Villains, Victors and Victims: The Great Invasions of Britain
March 2010. Alien invaders 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.
14 invasive mammal species in the UK
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 (see table), 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.
Effects of `alien’ species
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 invasive species 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.
Rabbits were introduced by the Normans in the
12th century. Photo credit Pauline Tweedy
Globalisation may bring further threats
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.
Water voles and red squirrels threatened
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.”
Some invasive species much more problematical than others
Report author David Macdonald says: “The story of invasive mammals in Britain makes it plain that anybody who thinks conservation problems are something that occurs in exotic, far-off places has completely missed the point. The same issues and dilemmas are rampant is our own back yard. We are all stakeholders in conserving biodiversity, at home and abroad. Britain’s invasive mammals illustrate how intricately biological and ethical problems are interwoven. Our report makes clear that there is no simple, one-size-fits-all solution – not all invasive mammals are equally problematic: the grey squirrel, the American mink, the edible dormouse and Chinese water deer each show that every case is a special case”. He adds: “In general, it’s too late to winkle out the invasive mammals that have established here – so the big lesson learnt is that it’s important to prevent further invasions in future: prevention is better than cure.”
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.
Britain’s great mammal invaders
Species
Native range
UK origin
UK threat/significance
American mink
North America
Fur farms, 1929
Predation of native water vole
Ferret
Europe
Rabbit hunting, 12th C
Hybridisation with polecat
Rabbit
Iberian peninsula
Normans, 12th C
Agricultural pests; prey to natives; but maintains calcareous grassland by grazing
Brown hare
Europe
Romans
UK BAP species since 1995; hare coursing with dogs is illegal
Muntjac
China and Taiwan
Woburn Park, 1901
Pests in conservation woodland
Japanese sika deer
Japan
Zoological Society of London, 1860
Hybridization with red deer; impact on forestry
Chinese water deer
East China and Korea
Whipsnade, 1929
Low impact; UK numbers may represent 10% of global population
Fallow deer
Anatolia
Normans, 11th C
Impact on woodland and arable damage
Grey squirrel
North America
Multiple introductions, 1876
Competition and disease transmission to native red squirrel
Edible dormouse
Europe and Anatolia
Tring, 1902
Potential impact on forestry and nuisance to dwellings
Brown rat
Asia
Shipping, 1720
Pests to agriculture, health and native birds
Black rat
Asia
Romans
Rare in Britain
House mouse
Africa and Asia
Iron Age
Pests to agriculture, health and native species
Red-necked wallaby
South Australia and Tasmania
Whipsnade, 1940s
Potential threat to capercaillie on Loch Lomond island
http://www.wildlifeextra.com/go/news/invasive-mammals101.html
Cryptozoology 