- Though the approximately 465,000 islands on planet Earth represent just over five percent of total global land area, they are disproportionately rich in threatened biodiversity — and researchers have now identified which are the most important to protect from invasive species, a major driver of species extinction on islands.
- Researchers found that there are 1,189 “highly threatened” vertebrate species — 319 amphibians, 296 birds, 292 mammals, and 282 reptiles listed as Critically Endangered or Endangered on The IUCN Red List of Threatened Species — that breed on 1,288 of the world’s islands.
- Conservation interventions like prevention, control, and eradication of invasive vertebrates could benefit 41 percent of the world’s highly threatened terrestrial vertebrates that are largely confined to islands, the researchers determined.
Though the approximately 465,000 islands on planet Earth represent just over five percent of total global land area, they are disproportionately rich in threatened biodiversity — and researchers have now identified which are the most important to protect from invasive species, a major driver of species extinction on islands.
A 2015 study found that 61 percent of all species extinctions recorded since 1500 and 37 percent of all species currently listed as critically endangered are confined to islands. Invasive species are one of the largest threats to terrestrial species that call islands home, in addition to habitat loss, but the study’s authors note that “Proven management actions can reduce these threats, benefiting both local peoples and species diversity on islands.”
In order to aid in the planning of the types of conservation efforts that can help prevent further island-based extinctions, a team of researchers led by Dena Spatz, a conservation biologist at Santa Cruz, California-based NGO Island Conservation, identified which islands around the world harbor both threatened terrestrial vertebrates and invasive species like rodents or cats (Spatz began the project while a student at the University of California, Santa Cruz). The researchers have compiled their findings in an interactive distribution map called the Threatened Island Biodiversity Database.
“The opportunities to prevent extinctions are now laid out right in front of us,” Spatz said in a statement. “This knowledge base of threatened island biodiversity can really empower more efficient and better-informed conservation planning efforts, which is exactly what our planet needs right now.”
Spatz and team published a study in the journal Science Advances last October detailing the results of their analysis, which included a systematic review of over 1,000 datasets, publications, and reports in addition to interviews with more than 500 experts in native and invasive species on islands.
They found that there are 1,189 “highly threatened” vertebrate species — 319 amphibians, 296 birds, 292 mammals, and 282 reptiles listed as Critically Endangered or Endangered on The IUCN Red List of Threatened Species — that breed on 1,288 of the world’s islands. Some 829 of those species breed on just a single island.
Invasive species occur on 779 of the islands with highly threatened vertebrates, according to the study, but many of these islands, especially those with threatened reptiles or birds, were found to be smaller and subject to fairly minimal human habitation or development activities. The team said that this presents a significant opportunity to address the biodiversity crisis. “Invasive vertebrate management on these islands could potentially benefit up to 226 populations of 162 threatened vertebrate species,” they write.
Invasive mammals like cats, goats, pigs, and various rodents occur on 97 percent of the islands that were found to have both threatened and invasive species, with rats being the most common invader, occurring on 609 islands. Conservation interventions like prevention, control, and eradication of invasive vertebrates could benefit 41 percent of the world’s highly threatened terrestrial vertebrates that are largely confined to islands, the researchers add.
Harmful species have not been introduced to all of the islands with threatened wildlife, however. “Invasive vertebrates were absent from 24% of these islands, where biosecurity to prevent invasions is a critical management tool,” Spatz and team write in the study.
The researchers hope that the Threatened Island Biodiversity Database will help conservationists and governmental decision-makers to more effectively target their efforts aimed at preventing species extinction, from the global to the regional level.
“The global nature of the paper offers a comparative look at threats to biodiversity and conservation opportunities,” Spatz said. “Furthermore, it provides national and regional governments and NGOs with critical biodiversity information assembled on a global platform, which can inform and stimulate promotion, fundraising, and action to protect species from extinction.”
CITATIONS
• Spatz, D. R., Zilliacus, K. M., Holmes, N. D., Butchart, S. H., Genovesi, P., Ceballos, G., … & Croll, D. A. (2017). Globally threatened vertebrates on islands with invasive species. Science Advances, 3(10), e1603080. doi:10.1126/sciadv.1603080
• Tershy, B. R., Shen, K. W., Newton, K. M., Holmes, N. D., & Croll, D. A. (2015). The importance of islands for the protection of biological and linguistic diversity. Bioscience, 65(6), 592-597. doi:10.1093/biosci/biv031
