When humans are present and alter environments, non-human creatures are forced to coexist more closely than they would in the wild.
Photos taken by over 2,000 camera traps deployed by the Wisconsin Department of Natural Resources’ Snapshot Wisconsin program were analyzed by researchers at the University of Wisconsin–Madison to predict the closeness of different animal species through time and geography. In regions more often disturbed by humans, the amount of time between camera sightings of distinct species decreased, suggesting that these animals interact with one another more frequently in this setting.
These results, published in today’s issue of the Proceedings of the National Academy of Sciences, give support to the compression theory, which postulates that the expansion of human activity causes animals to live in ever-smaller territories and have more opportunities for interactions. Another theory, known as the expansion hypothesis, suggests that there would be less contacts since humans are dispersing some animal populations at a disproportionate rate.
Author Neil Gilbert, who is now a doctoral candidate in Forest and Wildlife Ecology at the University of Wisconsin–Madison, compares compression to a house party. As the saying goes, the more people you cram into a party, the less elbow room you’re going to have and the higher likely someone is to stomp on your toes.
The presence of humans can be a benefit to certain animals (squirrels and deer, in particular), but it can also cause problems for others. Those animals who would like to avoid human interaction will have to do with less space.
Humans have transformed more than 40% of the Earth’s land area for its uses, urbanized landscapes, agricultural landscapes according to Ben Zuckerberg, study co-author and UW-Madison professor of forest and wildlife ecology. That’s a really significant way in which many species’ habitats are being destroyed, right there.
It’s not always easy to see how habitat loss impacts the social and behavioral dynamics of an animal. If you want to learn about how animals interact in larger groups, you can’t get a comprehensive picture by tagging and tracking only a few of them. Snapshot Wisconsin, a community science effort that invites volunteers to put camera traps on private and public land, has thousands of locations around the state, providing millions of photographs, totaling to near-continuous monitoring of animals moving across a variety of environments.
Jennifer Stenglein, a research scientist at Snapshot Wisconsin and a co-author on the report, explains how the organization helps with “decision making” by providing answers to crucial concerns regarding animals like elk and deer. But when a theoretical researcher like Neil applies some imagination to this massive dataset, it may help move the field forward in exciting ways.
In order to determine the human disturbance within 5 kilometers of each of the nearly 2,000 camera locations, including plots in national forest on the low end and urban development or intense agriculture on the high end, Gilbert downloaded nearly 800,000 animal photos from the Snapshot Wisconsin archive.
In addition, the researchers matched up the 18 observed species into 74 groups, ranking them from low-antagonism (such as skunks and rabbits) to high-antagonism (such as deer and coyotes) based on the possibility that an encounter may turn violent. The researchers then measured how long it took for one animal from a pair to show up at each camera location.
If a camera captures a squirrel and then a coyote a minute later, the two are more likely to engage than if the two were captured three weeks apart.
On average, it took 6.1 days for a pair to be spotted by a camera in low-disturbance environments, but only 4.1 days in high-disturbance ones. The average time between detections was longest for high-antagonism pairs, and the shortest for low-antagonism pairs, but the same pattern held true across all groups: the closer they were to human disturbances, the less time there was between possible encounters.
In ecology, this is a crucial question: how does anthropogenic disturbance and activity influence animal populations? The following questions concern the consequences. Is there a connection to increased disease transmission as a result? How does it affect predators? Does it increase the frequency of car-deer accidents, for example?
Scientists are hoping their findings will shed light on the broader effects humans have when altering not just animal populations but also the size of their habitats.
Neil A. Gilbert et al. (2022). Human disturbance compresses the spatiotemporal niche, Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.2206339119