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Species adjusting with climate

As the planet's climate warms, scientists are discovering more species that are expanding their ranges northward. Others are adjusting their migrations, reproduction or other behaviors to accommodate the earlier arrival of spring.

Scientists call such adaptation to new conditions "phenotypic plasticity."

A report this week in the journal Science describes evidence from a variety of studies that some species may also be undergoing genetic changes that are helping them and their descendants cope with shifts in the seasons.

But the review, by University of Oregon biologists William E. Bradshaw and Christina M. HolZapfel, also found that the adaptations may not assure their ultimate survival.

Large animals in particular - those with smaller populations and longer life cycles - will experience population declines, and perhaps replacement, by species from the south that are better adapted to heat.

The review cites studies that found genetic changes observed over periods as short as five to 30 years are helping certain mosquito, squirrel and bird species change their migration and reproductive habits in response to earlier spring weather.

But some species are clearly having more difficulty than others. For example, despite genetic and phenotypic change, only some great tits, a European bird species, have been able to adjust to the earlier emergence of the caterpillars they eat.

"The average lifetime reproductive success of the population as a whole is declining," the authors conclude. "The population cannot keep pace with environmental change and may be vulnerable to extinction. Hence, the ability to evolve in response to recent climate warming does not, in itself, ensure that a population will survive."

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