What Makes Invasive Species so Damaging on Islands?

Invasive species are a leading cause of extinctions on islands. What makes island ecosystems particularly vulnerable to invasive species?


Many islands are home to species found nowhere else on Earth. If invasive species begin to disturb such islands’ ecosystem balances, the native species being negatively affected have no alternative home or additional populations, and could swiftly go extinct.


The Critically Endangered Juan Fernandez Firecrown is endemic to the Juan Fernandez Archipelago in Chile. Credit: Irene Espinosa/Island Conservation

Specialists have Limitations
Many native island species are considered evolutionary “specialists.” They occupy specific ecological niches. They may have highly specialized diets or behaviors that enable them to survive in the extreme environments that islands often are. Invasive species tend to be generalists—they can survive in a variety of conditions and habitats. If a pair of rodents makes it to an island ecosystem, they may quickly deplete the limited food supply that a native species relies on, or take over its habitat and make its own home there.


A Small Ground Finch (Geospiza fuliginosa) on Floreana Island, Galapagos. Darwin famously studied the specialization and specialization of the Galapagos finches. Credit: Tommy Hall/Island Conservation

Many island species evolved in the absence of predators, meaning they don’t have defense mechanisms that other species might have, such as flight, camouflage, poison, or weaponry. If invasive predators enter an island species’ habitat, the native species are not equipped to cope with the new threat.


Dodo birds evolved on Mauritius Island without natural predators and were ultimately driven to extinction due to the introduction of invasive species. Credit: Biodiversity Heritage Library

Bound by Water
If a pair of rodents is accidentally introduced to a mainland ecosystem, the native species of the region will try to adapt and may open up their range to avoid the unwanted predator. On an island, the only available habitat is limited to the terrain bounded by water. Even species that are able to swim or fly have evolved to return to these islands year after year. On an island, even one pair of rodents can quickly proliferate, thoroughly infiltrating what was once safe, healthy habitat for native species.


Aerial view of Desecheo Island, Puerto Rico. Credit: Tommy Hall/Island Conservation

Featured Photo: White Tern Egg, Midway Atoll. Credit: Wes Jolley/Island Conservation

About Island Conservation

Island Conservation prevents extinctions by removing invasive species from islands. To date, we have successfully restored 60 islands worldwide, benefiting 1090 populations of 399 species and subspecies. Working together with local communities, government management agencies, and conservation organizations, we select islands that have the greatest potential for preventing the extinction of globally threatened species.

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