Although human activity has had a huge effect on the natural world, a new study from North Carolina State University shows that climate is still the most influential factor in determining where mammals can thrive. The work sheds light on how climate change will affect wildlife populations.
Roland Kays, lead author of a paper on the work, said the aim of the study was to compare the importance of climate versus human factors in where mammals chose to live. To do this, researchers collected data on 25 mammal species at 6,645 locations across the United States. The study is one of the largest analyzes of camera trap data ever conducted. The data comes largely from Snapshot USA, a national mammal camera trap survey conducted with collaborators across the country.
“One of our ideas was that perhaps humans have changed our landscape so much that we have become the primary determinants of which animals live where,” says Kays, a research professor at NC State and a scientist at the NC Museum of Natural Sciences. “What we found was that humans were in fact not the most important factor. Climate, including temperature and precipitation, was the most important factor in most of the species we observed.”
However, human activity in the form of large population centers and agriculture was still a major factor in where mammals chose to live. Some species struggled in the presence of cities and farms, Kays said, but many species thrived.
“There are many species that do well around people. For example, the eastern gray squirrel is the most common squirrel in Raleigh, and it does very well around people. But there is another species that is the eastern fox squirrel, and it also does well in agriculture, but not so well around people,” he said. “We can see those differences in many other species. The snowshoe hare does poorly around both people and agriculture. This study allows us to see which species are sensitive to our impact, and which ones benefit from it.”
This information helped researchers create maps that predict how common different mammals are in the contiguous U.S., allowing them to divide the country into regions based on the types of mammals that were common in each area. These regions, known as ecoregions, are often used in studying plants, but have never before been applied to mammal populations.
“If you look at something like the eastern deciduous forest, that’s an ecoregion that is classified based on how common a tree species is,” Kays said. “We can now do that with mammal species and then compare that to the plant ecoregions. What we found was a striking similarity between the two. In the east, for example, where there is more rain, more plants grow. That corresponded to a greater abundance of mammals that we also saw in that region, because more plants mean more food for those animals to eat.”
The open access paper ‘Climate, food and people predict communities of mammals in the United States’ is available to read in Diversity and distributions. By identifying climate as the most important influence on mammal habitat choice, the study presents a new tool for predicting the impacts of climate change on mammal populations. Rising global temperatures will cause shifts in where animals can live, affecting precipitation levels and plant growth. Understanding these factors will be important for making sustainable decisions about mammal population management in the future.
