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2007

A Radical Step to Preserve a Species: Assisted Migration
New York Times, January 23, 2007
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The Bay checkerspot butterfly's story is all too familiar. It was once a common sight in the San Francisco Bay area, but development and invasive plants have wiped out much of its grassland habitat.

Conservationists have tried to save the butterfly by saving the remaining patches where it survives. But thanks to global warming, that may not be good enough.

Climate scientists expect that the planet will become warmer in the next century if humans continue to produce greenhouse gases like carbon dioxide. The California Climate Change Center projects the state€™s average temperature will rise 2.6 to 10.8 degrees Fahrenheit. Warming is also expected to cause bigger swings in rainfall.

Studies on the Bay checkerspot butterfly suggest that this climate change will push the insect to extinction. The plants it depends on for food will shift their growing seasons, so that when the butterfly eggs hatch, the caterpillars have little to eat. Many other species may face a similar threat, and conservation biologists are beginning to confront the question of how to respond. The solution they prefer would be to halt global warming. But they know they may need to prepare for the worst.

One of the most radical strategies they are considering is known as assisted migration. Biologists would pick a species up and move it hundreds of miles to a cooler place.

Assisted migration triggers strong, mixed feelings from conservation biologists. They recognize that such a procedure would be plagued by uncertainties and risk. And yet it may be the only way to save some of the world's biodiversity.

"Some days I think this is absolutely, positively something that has to be done," said Dr. Jessica Hellmann of the University of Notre Dame. "And other days I think it's a terrible idea."

Conservation biologists are talking seriously about assisted migration because the effects of climate change are already becoming clear. The average temperature of the planet is 1.6 degrees Fahrenheit higher than it was in 1880. Dr. Camille Parmesan, a biologist at the University of Texas, reviewed hundreds of studies on the ecological effects of climate change this month in the journal Annual Review of Ecology, Evolution, and Systematics. Many plant species are now budding earlier in the spring. Animals migrate earlier as well. And the ranges of many species are shifting to higher latitudes, as they track the climate that suits them best.

This is hardly the first time that species have moved in response to climate change. For over two million years, the planet has swung between ice ages and warm periods, causing some species to shift their ranges hundreds of miles. But the current bout of warming may be different. The earth was already relatively warm when it began. €œThese species haven€™t seen an earth as warm as this one€™s going to be in a long, long time,€ said Dr. Mark Schwartz, a conservation biologist at the University of California, Davis.

It€™s also going to be more difficult for some species to move, Dr. Schwartz added. When the planet warmed at the end of past ice ages, retreating glaciers left behind empty landscapes. Today€™s species will face an obstacle course made of cities, farms and other human settlements.

Animals and plants will also have to move quickly. If a species cannot keep up with the shifting climate, its range will shrink. Species that are already limited to small ranges may not be able to survive the loss.

In 2004, an international team of scientists estimated that 15 percent to 37 percent of species would become extinct by 2050 because of global warming. €œWe need to limit climate change or we wind up with a lot of species in trouble, possibly extinct,€ said Dr. Lee Hannah, a co-author of the paper and chief climate change biologist at the Center for Applied Biodiversity Science at Conservation International.

Some scientists have questioned that study€™s methods. Dr. Schwartz calls it an overestimate. Nevertheless, Dr. Schwartz said that more conservative estimates would still represent €œa serious extinction.€

Many conservation biologists believe that conventional strategies may help combat extinctions from global warming. Bigger preserves, and corridors connecting them, could give species more room to move.

Conservation biologists have also been talking informally about assisted migration. The idea builds on past efforts to save endangered species by moving them to parts of their former ranges. The gray wolf, for example, has been translocated from Canada to parts of the western United States with great success.

When Dr. Jason McLachlan, a Notre Dame biologist, gives talks on global warming and extinction, €œsomeone will say, €It€™s not a problem, since we can just FedEx them to anywhere they need to go,€™ € he said.

No government or conservation group has yet begun an assisted migration for global warming. But discussions have started. €œWe€™re thinking about these issues,€ said Dr. Patrick Gonzalez, a climate scientist at the Nature Conservancy.

The conservancy is exploring many different ways to combat extinctions from global warming, and Dr. Gonzalez says that assisted migration €œcould certainly be one of the options.€ For now, the conservancy has no official policy on assisted migration.

As Dr. McLachlan began hearing about assisted migration more often, he became concerned that conservation biologists were not weighing it scientifically. He joined with Dr. Schwartz and Dr. Hellmann to lay out the terms of the debate in a paper to be published in the journal Conservation Biology.

Dr. McLachlan and his colleagues argue that assisted migration may indeed turn out to be the only way to save some species. But biologists need to answer many questions before they can do it safely and effectively.

The first question would be which species to move. If tens of thousands are facing extinction, it will probably be impossible to save them all. Conservation biologists will have to make the painful decision about which species to try to save. Some species threatened by climate change, including polar bears and other animals adapted to very cold climates, may have nowhere to go.

The next challenge will be to decide where to take those species. Conservation biologists will have to identify regions where species can survive in a warmer climate. But to make that prediction, scientists need to know how climate controls the range of species today. In many countries, including the United States, that information is lacking.

€œWe don€™t even know where species are now,€ Dr. McLachlan said.

Simply moving a species is no guarantee it will be saved, of course. Many species depend intimately on other species for their survival. If conservation biologists move the Bay checkerspot butterfly hundreds of miles north to Washington, for example, it may not be able to feed on the plants there. Conservation biologists may have to move entire networks of species, and it may be hard to know where to draw the line.

Assisted migration is plagued not only with uncertain prospects of success, but potential risks as well. A transplanted species would, in essence, be an invasive one. And it might thrive so well that it would start to harm other species. Invasive species are among the biggest threats to biodiversity in some parts of the world. Many were accidentally introduced but some were intentionally moved with great confidence that they would do no harm. Cane toads were introduced in Australia to destroy pests on sugar plantations, and they proceeded to wipe out much of the continent€™s wildlife.

€œIf you€™re trying to protect a community of species, you€™re not going to want someone to introduce some tree from Florida,€ Dr. Hellmann said. €œBut if you€™re someone watching that tree go extinct, you€™re going to want to do it.€

Dr. Hellmann and her colleagues do not endorse or condemn assisted migration in their new paper. Instead, they call for other conservation biologists to join in a debate. They hope to organize a meeting this summer to have experts share their ideas.

€œThere really needs to be a clear conversation about this, so that we can lay all the chips on the table,€ Dr. Schwartz said.

Other experts on global warming and extinctions praised the new paper for framing the assisted migration debate. €œIt€™s certainly on everybody€™s mind, and people are discussing it quite a lot,€ Dr. Hannah said. €œThis paper€™s a breakthrough in that sense.€

Dr. Hannah for one is leery of moving species around. €œI€™m not a huge fan of assisted migration, but there€™s no question we€™ll have to get into it to some degree,€ he said. €œWe want to see it as a measure of last resort, and get into it as little as possible.€

It is possible that conservation biologists may reject assisted migration in favor of other strategies, Dr. McLachlan said. But the hard questions it raises will not go away. As species shift their ranges, some of them will push into preserves that are refuges for endangered species.

€œEven if we don€™t move anything, they€™re going to be moving,€ Dr. McLachlan said. €œDo we eradicate them? All of these issues are still relevant.€

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