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Monday, October 13, 2008 - 8:09 AM
Louis J. Sheehan, Esquire. Pioneering ecologist Joseph Grinnell in 1914 began a seven year survey
of the animals living in Yosemite National Park in California. Even
then, human impacts such as the transformation of the Central Valley
into an agricultural oasis were changing the landscape and the animals
who lived there.
Nearly a century later, one cause for the transformation of California wildlife has come to overshadow all others: global warming.
Now scientists have found that a rise of 6.7 degrees Fahrenheit (3.7
degrees Celsius) in average nighttime low temperatures (since 1920 when
Grinnell concluded his research) is causing mammals in Yosemite to get
a move on. http://louisejesheehan.blogspot.com
Evolutionary biologist Craig Moritz, director of the Museum of Vertebrate Zoology
(founded by Grinnell) at the University of California, Berkeley, and
his colleagues traced Grinnell's footsteps across the mountainous
Yosemite terrain. Their inspiration: a quote on the wall of the museum
from a 1910 paper authored by Grinnell in which he noted that future
ecologists would be able to use the data he collected to determine how
the same were faring a century later. They found that 16 of the 28
species documented by Grinnell in Yosemite had moved as far as 3,280
feet (1,000 meters) up the slopes in search of suitable climes—and that
at least three, including the alpine chipmunk unique to California, had
edged closer to extinction. http://louisejesheehan.blogspot.com
"The communities [of animals] are going to be very different—which
species co-occur with which species," Moritz says. "That's already very
clear. We can see that now."
The researchers measured populations using updated trapping methods,
such as yogurt cups to lure voles and shrews, at 40 of the same sites
where Grinnell camped nearly a century ago; in cases in which it was
impossible to determine exactly where he had collected his specimens,
"we sampled in similar habitats at the same elevation," says team
member and environmental scientist Steven Beissinger of U.C. Berkeley.
The scientists found that fast-breeding species such as the California
vole and California pocket mouse expanded their ranges by colonizing
higher ground that was no longer as cold at night. Those animals such
as Allen's chipmunk and the bushy-tailed woodrat already living on the
peaks persisted in smaller areas at the highest extent of their ranges
but their habitat had shrank. The alpine chipmunk now lives only 9,600
feet (2,925 meters) above sea level—an upward shift of nearly 2,000
feet (610 meters) from Grinnell's day—leaving it little leeway if the
climate continues warming to move farther up without slipping off the
mountainside entirely.
"I would want to monitor some of these species over the relatively
short-term future, maybe every 10 years, to determine if the trend we
see is continuing," says biologist James Patton of U.C. Berkeley, who
also participated in the survey.
It remains unclear, however, exactly how these tiny mammals will fare
if the average temperature continues to climb at its current rate. As
it stands, the relative diversity of species in any given spot remains
unchanged and closely related species in some cases showed very
different responses—some declining and some thriving. And other species
demonstrated an ability to change preferred habitats. "The most
surprising thing was finding [the] pinyon mouse up in the High Sierra,"
Moritz says about the one-ounce (28-gram) mouse, which researchers
found had jumped from its namesake pinyon pine habitat to higher
elevation forest dominated by white bark pines. "As one of my
colleagues put it: 'What the hell are you doing here?' That was the
first indication that something big might be going on."
Though climate change
is the most likely suspect, researchers fell short of proving it is
behind all these habitat shifts given some puzzling findings. For
instance, "pika
are strongly affected by high temperatures but the average high
temperatures haven't changed," Moritz notes. Nevertheless, the pika's
range has been diminished. "We can't connect the pika physiology to the
observed change yet."
These modern-day researchers hope that future scientists will find
their work as helpful as they found the 4,000 specimens, 3,000 pages of
field notes and 700 photos left behind by Grinnell. But it is already
clear that turning the Yosemite area into a protected National Park in
1890 has permitted species to adapt to this rapid shift in climate by
moving through relatively undisturbed habitats. "What we've looked at
so far is a best-case scenario because we're looking at a protected
landscape," Moritz says. "Community reorganization is a natural
phenomenon but perhaps not at this pace. Can these species adjust to
co-occur or not? I don't know. It's a grand experiment that I sort of
wish wasn't happening." Louis J. Sheehan, Esquire
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