Brave old world: the debate over rewilding North America with ancient animals

Science News,  Nov 11, 2006  by Eric Jaffe

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For the first time in several thousand years, a lion's roar reverberates through the Grand Canyon. California condors descend into that chasm as though sliding down a spiral staircase. Bolson tortoises creep through spiky yucca plants in the Chihuahuan Desert in New Mexico. Nearby, camels and elephants munch woody shrubs. A cheetah, chasing a pronghorn toward a deep ravine, proves that you can in fact come home again.

If one group of conservation biologists has its way, this is how the western United States could look within the next century: filled with megafauna, including carnivores and herbivores imported from Africa, Asia, and other parts of the world. These animals would repopulate the area where they lived until about 13,000 years ago, when the arrival of people in the region caused them to go extinct.

The plan, called Pleistocene rewilding, suggests reintroducing into Arizona, the Great Plains, and elsewhere various species--such as Bactrian camels, peregrine falcons, and Old World cheetahs--that were once native to North America. If all goes well, these species could reestablish ecosystems that thrived in ancient times, before people began affecting the environment.

When first proposed as a brief commentary in the Aug. 18, 2005 Nature, the idea tickled the imaginations of many journalists. It even earned mention in the New York Times Magazine's "Year in Ideas" issue. However, it also aroused the tempers of some conservation biologists. Now, the same authors have published a more comprehensive follow-up, which appears in the November American Naturalist. The new version presents some compelling reasons to take the plan seriously: Pleistocene rewilding could restore lush ecosystems, curb Lyme disease, and provide a bold alternative to failing models of species conservation around the world.

"We might partially restore these lost taxa and the ecological functions that go with them," says coauthor Harry Greene of Cornell University. "One could imagine, 100 years from now, the American Great Plains turned into an ecological reserve."

But another group of researchers counters that vision. In the October Biological Conservation, a team led by Dustin R. Rubenstein, now at the University of California, Berkeley, challenges the tenets of Pleistocene rewilding, calling it only "slightly less sensational" than Michael Crichton's 1990 novel Jurassic Park (Knopf).

Rewilding could disrupt modern ecosystems just as easily as it could restore historic ones, Rubenstein argues. Once brought from Africa and Asia, genetic relatives of former inhabitants might behave differently than the original species did. A better plan would be to preserve these animals, many of which are endangered, in their native habitats, Rubenstein and his colleagues propose.

"You're putting back species that might be genetically different, and in most cases are, into ecosystems where there haven't been these species in 10,000 years, and the ecosystems have evolved without the species," says Rubenstein. "We need to do something to preserve the species on this planet, but [Pleistocene rewilding] is so bold that it requires different perspectives."

BORN TO REWILD At a New Mexico ranch, Pleistocene rewilding has already begun. Bolson tortoises have been moved there from Mapimi, Mexico--their only remaining wild habitat. During the Pleistocene, these tortoises lived in what's now these Great Plains. People who entered the region in the late Pleistocene preyed on the tortoises, and locals in Mapimi still hunt the l00-pound animals.

Soon, the tortoises will be moved to Arizona, where they will inhabit two 8.5-acre enclosures under heavy supervision, says Joe Truett of the Turner Endangered Species Fund, which runs the New Mexico ranch. Scientists will monitor the tortoises' adjustment and protect young tortoises from ravens, raccoons, and other predators. Tortoise shells don't harden until the animals are about 6 years old.

"The ranch where we're bringing the tortoises has vegetation similar to where they live in Mexico, and the climate's not that much different, either," says Truett. "If they survive the first winter, they'll be fine."

The Bolson project emerged from a meeting held at the New Mexico ranch in September 2004. Ecologist Josh Donlan of Cornell, Greene, and 10 other conservation biologists have summarized that meeting and their plan for Pleistocene rewilding in Nature last year and in the upcoming American Naturalist article.

Most conservation and rewilding efforts focus on animals that went extinct after Columbus came to America, but that approach is flawed, argue Donlan and his coauthors in those publications. It's more logical to use the Pleistocene as a benchmark for conservation, Donlan says. That's when people moved into North America across the Bering land bridge that connects Asia and Alaska. Once they arrived, people began altering habitats and exploiting natural resources. These activities eventually eliminated many species of megafauna.