A new study from UC Santa Cruz has revealed that 33 percent of mammal species respond negatively to human presence and struggle to live alongside people. By contrast, 58 percent of mammals were found to live successfully in places with higher levels of human disturbance.
The researchers analyzed data from 3,212 camera traps to show how human activities may be shifting the makeup of mammal communities across North America.
The team was particularly interested in understanding how mammals respond to different types of human disturbance, and whether these responses are linked to traits such as body size, diet, and reproductive success.
In previous work, the researchers observed how wildlife in the Santa Cruz Mountains respond to human disturbance. They found that species like pumas and bobcats are less likely to be active in areas where humans are present, while deer and wood rats become bolder and more active.
The experts set out to investigate which mammals are best equipped to live alongside humans on a larger scale. They combined their local camera trap data with that of researchers throughout the United States, Canada, and Mexico.
Overall, the team tracked 24 species across 61 regionally diverse camera trap projects to look for trends on a continental scale.
“We’ve been very interested for a long time in how human disturbance influences wildlife, and we thought it would be interesting to see how wildlife in general are responding to similar anthropogenic pressures across North America,” said study senior author Professor Chris Wilmers.
The findings showed that grizzly bears, lynx, wolves, and wolverines were less likely to be found in more developed areas, and were less active at these sites. Moose and martens were also less active in areas with a higher development footprint.
On the other hand, raccoons and white-tailed deer were more likely to spend time in developed areas, and were also more active in these spaces.
Overall, mammals that were smaller, faster-reproducing, and had generalist diets were the most positively associated with human disturbance. Black bears, bighorn sheep, and wolverines were more likely to be found in areas frequented by humans, while deer, bobcats, grey foxes, pumas, and wolves were more active in these sites.
The study results indicate that most mammals are willing to tolerate some level of human recreation in order to remain in high quality habitats.
However, the research also shows that there is a limit to how much human disturbance animals can withstand. For example, red foxes were the only animals in the study that seemed to continue to be more active or present at medium to high levels of human disturbance.
In order to maintain suitable habitats that support diversity in mammal populations for the future, it will be important to understand the cutoff at which the costs of having humans nearby outweigh the benefits, explained the researchers.
“From a management perspective, I think the thresholds that we’ve started to identify are going to be really relevant,” said Suraci. “This can help us get a sense of how much available habitat is actually out there for recolonizing or reintroduced species and hopefully allow us to more effectively coexist with wildlife in human-dominated landscapes.”
The study is published in the journal Global Change Biology.