Alien animals and plants are biggest cause of extinctions

The black rat has contributed to the extinction of many species of birds, mammals and reptiles.

Alien species are the main driver of recent extinctions in both animals and plants, according to a new study by UK researchers.

Scientists from University College London (UCL) have concluded that non-native plants and animals have been solely responsible for 126 out of 953 global extinctions in the past 500 years – 13 per cent of the total number studied.

Overall, alien species were a contributory factor in the extinctions of more than a third of all animals and a ­quarter of all plants that have died out since 1500.

In contrast, native species were linked with fewer than three in 100 animal extinctions and just one in 20 plant losses.

The latest figures for the first time put alien species ahead of biological resource use – such as hunting and harvesting – as the leading cause of extinctions worldwide.

“Some people have suggested that aliens are no more likely than native species to cause species to disappear in the current global extinction crisis, but our analysis shows that aliens are much more of a problem in this regard,” said lead researcher Professor Tim Blackburn, from UCL’s biosciences department.

“Our study provides a new line of evidence showing that the biogeographical origin of a species matters for its impacts.

“The invasion of an alien species is often enough to cause native species to go extinct, whereas we found no evidence for native species being the sole driver of extinction of other natives in any case.”

The study used data from the 2017 IUCN Red List on the total numbers of species considered to have become extinct globally since 1500.

The list identifies 12 broad categories of extinction drivers, including alien species, native species, biological resource use and agriculture.

Alien species are been ranked as the top driver of animal extinctions, while biological resource use affected under a fifth of all those lost.

Results show the number of animals wiped out in some part by alien species is more than 12 times greater than those killed off by natives.

Some of the worst invaders have been mammalian predators such as rats and feral cats, spread by human activities.

Some animals first arrived in new places by stowing away on boats, while others have been introduced deliberately.

Many plants have also been intentionally translocated, including plantation trees and ornamental specimens for gardens.

Once in place, aliens often spread rapidly due to a lack of natural restrictions.

They pose a threat to native flora and fauna around them by outcompeting, transmission of diseases and predation.

Findings show island habitats are most vulnerable and have been hardest hit.

It’s estimated that invasive non-native species cost the UK up to £2 billion each year, with a bill of around £200 million for Scotland alone.

American mink, grey squirrels, black rats and signal crayfish are among a number of alien creatures causing trouble for indigenous wildlife.

Problem plants include rhododendrons, Japanese knotweed, giant hogweed and Himalayan balsam.