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A. Between August and April, they sought food in low elevations (海拔) on China's Qinling Mountains. B. Scientists think the research show that pandas are very clever. C. Pandas eat bamboo all day long except when they are sleeping or playing. D. The gene for their “umami taste receptors” became inactive. E. They fed on them until they went back down the mountain and started eating Bashania fargesii leaves again. F. Scientists have conducted many studies on pandas' eating habits. |
Are Bamboo-Eating Pandas Really Herbivores?
On the outside, giant pandas look like herbivores (食草动物). They spend nearly all of their waking hours eating bamboo. But on the inside, they're built like carnivores (食肉动物). About half of the calories they eat come from protein, according to a new study.
The ancestor of giant pandas were omnivorous(杂食的). They are both animals and plants, and had the digestive system and gut bacteria to metabolize(使发生新陈代谢)them. They had "umami taste receptors," to appreciate the flavors of meat.
However, about 2.4 million years ago, things began to change. Their jaw and teeth evolved to help them crush bamboo, and their wrist bone became capable of grasping the stalk(杆)of their favorite plant. Scientists think pandas switched to eating bamboo partly because they didn't have to fight with other animals to get it. Bamboo is high in fiber but has a low concentration of nutrients, so pandas have to eat 20 to 40 pounds of the plant every day just to get by.
David Raubenheimer, a nutritional ecologist at the University of Sydney, and his colleagues put GPS trackers on two giant pandas and followed their movement throughout the year. They discovered that the pandas followed the protein. At the start of the cycle, they ate Bashania fargesii leaves until they got the chance to feast on young shoots, which contained more protein.
The more the shoots grew, the more their protein was diluted(冲淡)by fiber. That caused the pandas to move to higher ground, where Fargesia qinlingensis grew. First, they ate the shoots, but these, too, went from being protein - rich to fiber-rich as they grew. The panda responded by switching to the leaves. The researchers found that about half of the calories the pandas ate were in the form of protein.
"They can know exactly where to go, and when to go, so they can get the most of the nutrients that their ecosystem can provide," said Silvia Pineda - Munoz, who was not involved in the study.
The work also shows that classifying an animals as herbivore or carnivore is more complex than one might sassume. "It's not whether you're eating plants but what of the plants you're eating," said Pineda - Munoz.
