Mammals and Climate Change

Western Hemisphere Species May Be Displaced

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. A new study by SEFS researchers, published in theProceedings of the National Academy of Sciences,  considers for the first time whether mammals will actually be able to move to those new areas before they are overrun by climate change. Authors are research analyst and SEFS alumna Carrie Schloss, ’11, Associate Professor Josh Lawler, and SEFS alumnus Tristan Nuñez, ’11, now at University of California, Berkeley.

Schloss, the paper’s lead author, says, “When we include the ability of mammals to move to areas with a suitable climate,  we estimate that a safe haven could be out of reach for an average of nine percent of mammals from any given location in the Western Hemisphere, and as much as 40 percent in certain regions, because they won't move swiftly enough to outpace climate change.” Lawler adds, “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.”  In particular, many of the Western 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, the 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 U.N. Intergovernmental Panel on Climate Change.

The 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.  One consideration is how long it takes for members of a species to reproduce. Western Hemisphere primates, for example, take several years before they are sexually mature, contributing to their low-dispersal rate.  In contrast, a single mouse might not get too far because of its size, but if many generations are born each a year, then mice are on the move regularly.  Another reason primates may not be able to keep pace is that some of the territories with suitable climate for primates are expected to shrink, and to reach suitable climate animals in the tropics must generally go farther than in mountainous regions, where animals can more quickly move to a different elevation and a suitable climate. "Those factors mean that nearly all the hemisphere's primates will experience severe reductions in their ranges," Schloss says, "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 says.  The researchers were also conservative, he said, because animals cannot always go in the most efficient direction due to human-made obstacles. “In past eras of climate change the landscape wasn't covered with agricultural fields, four-lane highways, and parking lots, so species could move much more freely across the landscape." 

Focusing on connectivity—linking together areas that could serve as pathways to new territories, particularly where animals encounter obstacles—could help some species keep pace with climate change.   And, says Schloss, “For species unable to keep pace, reducing non-climate-related stressors could help make populations more resilient.  Ultimately, however, slowing the pace of climate change by reducing carbon emissions may be the only way to make sure species will be able to keep pace."

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) . Image: University of Washington.


While bison cross this highway, they and other mammals may be less able to traverse or go around human-dominated landscapes, such as cities, found in the path the animals are taking to territory with climate that suits them.. Photo: Carrie Schloss.