Move Species Threatened by Warming, Scientists Advise

Mason Inman
for National Geographic News
July 17, 2008
People should help species threatened by climate change move to new habitats, researchers argue in a new paper.

Warming temperatures have already sent animals and plants inching toward the poles or climbing up mountains to seek out tolerable habitats.

But many species aren't able to move far enough or will have difficulty fleeing in the future, researchers say. That's because natural barriers such as mountains and deserts block some species, while others are trapped in pockets of forest or other habitats fragmented by cities and cropland.

Now some researchers are supporting an idea called assisted colonization, or actively moving plants and animals to more favorable locations.

"Under these circumstances, the future for many species and ecosystems is so bleak that assisted colonization might be their best chance," the authors write in tomorrow's issue of the journal Science.

But some researchers and conservation groups are skeptical about assisted colonization, arguing that the risk of spreading invasive species is too high. They also say that the practice could favor saving individual species over preserving larger ecosystems.

(Explore an interactive map of what could happen in a warmer world.)


Humans have had a bad track record when it comes to moving species and disrupting environments.

The introduced kudzu vine now chokes much of the U.S. South, and the noxious cane toad has spread successfully across Australia.

That's why any movement should be modest—especially at first—and only employed for species that are well understood, experts say. But it's urgent to sort out the good candidates now, they add.

"Some species are already at risk for extinction due to climate change," said paper co-author Chris Thomas, a conservation biologist at the University of York in the United Kingdom.

Global warming is already changing rain and snow patterns and acidifying the oceans, all of which put a strain on ecosystems, scientists say.

(Related: "Warming May Spur Extinctions, Shortages, Conflicts, World Experts Warn" [April 6, 2007].)

Before any moves are made, however, rules need to be set for how plants and animals will colonize new lands across state or national boundaries, according to Thomas.

"Then we should proceed with a few [species movements] within the next ten years," Thomas said.

"Starting early means that existing populations are still large," he added. "It gets much harder to achieve once only a few individuals are surviving."

Perfect Candidates

The endangered quino checkerspot butterfly "is a perfect candidate for assisted migration" to higher altitudes, said biologist and paper co-author Carmille Parmesan of the University of Texas in Austin.

The unaggressive butterfly is unlikely to overwhelm the plants it eats or crowd out other insects, Parmesan said.

"I wouldn't advocate moving them very far, as if you take a species completely out of it's evolutionary background it can become a huge pest in the new area," she added.

Corals are also ideal, since many species are at high risk and it's hard for them to change habitats quickly on their own.

Placing concrete blocks on the seafloor could give corals a boost in new areas they weren't previously able to colonize, Parmesan said.


But some consider assisted colonization to be an extreme undertaking.

Patrick Gonzalez is a climate change scientist at the Arlington, Virginia-based conservation group the Nature Conservancy.

"We need to employ the range of potential adaptation strategies before considering assisted migration, which is a relatively drastic option of last resort," Gonzalez said.

These other strategies include creating wildlife refuges and corridors to connect patches of land, allowing animals to move freely between them.

(Read: "First Evidence That Wildlife Corridors Boost Biodiversity, Study Says" [September 1, 2006].)

Others say that the practice may favor preserving individual species over whole ecosystems.

Jason McLachlan, an ecologist at Notre Dame University in Indiana, has studied assisted colonization but was not a co-author of the new paper.

"Widespread imposition of assisted migration favors saving species at the expense of saving the natural processes that shape ecosystems and landscapes," McLachlan said.

While assisted migration may save some species, McLachlan said, "there are legal, ethical, aesthetic, and emotional dimensions to the native [plants and animals] of a place."

"We need to rethink conservation in a world that is changing," said Dov Sax of Brown University in Providence, Rhode Island, who studies invasive species.

Moving species to new locations will change or disrupt the existing ecosystems to some degree, Sax said.

"In many cases we can keep these disruptions from causing environmental catastrophes, but occasionally we'll get it wrong," he said.

"The real issue in my mind is whether we can keep the ratio of successes versus catastrophes high enough to make assisted migration worthwhile," he added. "I suspect that we can."

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