Global Warming Is Spurring Evolution, Study Says

Richard A. Lovett
for National Geographic News
June 8, 2006
German birds are changing migration patterns. Canadian red squirrels are
reproducing earlier in the year. Mosquitoes in Newfoundland remain
active longer into August.

Traditionally, scientists have viewed such changes simply as behavior modifications in the face of a changing environment—in this case, global warming.

(See National Geographic magazine's "Global Warning: Signs From Earth.")

But scientists say these shifts provide mounting evidence that for some animals, global warming is sparking genetic changes that are altering the ecosystems we live in.

The effect is most striking in the northern latitudes, where climates are becoming more and more like those in the south, researchers say.

(See "Global Warming Fast Facts.")

"Over the past 40 years, animal species have been extending their range toward the poles, and populations have been migrating, developing, or reproducing earlier," said William Bradshaw, an evolutionary geneticist at the University of Oregon in Eugene.

These shifts aren't simply a response to warmer summers but instead reflect recent and rapid changes to the climate at large, Bradshaw and colleague Christina Holzapfel argue in tomorrow's issue of the journal Science.

"The emphasis on summer temperatures is just plain wrong," Holzapfel said.

"Midsummer temperatures in Florida aren't all that different from Fairbanks, Alaska. This is about lengthening growing season and the timing of seasonal events."

Warming and Evolution

Many animals use changing daylight as a signal for when to mate, migrate, or hibernate.

But as global warming makes Alaska more like Mississippi, the cues animals once relied upon will no longer match the climate.

(Read "Global Warming: How Hot? How Soon?")

Bradshaw and Holzapfel cite as an example the European blackcap, a bird that traditionally breeds in Germany and then migrates southwest for the winter to Spain and Portugal.

Some of these birds have begun to migrate west to England, which now has a suitable winter climate, the researchers say.

In the spring, these British birds can beat their Spanish cousins back to Germany, getting dibs on the best nesting sites.

Moreover, Bradshaw and Holzapfel note, the east-west migration pattern is instinctive, indicating that it's now embedded in the British birds' genes.

The upshot, Holzapfel says, is that some animals will be able to adapt to continued climate change, while others will have considerable difficulty.

"Large animals like polar bears will probably do very poorly," she said.

"They have a long life cycle, so it takes them relatively long to adapt genetically."

Over time, she said, "[ecological] communities will become completely different."

Animals and Natural Cues

Other ecologists agree.

The matching of organisms' life cycles to their environments is essential for survival, says Steven Running, forestry scientist at the University of Montana in Missoula.

Global warming, he says, is altering the optimal time for temperature-sensitive activities without changing the daylight cycle in any given place.

The result is a mismatch between the altered climate and the genetically programmed cues upon which organisms currently rely.

The ability of plants and animals to evolve in the face of these changes, Running said via email, "may well define what species are winners and losers in adapting to rapidly changing climates."

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