Chemical traces in animals’ droppings reflect recent shifts in food consumption
Chemical signatures in a gorilla’s feces reveal a lot about short-term changes in its diet, a new study finds.
What an animal eats tells scientists how it survives in its habitat and adapts to environmental changes. But observing animals dining in the wild isn’t always practical. Now, researchers have tracked monthly shifts in the diets of wild mountain gorillas by measuring different forms of carbon in the animals’ feces.
Researchers monitored eastern gorillas (Gorilla beringei) in the Bwindi Impenetrable National Park in southwestern Uganda over a 10-month period from 2002 to 2003, collecting the apes’ scat and samples of the animals’ favorite foods — leaves, fruit, fruit peels and wood.
Back in the lab, the scientists subjected the dung and plant foods to a rigorous chemical analysis. Specifically, they measured isotopes, different forms of a particular element, such as carbon. Such isotopes are present in distinct amounts in various foods. By measuring the ratio of two carbon isotopes in the gorilla droppings, researchers reconstructed what foods the apes had been feasting on at different times of year, noting a peak in fruit consumption from February to March and from June to July. The study appears online December 10 in the Proceedings of the National Academy of Sciences.
“Stable isotope analysis has been used (before), but not to study endangered African apes,” says anthropologist Matt Sponheimer of the University of Colorado Boulder, who was not involved in the study. “In addition, [the authors] are trying to address quite subtle questions about diet that go beyond most efforts.”
Other studies have measured isotopes in animal bone, tooth enamel or hair, but these types of measurements tend to reflect average diet over months to years. Using feces instead of animal tissue gets at shorter-term changes in diet, says ecologist Donald Phillips of Oregon State University. And, "it’s a lot easier to get samples than if you had to capture a gorilla every time,” he adds.
Isotope analysis is not a replacement for field observation, however. It can’t tell scientists exactly which foods an animal ate, and feces don’t provide information about nutritional value. Still, it’s a useful technique for studying animals that are difficult to observe, such as threatened or endangered species, says study coauthor Scott Blumenthal, an anthropologist at the City University of New York.
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