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Invading aliens a significant threat to life on Earth, study finds

Invasive alien species, ranging from disease and plants, to rats and goats, are one of the top three threats to life on this planet, according to a new publication coordinated by the Global Invasive Species Programme (GISP). The Juan Fernandez firecrown, threatened by a range of introduced plant and animal species on Isla Robinson Crusoe,...

Invasive alien species, ranging from disease and plants, to rats and goats, are one of the top three threats to life on this planet, according to a new publication coordinated by the Global Invasive Species Programme (GISP).


The Juan Fernandez firecrown, threatened by a range of introduced plant and animal species on Isla Robinson Crusoe, Juan Fernandez Islands, Chile

Photo: Rare Birds Yearbook/Peter Hodum

“Most countries have made international commitments to tackle this threat, but only half have introduced relevant legislation and even fewer are taking adequate action on the ground,” the International Union for the Conservation of Nature (IUCN), a partner of GISP and contributor to the publication, said in a news release about the report today.

The publication, “Global indicators of biological invasion: species numbers, biodiversity impact and policy responses”, looked at 57 countries and found that, on average, there are 50 nonindigenous species per country which have a negative impact on biodiversity, IUCN reported.

The number of invasive alien species ranged from nine in Equatorial Guinea to 222 in New Zealand.

Documented invasive aliens included 316 plants, 101 marine organisms, 44 freshwater fish, 43 mammal, 23 bird and 15 amphibian species.


Mongoose eating a nene, Hawaii’s endangered state bird. Alien predators introduced by humans to Hawaii–including rats, mongoose, dogs, and cats–have caused massive mortality of native birds, according to Hawaii’s Department of Land & Natural Resources.

NGS stock photo by Chris Johns

These numbers are a significant underestimate, according to Melodie McGeoch, lead author on the publication and member of the Centre for Invasion Biology. The center is an association of research organizations, based largely in South Africa, undertaking the science required to reduce the rates and impacts of biological invasions.

Regions with low development status and little investment in research have lower than expected numbers of invasive aliens, McGeoch said. An increase in the number and spread of alien species, which adversely affect the habitats they invade, is nonetheless attributed to a substantial rise in international trade over the past 25 years.

“While some threatened species on the IUCN Red List have improved in status as a result of successful control or eradication of invasive alien species, a growing number are more threatened owing to increasing spread and threats from non-indigenous species,” said Stuart Butchart from BirdLife International. “This shows that although we are winning some battles in the fight against invasive species, current evidence suggests that we are losing the war.”


The akohekohe, threatened by introduced disease-carrying mosquitoes on Maui, Hawaii

Photo: Rare Birds Yearbook/Aaron French

If left uncontrolled, invasive alien species can have a serious impact on native species, IUCN said. “The yellowhead, a bird endemic to New Zealand, has suffered considerably in recent years due to a surge in the number of rats. Two populations of the yellowhead are now extinct and three more are significantly falling in number, leading to the species to move up from Vulnerable to Endangered on the IUCN Red List of Threatened Species.”

Similarly, the pathogenic chytrid fungus, which was entirely unknown until 1998, is thought to be the cause of the decline and extinction of many amphibian populations around the globe, IUCN added. The disease, caused by the fungus, can be spread by humans and a host of other species, ranging from exotic fish to African clawed frogs.


Sea lampreys are a scourge in the Great Lakes of the U.S., where they have no natural predators. They live in both salt and fresh water and likely found their way into the Great Lakes via shipping channels.

NGS stock photo by James L. Amos

The impact of invasive alien species can be successfully controlled, IUCN said. “The black-vented shearwater, a seabird native to Natividad Island off the Pacific coast of Mexico, was under threat from cats, goats and sheep. But since they’ve been eradicated, the status of the bird has been reduced from Vulnerable to Near Threatened on the IUCN Red List.

“Similarly, the control of the red fox in south-western Australia in the last decade allowed the population of the endemic western brush wallaby to recover sufficiently for it to be downlisted on the IUCN Red List to Least Concern.”

“It’s likely to be more cost effective to prevent the spread of invasive species in the first place than to tackle the biodiversity crisis once they have become established,” said Bill Jackson, IUCN’s deputy director general and chairman of GISP. “With sufficient funds and political will, invasive species can be controlled or eradicated. This will allow native species to be saved from extinction, but countries need to dramatically improve the way they deal with the problem.”


A painting of four rat species.

NGS art by William H. Bond

The Global Invasive Species Programme is an international partnership dedicated to addressing the global threat of invasive species. Established in response to the first international meeting on invasive alien species held in Trondheim, Norway (1996), GISP’s mission is to conserve biodiversity and sustain livelihoods by minimising the spread and impact of invasive species.

The GISP publication was produced by scientists from the Centre for Invasion Biology (Stellenbosch University), BirdLife International and IUCN.

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Author Photo David Max Braun
More than forty years in U.S., UK, and South African media gives David Max Braun global perspective and experience across multiple storytelling platforms. His coverage of science, nature, politics, and technology has been published/broadcast by the BBC, CNN, NPR, AP, UPI, National Geographic, TechWeb, De Telegraaf, Travel World, and Argus South African Newspapers. He has published two books and won several journalism awards. In his 22-year career at National Geographic he was VP and editor in chief of National Geographic Digital Media, and the founding editor of the National Geographic Society blog, hosting a global discussion on issues resonating with the Society's mission and initiatives. He also directed the Society side of the Fulbright-National Geographic Digital Storytelling Fellowship, awarded to Americans seeking the opportunity to spend nine months abroad, engaging local communities and sharing stories from the field with a global audience. A regular expert on National Geographic Expeditions, David also lectures on storytelling for impact. He has 120,000 followers on social media: Facebook  Twitter  LinkedIn