Alien species are the largest driver of recent extinctions

Alien species are the largest driver of animal and plant extinctions since 1500, according to a new survey.

Scientists at the University College London analyzed data related to 953 global extinctions listed by the International Union for Conservation of Nature. Their survey showed 300 extinctions were at least partially to blame for the species demise. Of the 300 extinctions, alien species were solely to blame for 42 percent -- 126 extinctions.

Native species were linked with only a small percentage of animal and plant extinctions.

"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," lead researcher Tim Blackburn, a professor of biosciences at UCL, said in a news release.

"Our study provides a new line of evidence showing that the biogeographical origin of a species matters for its impacts," Blackburn said. "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."

Alien species are linked with nearly a third of all extinctions, making invasive plants and animals the leading driver of extinctions. The next largest driver is biological resource use, hunting and harvesting, which is at least partially to blame for 18 percent of all extinctions.

Scientists published the results of their survey in the journal Frontiers in Ecology and the Environment.

Rats and feral cats, which are often accidentally introduced to island environments, have been especially destructive to fragile, isolated ecosystems. In Australia, feral cats and foxes are responsible for several extinctions.

Introduced plants, whether plantation trees or ornamentals, can also quickly outcompete native species, or spread diseases to local flora.

The origins of some species are unknown, but researchers operated under the assumption that they were native.

"However, it is more likely that they are alien," Blackburn said. "Our results are therefore conservative in terms of the extent to which we implicate alien species in extinction. Also, many regions of the world have not been well-studied, and there are likely to be further extinctions that haven't been captured in these data."

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