Alien species are the main cause of recent global extinctions

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The rosy wolfsnail (Euglandina roseais just one alien species which has led to species extinctions – initially introduced to Hawaii as a way of controlling African land snails, the species predated on the island’ s endemic snails and is thought to be directly responsible for the extinctions of 134 of these species. © Scot Nelson

Whilst many introduced alien species have little effect on the ecosystems in which they exist, others can have devastating impacts on biodiversity, causing extinctions at local and global scales. However, some scientists argue that the impact of alien species has been exaggerated, and suggest that native species are just as likely to cause extinctions. Researchers from University College London set out to determine if this was the case.

Using data from the 2017 IUCN Red List on the total number of species that are considered to have gone extinct since 1500, the researchers found that alien species were involved in many more extinctions than native species; of the 935 extinctions which occurred since 1500, 300 occurred in some way because of an alien species, with 174 of these occurring solely because of alien species. In comparison, native species were involved in some way in 28 extinctions, although were solely responsible for none.

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The brown tree snake (Boiga irregularis) is an example of an alien species which has caused extinctions  –  since it was accidently introduced to Guam after the second world war, this invasive alien snake is thought to be responsible for the loss of over half of the native bird and lizard species and two of the three bat species found on the island. Photo © Pavel Kirillov

“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.

The IUCN Red List categorises extinction drivers into 12 broad categories such as alien species, native species, agriculture, and biological resource use, such as hunting and harvesting. The researchers found that 33.4% of animal species and 25.5% of plant species had alien species listed as one of their causes of extinction, making alien species the biggest driver of both animal and plant extinctions. Biological resource use was the second biggest driver of extinction associated with 18.8% of animal species extinctions, and 23.5% of plant species extinctions. Native species, by comparison, are listed as an extinction driver in 2.7% of animal extinctions and 4.6% of plant extinctions.

The origin of some species on the list was unknown, and the team assumed they were natives. “However,” Professor Blackburn said, “it is more likely that they are alien. 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.”

The researchers believes better biosecurity is needed to prevent future invasions, and in many cases measures to control or even eradicate alien species must be considered.

For more information on this study, read the article in full: Alien versus native species as drivers of recent extinctions

 

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