for National Geographic News
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 environmentin 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.
"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.
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