What they did: The team reviewed more than 1,000 datasets and consulted more than 500 experts worldwide.

• They identified and mapped all 1,189 land-based amphibians, reptiles, birds, and mammals listed as critically endangered or listed on the International Union for Conservation of Nature’s Red List of threatened species that breed on the 1,288 islands around the world.
• They checked which islands had overlapping populations of invasive species, including rats, cats, goats, and pigs, which Spatz called “some of the most damaging invasive species on Earth.”
• The team also gathered some social, ecological and political information that could be of significance for conservation planning.

What they found: “While islands make up only 5.3% of the earth’s landmass, they are home to 41% of the world’s highly threatened vertebrates. A disproportionate amount of threatened species,” she says. Spatz, currently at the non-profit Island Conservation, says she finds it interesting that 95% of all the threatened species in the dataset occurred on at least one island with an invasive vertebrate. Islands with the most highly threatened vertebrate populations include Madagascar, Sri Lanka, Hispaniola and Cuba.

Good news: Dena Spatz comments:

While this may seem daunting, the good news is that there are proven techniques for dealing with the threat of invasive species…and thus management of invasives on these islands could benefit 39% of the Earth’s highly threatened vertebrates.

More perspective: Robert Fisher, a conservation biologist with the U.S. Geological Survey, points out the study is based on highly threatened vertebrates as classified by the IUCN’s Red List, which is incomplete. Fisher, who was not part of this study, says that IUCN so far has only assessed roughly 40,000 out of 61,000 vertebrates and the list does not include species that may be labeled as “data deficient” because they were only assessed once. “We should be investing a lot of money in exploration and discovery right now” to better determine which species are threatened, Fisher tells Axios.

Still, Fisher says the database is a good baseline tool in fighting the extinction of species, which has “cascading effects.” An example of this is on Guam, where brown tree snakes were introduced and killed birds, which led to a huge increase in spider populations.This damaged tourism centered around birdwatching on the island and prompted concerns snakes could similarly invade Hawaii.

Featured Photo: A Critically Endangered Polynesian Ground Dove. Credit: Marie-Helene Burle/Island Conservation
Originally Printed in Axios