Climate and High-Latitude Herbivores

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“…  the plants on which they depend already have reached their peak
productivity and have begun to decline in nutritional value….”

“… leading to fewer births and to more deaths among caribou calves.”

“”Variation in the landscape provides an insurance policy for
animals, like caribou, that count on being able to climb to the top
of the next hill or go across the next valley to find plants that are
still newly emergent and highly nutritious. Climate change is
reducing the value of that insurance policy,” said Post.
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http://www.sciencedaily.com/releases/2008/05/080521201206.htm
Climate Change Does Double-whammy To Animals In Seasonal Environments

ScienceDaily (May 26, 2008) – Plant-eating animals in highly seasonal
environments, such as the Arctic, are struggling to locate nutritious
food as a result of climate change, according to research that will
be published in the 21 May 2008 online edition of the journal
Proceedings of the Royal Society B. Led by Penn State Associate
Professor of Biology Eric Post, the research, which focused on
caribou, suggests that not only are these animals arriving at their
breeding grounds too late in the season to enjoy the peak
availability of food–the focus of previous research by Post–but
they also are suffering from a reduced ability to locate the few
high-quality plants that remain before these plants, too, become
unavailable.

“This combination of time and space constraints is a double-whammy
for species in highly seasonal environments,” said Post. “Moving
through space–across the landscape–is a strategy used by these
animals to deal with shifts in the time their forage plants are
available, but now climate change is really putting this strategy to
the test,” said Post. “Think of it like this,” he added. “You’ve been
out on the town with friends, and on the way home you want to stop
off for a bite to eat, but the restaurant you’ve always gone to has
closed early. So you try for one around the corner that’s always open
a little longer. But when you get to that one, it too is closed. For
herbivores, the fact that there are several ‘restaurants’–their food
patches–dispersed across the landscape isn’t useful if they all
begin closing at the same time in addition to closing earlier in the
season.”

The team–which also included Christian Pederson, a graduate student
in the Penn State Department of Biology, Christopher Wilmers, an
assistant professor at the University of California at Santa Cruz,
and Mads Forchhammer, a professor at the University of Aarhus in
Denmark–focused their research on caribou in West Greenland as an
example of an herbivore species in a seasonal environment. Closely
related to wild reindeer, caribou are dependent on plants for all
their energy and nutrients. In the spring, they switch from eating
lichens buried beneath the snow to munching the new growth of
willows, sedges, and flowering tundra herbs. As the birth season
approaches, they are cued by increasing daylight to migrate into
areas where this newly-emergent food is plentiful.

Global warming, however, is beginning to undermine this routine.
According to previous research conducted by Post and Forchhammer, the
plants–which initiate growth in response to temperature, not in
response to daylight hours–reach their peak nutritional value
dramatically earlier in response to rising temperatures. When the
animals arrive at their calving grounds now, pregnant females find
that the plants on which they depend already have reached their peak
productivity and have begun to decline in nutritional value.

This “trophic mismatch”–a predicted consequence of climate change in
which the availability of food shifts in response to warming
temperatures–is leading to fewer births and to more deaths among
caribou calves. Now, according to the Post team’s most recent
findings, it is clear that life-cycle timing of plants at the calving
grounds isn’t the only thing with which caribou must contend.
Life-cycle timing of plants in all possible foraging patches also is
advancing as a result of increased temperatures related to global
warming–even those patches that, in the past, might have been
available later in the season.

“Variation in the landscape provides an insurance policy for animals,
like caribou, that count on being able to climb to the top of the
next hill or go across the next valley to find plants that are still
newly emergent and highly nutritious. Climate change is reducing the
value of that insurance policy,” said Post.

This research was funded by the University of Alaska, the National
Science Foundation, and the Committee for Research and Exploration of
the National Geographic Society.

Adapted from materials provided by Penn State, via EurekAlert!, a
service of AAAS.

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