New research shows that culling invasive, non-native animals on just 169 islands around the world over roughly the next decade could help save almost 10 percent of island-dwelling animals at risk of extinction.

A team of scientists surveyed nearly 1,300 islands where 1,184 threatened native animals have collided with 184 invasive mammals.

Their analyses gave them a list of 107 islands where conservationists could start eradication projects by 2020, potentially keeping 80 threatened species from sliding closer to extinction.

Island-dwelling animals around the globe often face a common threat: alien species that compete with them for food, kill them and their young, and otherwise hamper their ability to survive. Now, new research shows that culling the non-native invaders on 169 islands around the world in the next decade or so could help save almost 10 percent of island animals at risk of extinction.

“Eradicating invasive mammals from islands is a powerful way to remove a key threat to island species and prevent extinctions and conserve biodiversity,” Nick Holmes, the study’s lead author the director of science at the biodiversity conservation nonprofit Island Conservation, said in a statement. “This study is an invaluable global assessment of where these future conservation opportunities exist and [it] supports regional and national decision-making about where and how to prevent extinctions.”

Cats, dogs, rats, pigs and other mammals that have hitched a ride with humans to islands or been intentionally introduced can decimate local species that have evolved in the delicately balanced island ecosystems. In the last five centuries, 75 percent of amphibian, bird, mammal and reptile extinctions have occurred on islands, according to the Island Conservation, and invasive animals are the single biggest factor in those die-offs. Today, islands are home to more than 40 percent of the land vertebrates that are listed as endangered or critically endangered by the IUCN — even though islands hold just over 5 percent of the world’s land mass.

Those statistics make islands important candidates for conservation, but where will the investment of precious funding for conservation have the greatest impact?

To answer that question, Holmes and his colleagues looked at nearly 1,300 islands around the world where 1,184 threatened native animals have collided with 184 invasive mammals. They then ranked the islands, accounting for how much the invasive species were threatening native animals, how important those animals were to the local ecosystem, their risk of extinction and the possibility of eradicating the non-native animals.

Then, they looked at the human side of the equation — whether other eradications had been successful, for example, and how well such a conservation program might be accepted by local and national authorities.

Those analyses gave them a list of 107 islands where conservationists could start eradication projects by 2020, potentially keeping 80 threatened species from sliding closer to extinction. Another 62 islands could begin projects by 2030. (The team “masked” certain sensitive islands where disclosing a location might put animals at further risk from poachers.)

The researchers published their work March 27 in the journal PLOS ONE.

Such projects would benefit local ecosystems, along with helping to maintain global biodiversity, coauthor Piero Genovesi said.

“Through the UN Convention on Biological Diversity and the UN Sustainable Development Goals, the global community has agreed to halt the loss of biodiversity and preventing extinctions by 2020,” Genovesi, an ecologist and senior scientist with the IUCN Invasive Species Specialist Group, said in the statement. “Eradicating the non-native invasive species on the priority islands identified through this research would significantly contribute towards meeting this important target.”

The team’s research also provided further proof that eradication works. On 260 islands, they found no traces of invasive animals, and of those, more than a third had had successful eradications in the past.

“This research highlights an extraordinary opportunity to deliver disproportionate conservation benefits from applying proven methods of island restoration,” Stuart Butchart, chief scientist at BirdLife International, said in the statement. “We can now target conservation funds at the key locations where they will deliver the greatest benefits for native biodiversity.”

Banner image of a rhinoceros iguana by Tommy Hall/Island Conservation.

Citation

Holmes, N. D., Spatz, D. R., Oppel, S., Tershy, B., Croll, D. A., Keitt, B., … Butchart, S. H. M. (2019). Globally important islands where eradicating invasive mammals will benefit highly threatened vertebrates. PLOS ONE, 14(3), e0212128. https://doi.org/10.1371/journal.pone.0212128

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