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Small Creatures and Climate Change: How Warming Can 'Shuffle the Deck' of Creatures That Thrive

Brenda Ekwurzel

"The American pika may be an early-warning indicator of generally how alpine species may respond to contemporary climate change," said Erik Beever, Ph.D., a wildlife ecologist who has studied pikas for the past 16 years. (pika photo by Flickr user mahalie)

Climate change is messing with mammals. Among other things, it is
shifting their geographical ranges, changing their behavior (or, as
scientists call it, their phenology), and causing disruptions up and
down the food chain. Researchers often look to ancient times for
information about the ways species weathered earlier periods of sudden
warming. Their results provide clues to the kinds of changes we might
expect with further global warming today. New research suggests that
warming may shuffle the deck of biodiversity among small mammals in
North America and change the types of animals that thrive in a
particular place.

In northern California's Samwell Cave, in the foothills of the
Cascade Mountains, researchers examined fossils and learned that
populations of small mammals were severely depleted during Earth's last
emergence from the ice-age world, the late Pleistocene epoch, about
12,000 years ago.
Jessica Blois, a researcher at the University of Wisconsin-Madison, and
Elizabeth Hadly, a professor of biology at Stanford University, found
that although small mammals didn't become extinct during Pleistocene
warming, they did suffer great losses. Certain small mammal species
became extremely rare while others proliferated. And the species that
became king of the landscape, by virtue of its commonness, was the deer

"That is a pretty big, somewhat startling result," Hadly wrote,
noting that deer mice are so common in western landscapes that most
people assume they have virtually always been so. "What these data tell
us is that in the Pleistocene they were not dominant at all."

Though small mammals suffered some losses, a third of their big
mammal cousins (including mastodons, mammoths, and the short-faced bear)
became extinct. The decline in populations led to a lasting ricochet
effect. Each animal in an ecosystem plays an important role, such as
spreading seeds, aerating soil, or being the hunter or the prey. The
decline of gophers and squirrels, for instance, led to the increase in
what Hadly calls the "weed" of small mammals: deer mice. The research
indicates that when diversity shifts the effects are long-lasting. Small
mammals may face huge challenges in surviving the climate changes now
under way.

Creatures under strain from climate change include the American pika,
a rabbitlike animal that lives on talus, or broken rock, in western
alpine mountain regions. When pikas are prevented from regulating their
temperature behaviorally and are exposed to even slight
warming--temperatures of 77 degrees Fahrenheit for six hours--they die.

"The American pika may be an early-warning indicator of generally how
alpine species may respond to contemporary climate change," said Erik
Beever, Ph.D., a wildlife ecologist who has studied pikas for the past
16 years.

New research indicates that pika populations are developing more
resilience to increases in temperature than previous models had
predicted. Constance Millar, a senior scientist with the USDA Forest
Service, examined sites throughout the Sierra Nevada and the
southwestern Great Basin in Nevada and found that the range of the
American pika was larger than prior research indicated. The drier and
lower elevation sites in northwestern Nevada showed losses of pika

One of the most important aspects of Millar's findings is the newly
observed adaptive qualities of pika. Her research indicated that pika
are able to regulate their temperature by burrowing much deeper into the
talus, where cool air circulates. The conditions are much like those in
an air-conditioned home in Arizona: it's scorching outside but cool
indoors. Also, the pikas' foraging behavior is changing. On hot days,
much like rabbits, they search for food at dawn and dusk. On cooler
days, they forage all day long.

Other mammals, she said, haven't been quite as adaptive. Now concern
for the survival of ground squirrels is growing. "We think these may be
more at risk [than pikas]," said Millar. "They don't have this talus to
escape into. They are ground dwelling, so those models about warming
would far more relate to their habitat."

Climate is having an impact on all creatures, great and small. The
polar bear has been the poster child of species loss risk from climate
change, but the emergence of the extremely rare "grolar bear," the
offspring of a grizzly and a polar bear, is new evidence of how climate
affects species. Polar bears are being driven from their usual habitats
on the disappearing polar ice at the same time that grizzlies are moving
farther north because of global warming, resulting in cross-breeding.

Climate-science investigations will continue to aid scientists'
efforts to understand the effects of global warming on animal

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