Islands, such as the British Isles, can be adversely affected by the introduction of non-native species. Often an island will have several distinct species not present on the nearest mainland, and vice versa. The native flora and fauna of islands which have been isolated for a longer period of time such as New Zealand or Hawaii (which have been isolated for millions of years) are more vulnerable than islands such as Great Britain and Ireland, which became isolated more recently (8,000 years ago at the end of the Last Glacial Period).
Many species have been introduced to Britain during historical times. Some species such as the midwife toad (Alytes), rainbow trout (Oncorhynchus mykiss), sweet chestnut ( Castanea sativa ) and horseradish (Armoracia rusticana) have been introduced with few adverse consequences. However, others such as the grey squirrel (Sciurus carolinensis), signal crayfish (Pacifastacus leniusculus), and Japanese knotweed (Fallopia japonica) have had a severe impact both economically and ecologically.
In 2010 CABI (Centre for Agricultural Bioscience International) estimated that introduced species in United Kingdom cost £2 billion annually. [1] The most costly species were listed as being the European rabbit and Japanese knotweed. The European rabbit, introduced to Britain by the Romans in 1AD, [2] eats and therefore damages a wide variety of crops and cost the UK £263 million. Japanese knotweed, introduced as an ornamental garden plant in the late 19th century, the roots of which spread by underground rhizomes, can undermine and damage buildings, pavements and roads, [3] cost £179 million. In fact, most mortgage lenders in the UK will demand proof of the plant's eradication from a home owner's property (if signs of it being present are noticed), for it can cause potential physical damage to one's estate. [4] In 2023, it was confirmed that the number of non-native plant species introduced to the UK outnumbered the number of native UK plant species [5]
In addition to the economic costs incurred by management, some introduced fauna displace native species. This can occur by predation, competition for resources, or the spread of disease.
Predation: American mink (Neogale vison), which either escaped or were released from fur farms, prey on native European water voles (Arvicola amphibius) and are drastically reducing their numbers. [6] It was reported that since the late 1980s, 90% of the UK population of the European water vole has been lost, primarily due to displacement and predation by the American mink. [7]
Resource competition: The introduced grey squirrel is larger and more aggressive than the native red squirrel (Sciurus vulgaris) and displaces the native squirrel by competing for food and habitat. Rose-ringed parakeet (Psittacula krameri) populations, originally an Afro-Asian parakeet, have become established in Britain from introduced and escaped birds. There are two main populations: the largest is based around south London, where they can be regularly seen in places such as Battersea Park, Richmond Park, and Greenwich Park; the smaller population can be seen in Surrey and Berkshire, and by 2005 consisted of many thousands of birds, known as the Kingston parakeets. [8] These large parakeets displace native birds species by competing for roosts and nest sites. [9]
Disease: Some introduced species carry diseases to which native species are susceptible. The grey squirrel is a carrier of the squirrel pox virus which kills red squirrels but not grey squirrels. [10] The European crayfish is susceptible to crayfish plague which is spread by the introduced signal crayfish. [11]
Unlike some other environmental problems such as pollution, the effect of an introduced species is not a single event. Once a species has been introduced to an island, the problems may persist and escalate as the species spreads further.
Coypus (Myocastor coypus), large semi-aquatic rodents native to South America, were introduced to the British Isles in 1929 when fur farms were set up in Sussex, Hampshire, Devon and Norfolk. The farms were sited mainly in lowland areas rich in rivers and streams. During the 1930s coypus escaped from captivity and despite repeated attempts to control them, they adapted well to the British habitat, breeding successfully in the countryside of East Anglia. Their habit of building large burrows in river banks caused great erosion damage and threatened the tourism industry where boating is a popular recreation, and caused great damage to drainage works. Coypu were declared to have been successfully eradicated in December 1989 [12] [13] but in 2012 a "giant rat" was killed in County Durham, and authorities suspected that the animal was, in fact, a coypu. [14]
Some species have adapted harmoniously into the ecology of the British Isles. For example, the little owl is not native to the British Isles but was first introduced in 1842, [15] by Thomas Powys and is now naturalised there. However, the presence of some introduced species has proved disastrous for native flora and fauna. There is often a link between how well a species can integrate with an existing ecosystem, and the distance from their local range; i.e. species sourced closer to the sink site tend to cause less damage.[ citation needed ]
Case studies of impact examples can be found at the Non-native Species Secretariat website.
