Almost half threatened vertebrates are on islands: study

Researchers found that 1,189 highly threatened vertebrate species — amphibians, reptiles, birds and mammals — breed on 1,288 islands, the study in Science Advances journal said.

The threatened species are listed in the red list issued by the International Union for Conservation of Nature and Natural Resources (IUCN).

“The decline of populations and disappearance of species from islands and freshwater systems are disproportionately more rapid than anywhere else worldwide,” said the study whose lead author was Dena Spatz of the University of California, Santa Cruz. Spatz is also a biologist with the non-governmental group Island Conservation.

The Threatened Island Biodiversity Database developed by the researchers “provides the ability to identify and prioritize conservation actions,” they said.

The researchers were able to determine whether species like rats and cats, harmful to the vertebrates, were introduced into those islands, such as in the case of the Floreana mockingbird.

Floreana mockingbirds are listed on the IUCN’s red list as critically endangered but with a stable population. The several hundred which remain are for now confined to islets where there are no predators.

The bird disappeared in the 19th century from the particular island which bears its name in the Galapagos chain. The Floreana mockingbird’s near-extinction, just several decades after humans arrived, resulted from the introduction to the island of invasive species including rodents and wild cats.

Islands comprise only 5.3 percent of global land area but have hosted 61 percent of known extinctions since 1500.

Wild cats and rodents were in the last centuries responsible for at least 44 percent of the extinctions of birds, small mammals and reptiles.

On some islands, it is possible to prevent the arrival of these harmful species and, in the vast majority, to eliminate the intruders. This has permitted the resurgence of numerous native species threatened with extinction, the study said.

An example is on the small island of Anacapa, off California, where the successful elimination of rats contributed to reconstitution of the Scripps’s Murrelet (Synthliboramphus scrippsi) bird population, and to the recent discovery of the European Storm-petrel.

Although threatened vertebrates represent nearly half of all land-based species in danger of extinction, they are only present on a fraction of the earth’s land and less than one percent of islands, the study said.