Eradication of Invasive Species: Not Always the Best Option

Sometimes, simply removing an invasive species completely from the habitat it threatens can cause more harm than good. In a changing ecologies, endangered species sometimes adapt to rely on invasive ones, presenting environmental caretakers with a difficult choice.

A study published in Science uses the plight of the California Clapper Rail as an ideal eample of how this can happen.

According to the study, a species of bird only found in the San Francisco Bay region called the California Clapper Rail has been slowly disappearing over the past few decades, to the initial confusion of the US Fish and Wildlife Service.

Looking back on past environmental conservation efforts, researchers found that the Army Corps of Engineers had decided to introduce the hearty cordgrass Spartina alterniflora in an effort to reclaim lost marshland for numerous species in the Bay Area. However, it was soon discovered that this foreign cordgrass could not be easily contained, and it quickly spread to push out and hybridize with native Spartina grasses that the clapper rail depended on for its habitat.

Initially, the bird did not know what to do with this new species, and its populations began to drop dangerously low. In 2005, efforts began to eradicate the invasive hybrid Spartina so that local grasses could recover, however these efforts seemed to hurt clapper rail populations again, reducing them by 50 percent in five years.

Between 2005 and 2011, the study notes, something happened that wasn't expected; the bird had learned to make the new invasive cordgrasses its home. With these invasive grasses getting nearly eliminated, and with local Spartina making an extremely slow recovery, efforts to protect the endangered California Clapper Rail had nearly left it without a habitat at all.

According to co-author Alan Hastings, "just thinking from a single-species standpoint doesn't work."

Using data from the Clapper Rail problem, Hastings and his colleagues modeled a framework that environmentalists can use to balance conflicting preservation goals.

"As eradication programs increase in number, we expect this will be a more common conflict in the future," said paper co-author Ted Grosholz in a recent statement.

This work, he adds, will hopefully help avoid results that almost leave an endangered species like the clapper rail homeless.

The study was published in Science on May 30.