of invasive mammals.
Competition - competition can be indirect ('exploitation competition') such as grey squirrels competing for seeds hidden by red squirrels, or direct ('interference competition') such as the struggle between American mink and the recovering otter population in the UK.
Disease - infectious diseases carried by invasives may be benign to their hosts, but have dire consequences when introduced to new communities. For example, the brown rat carries parasites and pathogens which can infect humans and livestock.
Hybridization - cross-breeding can occur between closely related species, such as indigenous red deer and sika deer, or Scottish wildcats and domestic cats.
Ecosystem - some invasions can affect entire ecosystems, such as rabbits whose grazing maintains chalky grassland, dune and heathland.

Factors such as globalisation and climate change mean that the threat of further mammal introductions to the UK and their potential long-term success remains high, though difficult to predict. Prevention of further invasions is desirable, providing a more cost-effective option than eradication, and some UK policy and legislation does aim to regulate and monitor invasive mammals and control schemes (e.g. The Wildlife and Countryside Act of 1981, Natural England's invasive non-native species framework strategy). Indeed in some instances, there are obligations to consider the re-introduction of some native species which have gone extinct, mostly due to the interaction of humankind, as in the case of beavers which were already rare in England by the 10th century and are now extinct in this country.

Jill Nelson, CEO of PTES highlights: "Our campaign to conserve Britain's native mammals is rooted in finding more about each animal's behaviour in response to the various threats they face and translating that knowledge into practical conservation action. The incursion of non-native mammals into Britain is a major threat to water voles and red squirrels, two of our fastest declining species, and resolving the complex issues around how we deal with this problem is a vital component in preventing their extinction."

Ethics and public opinion play a large part in the control of non-native mammals and will continue to feed the ongoing debate about the Britishness of new mammal arrivals. Perhaps the best example to illustrate this point is the public's love-hate relationship with some invaders, such as the grey squirrel who competes with native red squirrels and causes forestry damage, yet entertains young and old alike with its acrobatic antics.

Read about another PTES project promoted by Firebird PR: MoleWatch