These disastrous scenarios aren’t guaranteed to happen. In fact, Rogers has been impressed with how resilient ecosystems can be—even on Guam, which she says is an “extreme” example of how profoundly ecosystems can be disrupted and still more or less function. Even when a particular species or type of organism disappears, the ecosystem often can often carry on. Forests may continue to provide a habitat for the organisms that are left—even if it’s a much less ideal habitat than existed before.

Sometimes, in ecosystems that lose ecologically important species, other species—new ones, or ones already present— fill the gaps. But in Guam’s forest, no other species has stepped in to take the birds’ place.

We’ve known for a while that top predators like wolves and tigers are disappearing from landscapes; only more recently have researchers realized that animals that had once been abundant, such as insects, frogs, and bats (all of which can be keystone species), are disappearing, too. Species don’t have to go extinct for them to no longer be able to fill their ecological niche, Rogers points out. Losing a big enough proportion of the individuals in the population might be enough to reduce its ability to fulfill its ecological role. 

Laws intended to protect plants and animals, like the US Endangered Species Act, aren’t designed to take their ecological functions into account. As more of the world’s ecosystems start to look more like Guam’s forests, scientists may push to change that.

There are ways to make a difference without waiting for legal restructuring. On Guam, to get rid of the brown tree snake, researchers and government employees are experimenting with baited traps and have launched rapid response teams when locals spot them (they’re encouraged to call 1-671-777-HISS). Scientists are working with the US military to section off an area of forest on the Air Force base and ensure that it becomes and stays completely devoid of the invasive snakes. There’s talk of bringing the birds back to Guam; Rogers is optimistic. If it’s possible to resuscitate Guam’s forests, maybe we could do the same for other disrupted ecosystems elsewhere in the world.

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