Carnivores living near humans can find more than half of their diet in human food sources, according to researchers at the University of Wisconsin at Madison.
This disruption of normal animal feeding habits could endanger ecosystems.
Researchers studied the diets of seven species of predators in the Great Lakes region of the United States: coyotes, red and gray foxes, bobcats, wolves, fishermen and swallows.
Chemical analysis of bone and fur samples they collected from areas as remote as national parks and as populated as the metro Albany, NY, found that more carnivores live near cities and farms, the more human food they eat.
This new reliance on a common human food source could lead to conflicts between carnivores that have evolved to compete for different resources as relationships between different carnivores change. This could have negative impacts on ecosystems that have evolved under the significant influence of powerful predators.
The amount of human food that carnivores ate varied widely depending on location. Those who live in habitats with the most human alteration have found more than 25 percent of their food to be human.
It also varied according to the species. Engaged carnivores like bobcats ate relatively little human food, while generalists like coyotes, foxes, fishermen, and martens in human-dominated landscapes can get more than 50 percent of their food from sources. human.
Jon Pauli, professor of forest and wildlife ecology, and Phil Manlick, graduate student, found that relying on human food sources increased the overlap of carnivores in their competition for food.
In addition to increased competition and the resulting higher number of conflicts between carnivores, dependence on human food could make carnivores more vulnerable to humans and alter their normal hunting behavior.
Pauli and Manlick studied the diets of nearly 700 carnivores using bone and fur samples collected with the help of other citizen science researchers and trappers.
Thanks to the quirks in how plants incorporate carbon as they grow, a sample of bone or fur is enough to get a glimpse into an animal’s diet. Different weights, or isotopes, of carbon are common in different plants – and in the animals that ultimately eat them.
“Isotopes are relatively intuitive: you are what you eat,” Manlick explained. “If you look at humans, we look like corn. “
Human foods, rich in corn and sugar, give them distinctive carbon signatures. In contrast, the diets of prey species in nature confer their own carbon signatures. The ratio of these two isotopic footprints in a predator’s bone can tell scientists how much of their diet comes from human sources, either directly or from their prey that first ate human food.
The geographic scope of the study and the large number of species examined by conservationists demonstrate that the trend of food subsidies in the diet of carnivores is not confined to a single location or species.
“When you change the landscape so radically in terms of one of a species’ most important attributes – its food – it has unknown consequences for the overall structure of the community,” said Pauli. “And so, I think it’s incumbent on us now, as conservationists and biologists, to start understanding these new ecosystems and start predicting who’s the winners and who the losers.”
Contact Marcus Schneck at [email protected]pennlive.com.