Giant pandas and red pandas are able to coexist in China, confounding a ecological principle that two species with an identical food source can't live in the same region, scientists say.
Although the two species aren't closely related -- separated by 40 million years of evolution -- they rely on the same food, bamboo, and are found in the same geographic region, they say.
"Scientists have been studying the differences between red pandas and giant pandas for a long time because there's a basic principle in ecology that says if two species of an organism utilize the same resources, they cannot live in the same space," says Z. Jack Tseng of the American Museum of Natural History's Division of Paleontology.
"There's too much competition," says Tseng, one of the authors of a study published in the journal Biology Letters.
Tseng and scientists at the University of Málaga in Spain found the secret of the ability of the two species to coexist is in their skulls, or, more precisely, how each goes about chewing bamboo.
Using biting simulations based on high-resolution images of the skulls, they found differences that have led to distinct preferences in their bamboo feeding habits, with red pandas existing on softer parts of the plant such as leaves while giant pandas seek out the tougher stem parts.
"We've found that fundamentally, based on the structure of their skulls, they cannot eat the same things," Tseng says.
The two panda species are not closely related -- red pandas share an evolutionary history with animals such as weasels and raccoons, while the much larger giant pandas are closer to bears -- but their geographic distributions in the south of China overlap and both have evolved to live on a diet of the identical bamboo species.
While the panda skulls display some similarities, being versatile and robust to allow a variety of chewing actions, the researchers describe some notable differences.
A red panda's skull distributes mechanical stress from chewing more efficiently while a giant panda skull can resist greater forces, they say.
"These differences tie into the way that the species actually process bamboo," Tseng says. "The giant panda is a less-refined eater: it does a lot of chomping and swallowing. Their skulls are stronger overall, so the peak biting stresses are lower, meaning that they can eat harder and larger pieces of bamboo.
"The red panda has a weaker skull but it's better at distributing stresses, allowing it to chew longer and break down soft bamboo leaves more thoroughly before they swallow them."
The preference for different parts of the bamboo plant accounts for the ability of the two distinct species to coexist in the same ranges while requiring the same single food source, the researchers say.
