Alien Species Are Now Causing Global Extinctions, Scientists Find

Let’s hope an alien species never comes to Earth to compete with humans. A new study from the University College London’s (UCL) Center for Biodiversity and Environment Research has suggested that such an occurrence would mean our chances of survival could be slim.

According to researchers at University College London, alien species–those who are not endemic or native to a particular environment–have been the primary driver of extinctions affecting both plants and animals across the globe.

The study, published Monday in Frontiers in Ecology and the Environment, looked at 953 extinctions that have occurred since 1500 AD. Of those extinctions, 126, or 13 percent, were caused by an alien species. A total of 300, or 42 percent, were caused in part by the arrival of an alien species.

In a statement, lead researcher Tim Blackburn of UCL Biosciences explained:

“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.

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 relied on data from the 2017 International Union for Conservation of Nature (IUCN) Red List that counted the total number of species that had met their demise since the year 1500. The list categorizes the primary drivers of extinction into a dozen categories such as alien species, native species, biological resource use such as hunting and harvesting, and agriculture.

Out of the IUCN list, alien species as primary driver ranked far ahead of the second place extinction driver, biological resource use, which played a role in 18.8 percent of those species lost.

Out of the 782 animal species lost on the IUCN list, 261 were due to alien species. Meanwhile, 39 of 153 plant species went extinct due to aliens. In contrast, only 2.7 percent of animals and 4.6 percent of plant extinctions were caused by native species–less than one-twelfth of those lost to aliens.

Mammalian predators such as “black, brown and Pacific rats and feral cats” were among the primary offenders, with many of them stowing away on boats and causing “island habitats [to be] hit the hardest.” Meanwhile, such predators as cats and foxes were introduced to foreign habitats “deliberately,” the press release notes.

Alien plants such as plantation tree species and ornamental garden plants were also deliberately introduced, before they subsequently “spread and threaten[ed] the native flora and fauna around them.”

Yet while the study relies on the exhaustive data collected by the IUCN, the origin of many species remain unknown, compelling scientists to believe that they may be underestimating the damage caused by alien species.

Professor Blackburn explained:

“It is more likely that [many species] 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.”

While extinction is a natural phenomenon on Earth, happening at a natural rate of around one to five species per year, conservationists and scientists have warned that our planet is currently experiencing the sixth mass extinction of plants and animals in the past half-billion years, with human-caused factors such as climate change and the introduction of alien species driving most mass die-offs.

According to current estimates, the Earth is losing anywhere from 1,000 to 10,000 times the species than the natural “background” rate, with up to dozens of species meeting their final demise each day.