"Some mammals may be more vulnerable to climate change than previously anticipated," Carrie Schloss of the University of Washington, US, told environmentalresearchweb. "For example, many primates and shrews and moles will likely be unable to keep pace with climate change across much of their ranges. On the other hand, carnivores such as coyotes or wolves and ungulates such as moose will likely be able to keep pace with changes in climate."

Schloss and colleagues looked at projected rates of climate change and species dispersal for 493 mammals in North and South America. They found that on average 9.2% of mammals at a given location are likely to be unable to keep up. In some places this figure was as high as 39%.

Species are least likely to be able to move in line with climate changes in the tropical and subtropical moist broadleaf forest of the western Amazon; here an average of 14.5% of species will be unlikely to be able to disperse fast enough, the team found.

In the Amazon, the Yucatan Peninsula, the Appalachian Mountains and the south-central US, species are likely to see high velocities of climate change. In some places in the Amazon, the average dispersal velocity for species that won't be able to keep up is 1 km/year but climate change could be as fast as 8 km/year.

In western Mexico and the Midwestern and western US, on the other hand, the velocity of climate change is likely to be relatively low for many species, at 1 km/year, but some have an average dispersal velocity of only 0.1–0.5 km/year.

The team calculated dispersal ability by looking at speed of movement and rate of reproduction; they assumed one dispersal movement per generation. Smaller mammals that cannot move very fast or far may be able to compensate for this by producing several generations each year.

"We use range shift projections as projections of where climate will be suitable for species and then determine how far or how fast a species would need to travel in order to reach these regions of suitable climate," said Schloss. "Range shift projections that do not account for dispersal may be underestimating the vulnerability of species to climate change. For example, in projections that do not include dispersal, some species are expected to expand their ranges, and 58% of these expansions will likely be contractions when the range shifts are limited by dispersal."

Around 87% of mammal species will see reductions in their range, the researchers predict, with one-fifth of these reductions likely to be due to limited dispersal abilities. The average reduction in range will be 37% but primates could lose an average of three-quarters of their range. Many carnivore species and arctiodactyla (even-toed ungulates such as deer and caribou) could gain bigger ranges, however.

The team found that primates and eulipotyphla – shrews and moles – will be least able to keep pace with climate change. Primates are slow to disperse as their young need several years of care before they can reproduce; their tropical habitat means they may also need to move further to reach suitable climates.

Carnivores, arctiodactyla and xenarthra – armadillos, anteaters and sloths – will be best equipped to cope, the researchers believe. These animals have good dispersal ability and are in any case likely to have to move less far.

Land use by humans may also interfere with a species' ability to disperse, for example in the Midwestern and Appalachian regions of the US and south-eastern Brazil. The team calculated that avoiding movement through human-dominated landscapes and large bodies of water could mean animals need to disperse an average of 0.8 km/year faster.

"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."

The researchers reported their work in PNAS.

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