Giant Pandas: Carnivores, Bamboo-Eaters, and Things in Between

The giant panda — the rarest member of the bear family, a charismatic global symbol of conservation, and one of China’s most successful global brands — eats bamboo all day long, but has the digestive system of a carnivore. Giant pandas are, indeed, taxonomically classified as carnivores. Their ancestors were omnivorous and, about 7 million years ago, started to develop an interest in bamboo. The estimate is that they switched to an almost exclusive bamboo diet 2.4 million to 2 million years ago while, at the same time, developing strong jaws, and a pseudothumb that makes them not only expert grinders and kneaders with their mouths, but also skillful bamboo handlers.

Giant pandas

Photo credit: gill_penney, CC BY 2.0

Giant pandas eat different bamboo types and different plant parts (leaves, stems and shoots) at different times of the year — leaves and stems all year long, and fresh, soft bamboo shoots in spring and summer. However, they consume large quantities of bamboo every day, up to fifty pounds — or even more. Because pandas lack the long intestinal tract characteristic of other herbivores, researchers wanted to understand how these bears digest bamboo cellulose — the main constituent of the plant cell walls and vegetable fibers — and how they extract nutrients from it. Now, results from a new study show that, in giant pandas, the gut microbiome — the trillions of microorganisms that help with digestion (among other functions) — is optimized for meat consumption.

To study the panda’s gut microbiome, researchers in China sequenced ribosomal RNA in 121 poop samples collected from 45 captive individuals of different ages, at different times — spring, summer, and late autumn — over the course of a year. Then, they compared the microbes found in pandas with those found in other mammals — herbivores, omnivores, and phylogenetically related carnivores.

The researchers found that the giant panda gut microbiota is low in diversity, and highly variable across seasons. None of the cellulose-degrading bacteria typically seen in other plant-eaters were present in panda guts. Instead, the microbiome consisted mostly of Escherichia, Shigella and Streptococcus bacteria, which are normally found in carnivores.

Zhihe Zhang, director of the Chengdu Research Base of Giant Panda Breeding and lead study author, said in a press release: “Unlike other plant-eating animals that have successfully evolved anatomically specialized digestive systems to efficiently deconstruct fibrous plant matter, the giant panda still retains a gastrointestinal tract typical of carnivores. The animals also do not have the genes for plant-digesting enzymes in their own genome. This combined scenario may have increased their risk for extinction.”

According to the Conservation Biological Institute of the Smithsonian National Zoological Park, giant pandas live in a few mountain ranges in central China, in Sichuan, Shaanxi, and Gansu provinces. They once lived in lowland areas, but farming, forest clearing, and other development now restrict giant pandas to the mountains. There are only about 1,600 giant pandas left in the wild, while more than 300 live in zoos and breeding centers around the world, mostly in China.

Jonathan Eisen, a microbial ecologist at the University of California, Davis, told Nature that some of the microbes in the panda gut might still be highly efficient at breaking down cellulose. The study’s authors examined only microbial composition, not function. He said that microbes can change function rapidly, making it hard to predict how the microbiome may perform.

Indeed, results from a study published in 2011 showed presence, in panda guts, of microbes able to digest cellulose and break it down into simple sugars. The researchers that carried out the 2011 study thought that, in combination with adaptations related to feeding, physiology, and morphology, giant pandas could have evolved a number of traits to overcome the anatomical and physiological challenge of digesting a diet high in fibrous matter.

Zhihe Zhang and his collaborators are planning a follow-up study combining different scientific techniques to more fully understand the function of the panda’s gut microbiota on the animals’ nutrition and health.

9 comments

  1. So throughout this article, the fact that Giant Pandas lack the microbial life in their digestive tract that is considered important for cellulose digestion. Though they lack this adaptation to survive on their generally bamboo filled diet, they seem to be countering it just through massive amounts of bamboo consumption. The average Giant Panda weighs 100-115 kilograms, and on average they are eating 23 or more kilograms of bamboo a day. Compare this to .270 kilogram horse which only has to eat about about 7 kilograms of hay a day The Giant Pandas are eating almost a quarter of their body weight in bamboo to survive, while horses are eating only about 2.6% of their body weight daily.
    What I’m trying to say here is that they have survived for 2.4 million years feeding mainly on bamboo, so the lack of cellulose digesting microbes probably is not a big deal for the pandas, and that they might have even other ways of nutrient absorption from the bamboo we do not know about.

    • The Bamboo is probably not being absorbed in other ways by the Giant Pandas if they lack the microbiota to break it down, but rather they might be consuming such large amounts because they in fact cannot absorb many nutrients from the bamboo and need more of the bamboo to suffice their daily nutrient needs. Something I wonder though is whether or not bamboo has a slightly different composition from other plants that allow it to be broken down by the microbiota typically reserved for breaking down meats. Since the Giant Pandas only eat the shoots in the summer and spring time, is there a difference in content that would cause them to not eat the shoots in the fall and winter? Or simply a lack of ripeness so to speak?

