'Alien mammal' invasion of Europe

Raccoon: BBC Nature Raccoons have entered Sweden

Alien mammals, including mink, wild boar, racoons, shrews and beavers, have invaded Europe to a greater extent than we thought.

A new study has found that 71 mammal species have invaded Europe since Neolithic times, while another 30 species have successfully extended their ranges across the continent.

At least 58 of these species directly harm either human health or the environment, according to the report published in the journal Integrative Zoology.

Destructive force

American mink: BBC Nature

The study was conducted by Piero Genovesi and colleagues at the Institute for Environmental Protection and Research in Rome, Italy, and Riccardo Scalera of the Invasive Species Specialist group of the International Union for the Conservation of Nature (IUCN) based in Valby, Denmark.

The research follows up on previous work that examined which alien mammal species have invaded Europe since around AD1500.

In the latest report, the researchers widened the study period to account for species that have invaded since 2007, the end of the previous study period, and before the 1500s, going back to Neolithic times.

They particularly focused on alien outsiders that now threaten native biodiversity.

Alien mammals have been introduced into Europe on at least 740 occasions, the study found.

For 635 of those, the researchers could reconstruct the date of introduction.

For example, wild boar were introduced into Sicily in the Neolithic age, while humans took lesser and greater white-toothed shrews to Cyprus, and Sardinia and the Balearics respectively, around 9000 to 8000BC.

Wild boar: BBC Nature Running wild in UK woodlands

Most recently, in 2009, American red squirrels escaped into Denmark, probably from a commercial pet breeding facility.

In 2010, Canadian beavers were introduced to Belgium and Luxembourg, while in the same year raccoons arrived in Sweden.

Raccoons were also illegally released into Ireland in 2011.

Cats and goats

The UK ranks among the three most invaded regions, with 18 alien mammal species having colonised its shores. The other two are also islands, with 21 alien species establishing themselves in Sardinia and 19 in Corsica.

Domestic cats, feral goats and American mink are among the most damaging invaders, according to the study.

Cats and mink hunt domestic species and out compete others for food, whereas feral goats can graze and trample natural ecosystems, severely damaging them.

American beaver: BBC Nature Beavers from Canada are loose in Benelux

"The data shows a dramatic increase in invasion rate since the beginning of the 20th Century, which is still ongoing," the researchers say in their report.

The demand for exotic pets is driving many of the introductions, say the researchers.

Some species are also being introduced so they can be hunted.

"The constant increase in mammal reintroductions and the high establishment success rate raise serious concerns," scientists add.

For example, alien mammals severely threaten the futures of a significant number of native species, including some at a high risk of extinction.

The threat of invasive species also comes from within the continent: 38 species already recorded in at least one European location have gone on to invade another, with 30 establishing themselves in their new location.

Nine of the 26 most influential alien mammals are already of European origin, but have colonised new regions, the report says.

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