As climate warms, species may need to migrate or perish

Smaller ranges may put some species at greater risk of extinction. While scientists can’t make precise predictions about global warming’s effects on biodiversity, their rough estimates are chilling. In 2004, 19 researchers published a paper in Nature in which they concluded that if mid-range projections of global warming prove right, climate change would shrink the ranges of 15 to 37 per cent of all species so drastically that they would be “committed to extinction”.

A conventional strategy for conserving species - such as setting up a preserve where they live now - may not work against global warming. Trying to save the American pika by protecting mountaintops may be futile if the entire mountain gets too warm for them. So conservation biologists began to wonder if they might have to ship species to new places.

They’d done it before. To bring wolves back to Yellowstone, for example, wildlife managers had imported animals from Canada. But in that case and others like it, animals and plants were returned back where they had once been. Managed relocation would require conservation biologists to move species to places where they might never have dwelled, and that’s never been done before.

Jason McLachlan and Jessica Hellmann of Notre Dame University and Mark Schwartz of the University of California at Davis first broached the possibility in the journal Conservation Biology in 2007. They did not endorse managed relocation, but simply argued that conservation biologists should openly discuss the benefits and risks seriously before anyone started to move species around. In 2008, Hellmann, McLachlan, Schwartz, and Sax established a 30-person Managed Relocation Working Group that is working on a detailed analysis of when and how to resort to the strategy.

Managed relocation has also earned some high-profile endorsements over the past year. In July 2008, a group of leading conservation biologists published a piece in Science in which they argued that there might be little choice but to move some species. “The future for many species and ecosystems is so bleak that assisted colonization might be their best chance,” they wrote. Camille Parmesan, one of the co-authors and a biologist at the University of Texas, has pointed to the American pika as a candidate. The Ecological Society of Australia has endorsed managed relocation as well as a way to help species cope with climate change.

Up until now, however, all the talk about managed relocation to defend against climate change has been in the abstract. No one had any hard data on how such a move might turn out. That’s changed now that Willis and his colleagues have published their results from relocating butterflies. (In the same paper, the biologists also describe how they released 600 small skipper butterflies north of their range in 1999 and 2000, with similar success.)

“We think this is the first test,” says Willis. “And we’ve demonstrated it does have the potential to work.”

But Daniel Simberloff, an ecologist at the University of Kentucky, is not impressed. “It seems like this idea is developing into a bandwagon,” he says. “It’s a thing to do, but it doesn’t have a sound scientific foundation.”

In March, Simberloff and Anthony Ricciardi of McGill University in Montreal published a fierce attack on managed relocation in the journal Trends in Ecology and Evolution. Ricciardi and Simberloff’s concerns stem from their decades of research on biological invasions. Humans shuttle many species from their native habitat to a new home each year. Most of the introductions are accidental. A species may hitchhike across an ocean in the ballast water of a ship. Snakes sneak up the wheel wells of airplanes. People sometimes buy pets smuggled in from other countries and then abandon them. On the other hand, some introductions are intentional. Rabbits were brought to Australia by a bored rancher who wanted something to shoot.

Most of the alien species introduced to new places die off. Some establish small populations that don’t disturb the native ecosystem. And others wreak havoc, driving native populations towards extinction.

Invasion biology is a busy scientific discipline (Simberloff is editor-in-chief of a journal, Biological Invasions, dedicated to the topic). But it’s still too young, according to Simberloff and Ricciardi, to predict what will happen to a particular species introduced to a particular place. “I’m skeptical that we’ll ever be really good at it,” says Simberloff. “There are always going to be mistakes.”

Even carefully planned introductions that seem to pose no risk sometimes go awry. Wildlife managers introduced a North American freshwater shrimp into Flathead Lake in Montana to feed kokanee salmon (that were themselves introduced for fishing). The nocturnal shrimp avoided the diurnal salmon and began gobbling up zooplankton the salmon were eating. The salmon population crashed, and so did the eagle population that depended on it.