Global Warming Linked to Caribou-Calf Mortality
Press Release
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Fewer caribou calves are being born and more of them are dying in West
Greenland as a result of a warming climate, according to Eric Post, a
Penn State associate professor of biology. Post, who believes that
caribou may serve as an indicator species for climate changes including
global warming, based his conclusions on data showing that the timing of
peak food availability no longer corresponds to the timing of caribou
births. The study, which was conducted in collaboration with Mads
Forchhammer at the University of Aarhus in Denmark, will be published in
the 12 July 2008 issue of the Philosophical Transactions of the Royal
Society of London.
Caribou - which are closely related to wild reindeer - are dependent on
plants for all their energy and nutrients. Throughout the long Arctic
winter, when there is no plant growth, they dig through snow to find
lichens; however, in spring they rapidly switch to grazing on the new
growth of willows, sedges, and flowering tundra herbs. As the birth
season approaches, they are cued by increasing day length to migrate
into areas where this newly-emergent food is plentiful.
But this routine, which has worked for millennia, is faltering because
caribou are unable to keep pace with certain changes that have occurred
as a result of global warming. Now, when the animals arrive at their
calving grounds, pregnant females find that the plants on which they
depend already have reached peak productivity and have begun to decline
in nutritional value. According to Post, the plants - which initiate
growth in response to temperature, not day length - are peaking
dramatically earlier in response to rising temperatures. "Spring
temperatures at our study site in West Greenland have risen by more than
4 degrees Celsius over the past few years," said Post. "As a result, the
timing of plant growth has advanced, but calving has not."
The phenomenon, called trophic mismatch, is a predicted consequence of
climate change, in which the availability of food shifts in response to
warming, whereas the timing of demand for those resources does not keep
pace. Trophic mismatches have been documented in birds - with the most
famous example being the study on Dutch birds and their caterpillar prey
that was highlighted in former Vice President Al Gore's film An
Inconvenient Truth - but, until now, the phenomenon had not been
observed in terrestrial mammals. "Our work is the first documentation of
a developing trophic mismatch in a terrestrial mammals as a result of
climatic warming," said Post. "And the rapidity with which this mismatch
has developed is eye-opening, to say the least."
While Post and Forchhammer think it is possible that caribou will
respond to a warming climate by advancing the timing of their
reproduction, they are not convinced that the species will be able to
compensate fully for the rapid rates of temperature change that are yet
to come. "They're a little behind the game already and future warming
will make it even harder for them to catch up," said Post. "This factor
is just one of many related to climate change - such as thaw-freeze
cycles, ice-crust formation, and severe storms - that may make it
difficult for caribou populations to persist at their former abundance."
This research was funded by the University of Alaska, the Penn State
Institutes of Energy and the Environment, and the National Geographic
Society Committee for Research and Exploration.
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