One of the bellwether species on the impact of climate change to our environment is the butterfly. Scientists say that warmer temperatures are affecting where butterflies live and breed, causing some species to migrate toward cooler climates near the earth's poles. "Changing Planet" is produced in partnership with the National Science Foundation.
Adaptation of Butterflies
ANNE THOMPSON, reporting:
From Monarch to Checkerspot, Swallowtail to Painted Lady, butterflies are among the most beautiful and celebrated of all insects.
But these tiny creatures add more than just color to our earth. They pollinate plants, add to the biodiversity of our planet, and for scientists, provide vital information about how climate change impacts the environment.
Dr. CAMILLE PARMESAN (University of Texas at Austin): Many butterflies are very, very good indicators of the health of the ecosystem that they’re in. They’re very sensitive so butterflies are often the first to start declining if that habitat is degrading before even the scientist noticed it.
THOMPSON: Camille Parmesan, professor of Integrated Biology at the University of Texas, studies the impact of climate change on butterflies.
She says over the last 30 years, warmer temperatures have forced dramatic shifts in the places where butterflies live and breed - as far as 124 miles, or 200 kilometers, north and south, toward cooler climates.
PARMESAN: What we’re seeing is that area of residency is shifting. It’s not really individuals moving, picking up and moving. It’s that whole populations go extinct on one boundary that’s gone and new populations form at another boundary and the net result is that the whole range shifts.
THOMPSON: One example is the Edith Checkerspot butterfly, found in western North America. At the southern edge of the butterfly's range in Mexico, Parmesan says about 75 percent of the population has died off, compared to less than 20 percent along its northern edge in Canada. At the same time, she says, about 45 percent of the population has died off at elevations below 8,000 feet and less than 20 percent died off at elevations above 8,000 feet. This pattern of extinction tells Parmesan that populations of the Edith Checkerspot shifted higher up and to the north.
PARMESAN: The average location of a population is now about a hundred miles further north than it used to be.
THOMPSON: The reason some butterflies shift and others die off has a lot to do with how adapted a butterfly population is to its habitat, and how much it relies on its host plant.
The life cycle of a butterfly happens in four stages, beginning with an egg attached to the leaf of its host plant. After a few weeks the egg hatches and a caterpillar is born. Once the caterpillar becomes fully-grown, it forms a pupa and undergoes a transformation called 'metamorphosis' in which it remerges as a fully-grown butterfly. Parmesan says warmer temperatures cause some host plants to dry up earlier than usual, which could have drastic consequences for butterfly reproduction.
PARMESAN: By the time the eggs hatch, most of the plants are dry instead of most of the plants being green and a few being dry to that in the ten days that those caterpillars have to feed the whole plant population is in this state, it’s drying up and none of them survive.
THOMPSON: It's a problem that may only get worse. According to the 2007 Consensus from the Intergovernmental Panel on Climate Change, earth's temperature is expected to increase by 3 to 7 degrees Fahrenheit, or 2 to 4 degrees Celsius, over the next 100 years.
Jessica Hellmann, associate professor in the department of biological science at the University of Notre Dame is studying how this temperature change could affect the eggs of the Karner Blue butterfly, an endangered species found near the Great Lakes.
Dr. JESSICA HELLMANN (University of Notre Dame): So we’re literally simulating every day what it’s typically like and then our other chambers then are simulating two degree warmer than that, four degrees warmer than that and six degrees Celsius warmer than that.
THOMPSON: In another experiment, Hellmann and her research students tested how well two populations of butterflies from Vancouver Island, the Propertius Duskywing and the Anise Swallowtail, faired if given the warmer climate of California. Hellmann found that the Propertius Duskywing favored the cooler weather in Vancouver Island over the warmer climate in California.
HELLMANN: They didn’t like the warmer winters and so we think that is the climate becomes more like California in British Columbia in the future, it’s not necessarily going to be a good thing for that particular butterfly.
THOMPSON: Scientists call this preference for a place with specific climate "local adaptation." Butterflies that are locally adapted are less likely to move and more likely to die off when the temperature changes.
HELLMANN: If I was the betting person and I was standing a little bit to the north waiting for these butterflies to arrive from the south due to climate change, I think I might be waiting there for a while.
THOMPSON: But temperature isn't the only factor impacting butterflies. In places like Chicago, Los Angeles and New York, huge urban sprawls now dominate the landscape and limit the number of places where butterflies can live.
PARMESAN: Climate change may be the final nail but if humans weren’t around, if you still had lots of habitat I think they would have been OK even with the amount of climate change we’ve had, but that on top of habitat loss is too much.
THOMPSON: To help species get past these man-made barriers, scientists are exploring the idea of managed relocation, moving a species to an area with a more suitable climate within its range. If the amount of available land continues to decline, managed relocation may be the only way to save some species of butterflies from going extinct.
PARMESAN: That’s what we’re trying to prevent. Not so much prevent what’s happening right this minute, but we want to make sure that we’ve got now will still be there a hundred years from now.
THOMPSON: Making sure that wild species like the butterfly are around to maintain the health and beauty of our planet.
Monarch butterflies, those delicate symbols of spring and summer, should mostly be in Texas by now. In an ordinary year, they would be winging their way to Mexico for the winter.
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