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

Endemism

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.

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.

Defenseless
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.

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.

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