The speed of climate change means that one in ten mammal species in North and South America face a stark challenge: evolve or die out. “As the climate changes, the conditions where a species currently exists may no longer be suitable for it,” explained Carrie Schloss from the University of Washington. “This species can evolve, die, or move.” But some mammals can’t move fast enough to get to areas they’re adapted to, leaving them with just two of those options, Carrie and her fellow scientists have found.
Scientists have already shown that where plants and animals can be found has moved in response to a changing climate. And while many studies have projected species range shifts in the future, they don’t usually consider whether species can get to areas it’s suited to. In part that’s because there isn’t much information on how quickly they can disperse from their homes, Carrie told Simple Climate. But Carrie called on a known relationship between species’ body size and diet and the distance mammals can disperse before their first mating. “In general, larger animals disperse further than smaller animals,” Carrie said. Meat-eating animals also disperse further than same-sized animals eating just plants or plants and meat.
Together with fellow Washington ecologists Josh Lawler and Tristan Nuñez, Carrie combined this dispersal distance with time between each generation for 493 different species in North and South America. The team then worked out how many generations there would be between 1990 and 2100. “Some mammals, like some small mice, may reproduce and the next generation may mature and disperse and reproduce several times within a year,” Carrie explained. “With other mammals, such as primates, the juveniles may not be reproductively mature for a few years.” By combining the number of generations with the pre-mating dispersal distance, Josh, Tristan and Carrie could get an overall figure for how far the mammals could migrate.
With other scientists, Josh had previously shown where average conditions from 2071-2100 would be suitable for each mammal based on projections from ten climate models using a mid-to-high greenhouse gas emission scenario from the UN Intergovernmental Panel on Climate Change. From that he, Carrie and Tristan determine the minimum distance from their current home ranges to the nearest place likely to be suitable in future. Then, in a paper in the research journal Proceedings of the National Academy of Sciences of the USA published this week, they compared that with the total distance mammals could disperse. Further, they also looked at how much human land use – like inhospitable cities – might slow down the needed movement.
Safety was out of reach for one-tenth of the mammals on average, and two-fifths in the tropical forests of the western Amazon region, putting them at increased risk of extinction. “As the climate changes, for many primates and shrews and moles, the location where climate will be suitable will be further than these animals can move,” Carrie explained. The news was better for large hoofed mammals like moose or meat-eaters like coyotes, she added. “These animals can move long distances and will likely be able to move with the climate that is suitable for them as it changes location provided that the landscape also facilitates their movement.”
Such impacts suggest some mammals may be more vulnerable to climate change than previously anticipated, Carrie warns. Projections that don’t include dispersal predict that some species will be able to roam broader ranges as climate changes. Including dispersal suggests that in more than half these cases animals will actually have smaller ranges. In fact, after considering dispersal, ranges will shrink for the vast majority of mammals in the Americas.
Humans will make the difficult journeys even harder, with animals needing to move half a mile a year further to avoid going through landscapes we dominate. This is a particular problem in southeastern Brazil, where mammals would otherwise be readily able to reach suitable destinations. In the midwestern and Appalachian regions of the US, already restricted species dispersal is further limited by our land use.
Carrie suggests that planners could link up areas species need to move between to make it easier for them to keep pace with their favoured environments. Separately, she is now also working on how to plan conservation in a warming world, when plants and animals are on the move. “We are using the diversity of the landscape, which remains stable even in a changing climate, to prioritise areas for conservation,” she said.