    • I do not think that pandas need to consume a larger percentage of their body weight in food compared to horses because they are not efficient in breaking down and digesting cellulose. I believe that the reason why they need to consume such a large amount is because of the nature of the bamboo itself. Compared the natural diet of horses, the natural diet of pandas, which is bamboo, has much higher cellulose content and is less nutrient dense.
      I also think that there should be more studies done because the two studies in the article contradict each other. My understanding is that first study, they did not find the microbes present in other herbivores in the gut flora of pandas, but in the second study, they discovered that the gut flora of pandas are able to break down the cellulose. Anyways, I don’t think people should put the blame of decrease in panda population on the inefficiency of how pandas get their nutrients. Instead, they should blame themselves for destroying the natural habitats of pandas and the forest in which bamboos grow.

  2. Hopefully this gets linked onto OtterLyfe’s comment.
    Bamboo shoots are the new sprouting apical meristem of bamboo, so from them they will grow a new bamboo tree will grow. The Giant Pandas only eat them in the spring and summer because that’s really the only time of the year they are available. Once fall and winter set in the bamboo will stop sending shoots out from their rhizomes because it really isn’t a wise use of their energy once the weather turns colder and the days start growing shorter. Also bamboo shoots are actually relatively relatively nutritious and a popular food item in Asia. The fact that humans can eat them, of course we do cook them generally, means that the Giant Pandas should be getting the same amount of nutrients that we do from them. Because both humans and pandas are not capable of digesting cellulose.
    Also on the topic of Bamboo maybe being different in composition than other plants, that is probably not the case. If anything Bamboo might be even tougher because of it’s sturdy fibrous nature. It is used as building material very often in Asia, valued for it’s strength and toughness.

    • Your argument stating that humans and pandas get the same nutritional value out of bamboo is invalid. You are right per say that the value they get out of the shoot my theoretically be the same (however, the enzymes within the humans and pandas stomach may be different, causing digestion between the two to be different as well), but humans supplement their diet with a vast variety of other food that provides the large remainder of the nutritional value that we need. In comparison, the panda get ALL of their nutritional value from bamboo since they switched to an all bamboo diet. So if bamboo only gives 1% of the nutritional value per shoot, it doesn’t matter that humans get the same amount. They have other options. Instead, pandas need 100 of those bamboo to get their 100% nutritional value. While the panda might have a harder time to break down the cellulose to attain the most nutritional value and must eat more, or the bamboo doesn’t provide much nutritional value from the get go, it still overlooks the important point that pandas are optimized for meat consumption and their diet is that of bamboo (despite the fact that they might have microbiota that is efficient in breaking down cellulose).

    • I agree with your idea that Giant pandas are consuming less bamboo quantity since they are classified as carnivores may not be an issue to their health. Although, I think that in order to prolong the lives of giant pandas, we need to learn the type of the food that Panda prefer can help to determine the nutritional supplements that support their diet of bamboo in an effort to keep this rare animal endangered.

  3. Even though the amount of the microbes present in the gut of the panda are less in numbers when compared to other herbivores, these microorganisms are still able to be effective in dismantling the protein, fat and sucrose into their smaller component .Sometimes the consumed sugar canes are stiff so they are not digested completely and they are passed thru the digestive tract of pandas. Maybe pandas gastrointestinal tract will be adapted to the type of food they have been ingesting and more microbes will occupy their guts since living beings usually during their growth and development face consecutive environmental challenges, so they have adapt to a certain behavioral and molecular pattern based on the environment they are surrounded with.

  4. Giant Panda, they play really important part in the bamboo forests by transporting seeds in the forest and help in the vegetation growth. The most interesting trait of panda is their protruding wrist bone which help in holding of bamboo.
    WWF is an organization which is helping in the conservation of pandas .This organization was invented by china and help in maintaining the population of the giant panda, as these species play a very crucial role as they attract tourist.
    Currently Giant panda have been categorize in the endangered red list of the IUCN’s the main reason behind their extinction is the destruction of their habitat due the development.
    How can we save pandas? There are many ways on WWF site where we can contribute in saving pandas like donation or reducing the impact of tourism on panda, spreading about WWF among family and friends

  5. Pandas have found a strong niche within their bamboo forest. I don’t believe adults to have any natural predators, which is very beneficial considering their energy source and lifestyle habits. Seriously have you been to the zoo? They sit and eat, and look cute of course. This is not an easy lot in life to stumble in to. Other lethargic mammals like those in the sloth family can be so putrid and host so many microorganisms and critters that it serves as a defense to any would-be predators. Which makes me genuinely curious as to what would cause a shift of diet in this Ursidae from omnivore to herbivore. The post stating this occurred 20 million years ago doesn’t help much, what could have happened at that point in time to warrant a shift? A few ideas: exctinction of main prey group, competition from other predators, mutation towards plant digesting enzymes (unlikely), even possibly a change with the bamboo, which is also unlikely as Bamboo makes up nearly 1500 species and is global. Twenty million years on an evolutionary scale is very little. It could be worth considering mutation or some sort of migration within the natural gut flora of the pandas, but this study doesn’t make this possibility seem so promising. I’d like to see a panda’s response when presented omnivorous treats, like fish and bamboo. Would it choose the bamboo over it? Its very rare you see evolution working counterintuitively to an organism’s survival.

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>