The percentage of mammal species unable to keep pace with climate change
in the Americas range from zero and low (blue) to a high of nearly 40
percent (light orange).
A safe haven could be out of reach for 9 percent of the Western
Hemisphere's mammals, and as much as 40 percent in certain regions,
because the animals just won't move swiftly enough to outpace climate
change.
For the past decade scientists have outlined new areas suitable for
mammals likely to be displaced as climate change first makes their
current habitat inhospitable, then unlivable. For the first time a new
study considers whether mammals will actually be able to move to those
new areas before they are overrun by climate change. Carrie Schloss,
University of Washington research analyst in environmental and forest
sciences, is lead author of the paper out online the week of May 14 in
the Proceedings of the National Academy of Sciences.
"We underestimate the vulnerability of mammals to climate change
when we look at projections of areas with suitable climate but we don't
also include the ability of mammals to move, or disperse, to the new
areas," Schloss said.
Indeed, more than half of the species scientists have in the past
projected could expand their ranges in the face of climate change will,
instead, see their ranges contract because the animals won't be able to
expand into new areas fast enough, said co-author Josh Lawler, UW
associate professor of environmental and forest sciences.
In particular, many of the hemisphere's species of primates –
including tamarins, spider monkeys, marmosets and howler monkeys, some
of which are already considered threatened or endangered – will be
hard-pressed to outpace climate change, as are the group of species that
includes shrews and moles. Winners of the climate change race are
likely to come from carnivores like coyotes and wolves, the group that
includes deer and caribou, and one that includes armadillos and
anteaters.
The analysis looked at 493 mammals in the Western Hemisphere
ranging from a moose that weighs 1,800 pounds to a shrew that weighs
less than a dime. Only climate change was considered and not other
factors that cause animals to disperse, such as competition from other
species.
To determine how quickly species must move to new ranges to
outpace climate change, UW researchers used previous work by Lawler that
reveals areas with climates needed by each species, along with how fast
climate change might occur based on 10 global climate models and a
mid-high greenhouse gas emission scenario developed by the UN
Intergovernmental Panel on Climate Change.
The UW researchers coupled how swiftly a species is able to
disperse across the landscape with how often its members make such a
move. In this case, the scientists assumed animals dispersed once a
generation.
It's understandable, for example, that a mouse might not get too
far because of its size. But if there are many generations born each a
year, then that mouse is on the move regularly compared to a mammal that
stays several years with its parents in one place before being old
enough to reproduce and strike out for new territory.
Western Hemisphere primates, for example, take several years
before they are sexually mature. That contributes to their low-dispersal
rate and is one reason they look especially vulnerable to climate
change, Schloss said. Another reason is that the territory with suitable
climate is expected to shrink and to reach the new areas animals in the
tropics must generally go farther than in mountainous regions, where
animals can more quickly move to a different elevation and a climate
that suits them.
Those factors mean that nearly all the hemisphere's primates will
experience severe reductions in their ranges, Schloss said, on average
about 75 percent. At the same time species with high dispersal rates
that face slower-paced climate change are expected to expand their
ranges.
"Our figures are a fairly conservative – even optimistic – view
of what could happen because our approach assumes that animals always go
in the direction needed to avoid climate change and at the maximum rate
possible for them," Lawler said.
The researchers were also conservative, he said, in taking into
account human-made obstacles such as cities and crop lands that animals
encounter. For the overall analysis they used a previously developed
formula of "average human influence" that highlights regions where
animals are likely to encounter intense human development. It doesn't
take into account transit time if animals must go completely around
human-dominated landscapes.
"I think it's important to point out that in the past when
climates have changed – between glacial and interglacial periods when
species ranges contracted and expanded – the landscape wasn't covered
with agricultural fields, four-lane highways and parking lots, so
species could move much more freely across the landscape," Lawler said.
"Conservation planners could help some species keep pace with
climate change by focusing on connectivity – on linking together areas
that could serve as pathways to new territories, particularly where
animals will encounter human-land development," Schloss said. "For
species unable to keep pace, reducing non-climate-related stressors
could help make populations more resilient, but ultimately reducing
emissions, and therefore reducing the pace of climate change, may be the
only certain method to make sure species are able to keep pace with
climate change."
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