Black bears in Yosemite National Park that don’t seek out human foods subsist primarily on plants and nuts, according to a study conducted by biologists at UC San Diego who also found that ants and other sources of animal protein, such as mule deer, make up only a small fraction of the bears’ annual diet.
Black bears in Yosemite National Park that don’t seek out human foods subsist primarily on plants and nuts, according to a study conducted by biologists at UC San Diego who also found that ants and other sources of animal protein, such as mule deer, make up only a small fraction of the bears’ annual diet.
Their study, published in this week’s early online edition of the journal Methods in Ecology and Evolution, might surprise bear ecologists and conservationists who had long assumed that black bears in the Sierra Nevada rely on lots of protein from ants and other insects because their remains are frequently found in bear feces. Instead, the researchers believe that bears likely eat ants for nutrient balance.
Rather than relying on indigestible foods found in bear feces for information about the importance of digestible bear foods, the UC San Diego ecologists looked at the digestible foods that were used to produce bear tissue. They accomplished this by measuring the abundances of carbon and nitrogen isotopes found in different species of plants and animals, and used a statistical approach to relate them to the carbon and nitrogen isotopes measured in bear hair. This allowed the scientists to quantify what the bears ate, then assimilated into their hair.
The scientists also applied the same technique to Norway rats in Alaska’s Aleutian Islands and determined that this invasive species subsisted largely on terrestrial plants and seasonal pulses of marine amphipods, rather than marine birds as had been long assumed.
“Rats tend to dominate the habitats they invade on islands, killing much of the native fauna, especially birds, which is a serious conservation issue,” said Carolyn Kurle, an assistant professor of biology at UC San Diego who conducted the study with Jack Hopkins, a postdoctoral fellow. “Using stable isotopes, we confirmed that marine birds have been extirpated to such levels on the islands where we worked that rats don’t eat them anymore.”
“Both rats and black bears are omnivores with complex diets consisting of both plants and animals,” said Hopkins. “To our knowledge, no study before this has accurately estimated the relative importance of plants and animals to the diets of these omnivore populations.”
Continue reading at UC San Diego News Center.
Black bear image via Shutterstock.
