July 22, 2010

Climate Change Boosts Health, Survival Of Marmots

Longer summers have improved the growth and survival of Colorado's marmots, according to a decades-long study published today in the journal Nature.

The extended summers have meant the large mountain rodents spend less time burning up stored fat during hibernation, giving the yellow-bellied marmots (Marmota flaviventris) an evolutionary advantage by making them heavier and healthier, the study found.

The groundbreaking investigation is the first to reveal that changes in seasonal timing can simultaneously increase body weight and population size in a species. 

Furthermore, the fact that marmots are growing larger, healthier and more plentiful in response to climate change will likely have implications for a host of other creatures, particularly those that hibernate.

"We started this research in 1962, and every summer we'd record basic demography such as the age of the animals, gender, body mass, who survived and who reproduced," said Kenneth Armitage, professor emeritus of ecology and evolutionary biology at the University of Kansas, where the research was founded.

"At the time we started, we had no idea that climate change was going to be a problem. But we collected that basic demography to use as a foundation for other kinds of study."

Yellow-bellied marmots have proven to be a valuable model organism for understanding larger questions.  Armitage said he first chose to study the marmot because it lives in easy-to-find burrows and is active during the daytime, making the rodents readily observable.

"I didn't intend to spend 40 years studying marmots, but new questions kept coming up "” physiological, hibernation, genetics and so on," Armitage said.

"It turned out that long-term studies of our kind are quite rare. Yet, it's precisely the kind of data that you need to determine what climate change is going to do."

The study's findings are the result of a collaborative effort of a number of international researchers who used Armitage's fieldwork to support their analyses.

Arpat Ozgul from Imperial College London and Dan Blumstein of the University of California-Los Angeles worked with Armitage on the project.  Using data collected between 1976 and 2008, the researchers concluded that a longer growing season has enhanced the marmots' individual size, strength and general population.  In fact, the average weight of fully grown marmots surged from 6.82 pounds during the study's early years to 7.56 pounds in the later part of the study.

Meanwhile, the population growth grew from 0.56 marmots per year from 1976 to 2001 to 14.2 marmots per year from 2001 to 2008.

"The warming results in earlier snowmelt, which means that plants appear sooner and the marmots come out of hibernation earlier," Armitage said.

"They have more fat left which provides them energy to start foraging. Then they can start reproducing so their young are born earlier and have time to get fat enough to survive hibernation. Most importantly, the reproductive female can survive better. Being able to wean her young earlier, she has a longer season and survival of adult females has increased over the last years."

Although Armitage is happy to see the yellow-bellied marmot thrive, the KU researcher warned that the surge in marmots is only temporary.  Indeed, he expects that global warming could ultimately harm the rodents over the long run because of changes in snow patterns.

"This benefit to marmots is probably short-lived," the KU researcher said.

"Snow patterns both benefit and harm marmots. Prolonged snow cover in the spring increases mortality and reduces reproduction. But if there's less snowmelt to nourish plants that marmots forage in the summer, it will severely affect them. In droughts, we've had very high mortality."


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