Information on control methods for aquatic species can be found at the GB Non-native Species Secretariat website.
One notable example of a species introduced to the British Isles is the grey squirrel from North America, which out-competes the smaller native red squirrel, as well as carrying a virus that is fatal to the reds. The cost of attempting eradication was reported in 2010 to be £14 million. [1] These attempts have been deemed unsuccessful and priority is now being given to preserving the remaining red squirrel habitats.
The following is a partial list of introduced species. Species marked with a dagger (†) are controlled by The Invasive Alien Species (Enforcement and Permitting) Order 2019, which is the latest legislation.
Molluscs
| Crustaceans |
Ants
| Beetles
|
Two species that prey on earthworms:
Reynoutria japonica, synonyms Fallopia japonica and Polygonum cuspidatum, is a species of herbaceous perennial plant in the knotweed and buckwheat family Polygonaceae. Common names include Japanese knotweed and Asian knotweed. It is native to East Asia in Japan, China and Korea. In North America and Europe, the species has successfully established itself in numerous habitats, and is classified as a pest and invasive species in several countries. The plant is popular with beekeepers, and its young stems are edible, making it an increasingly popular foraged vegetable with a flavour described as lemony rhubarb.
The nutria or coypu is a herbivorous, semiaquatic rodent from South America. Classified for a long time as the only member of the family Myocastoridae, Myocastor has since been included within Echimyidae, the family of the spiny rats. The nutria lives in burrows alongside stretches of water and feeds on river plant stems. Originally native to subtropical and temperate South America, it was introduced to North America, Europe and Asia, primarily by fur farmers. Although it is still hunted and trapped for its fur in some regions, its destructive burrowing and feeding habits often bring it into conflict with humans, and it is considered an invasive species in the United States. Nutria also transmit various diseases to humans and animals, mainly through water contamination.
The signal crayfish is a North American species of crayfish. It was introduced to Europe in the 1960s to supplement the North European Astacus astacus fisheries, which were being damaged by crayfish plague, but the imports turned out to be a carrier of that disease. The signal crayfish is now considered an invasive species across Europe, Japan, and California, ousting native species there.
A number of introduced species, some of which have become invasive species, have been added to New Zealand's native flora and fauna. Both deliberate and accidental introductions have been made from the time of the first human settlement, with several waves of Polynesian people at some time before the year 1300, followed by Europeans after 1769.
Impatiens glandulifera, Himalayan balsam, is a large annual plant native to the Himalayas. Via human introduction it is now present across much of the Northern Hemisphere and is considered an invasive species in many areas. Uprooting or cutting the plants is an effective means of control.
The River Chess is a chalk stream that rises near Chesham in the Chiltern Hills, and flows for 11 miles (18 km) through Buckinghamshire and Hertfordshire to its confluence with the River Colne in Rickmansworth. The Chess, along with the Colne and Gade, gives rise to the name of the district of Three Rivers.
The island of Great Britain, along with the rest of the archipelago known as the British Isles, has a largely temperate climate. It contains a relatively small fraction of the world's wildlife. The biota was severely diminished in the last ice age, and shortly thereafter was separated from the continent by the English Channel's formation. Since then, humans have hunted the most dangerous forms to extinction, though domesticated forms such as the dog and the pig remain. The wild boar has subsequently been reintroduced as a meat animal.
The wildlife of Azerbaijan consists of its flora and fauna and their natural habitats.
Allium triquetrum is a bulbous flowering plant in the genus Allium native to the Mediterranean basin. It is known in English as three-cornered leek or three-cornered garlic, in Australia as angled onion, and in New Zealand as onion weed. Both the English name and the specific epithet triquetrum refer to the three-cornered shape of the flower stalks.
The fauna of England is similar to that of other areas British Isles and lies within the Palearctic realm. England's fauna is mainly made up of small animals and is notable for having few large mammals, but in similarity with other island nations; many bird species.