At this year's Beijing Winter Olympics, the giant panda showed its face again, which surprised people all over the world, and also led to "a dun is hard to find".
In the more than 10 years of studying giant pandas, I have found that although everyone loves giant pandas, some of the biological knowledge and conservation and management issues of giant pandas are still not very clear, and there are even some misunderstandings.
For example, in the seventies and eighties of the last century, there was an argument that the giant panda was bound to become extinct due to the continuous decline of the population, low genetic diversity, low reproductive ability, and the biological characteristics of eating bamboo, and they would go to the end of evolution, or the dead end of evolution. Even in recent years, this argument has been raised repeatedly. In 2009, BBC media personality Chris Packham wrote that we should let the giant panda die out so that more resources could be invested in other animals.
Today, I will discuss with you four questions: Is the population of the giant panda declining? Is its genetic diversity and reproductive ability low? Is the giant panda adaptable to bamboo?
How to count the number of giant pandas?
Completed: 10% //////////
First, let's take a look at the giant panda population. When it comes to population size, the actual question is how many giant pandas there are, and this is what many people ask me.
▲ Everyone thinks ......
So how do we survey the giant panda population? It's not something we can just look at and count in the wild. Giant pandas live in the mountains and are also known as "bamboo hermits", which are actually difficult to see in the wild. In fact, it depends mainly on a special secretion of giant pandas: poop.
▲ Practical ......
The picture above shows a giant panda with a ball of fresh bamboo shoot dung. We can see that the giant panda's feces contain the remnants of chewing and digesting, which we call "bite joints". The length of the bite joint is related to age: the age of the bite joint is long, and the age of the bite node is short. Combined with the distance between the stools, the individual can be identified.
For example, when the distance between two clumps of feces in the wild is greater than 1.5 km, it can be directly judged as two individuals, and if the distance between them is less than 1.5 km, but the difference in the length of the bite joint is more than 2 mm, it can also be judged as two individuals. This is all based on a large number of statistics.
Based on this principle, the mainland has carried out four national giant panda surveys, once every 10 years. Probably no other species in the world has received so much attention and invested so much human, financial and material resources in so many investigations.
The first survey was conducted in the 70s and found 2,459 pandas, and the second was in the 80s with 1,114 pandas. We found that the giant panda population had plummeted by nearly half, and it was then that the population began to decline. There was a lot of pessimism about the fate of the pandas, because of the massive deforestation that took place at the time.
▲ Results of the Fourth National Giant Panda Survey, a total of 1,864 pandas (2015)
But we see that the results of the third and fourth giant panda surveys are 1,596 and 1,864 respectively. 1864 is the latest survey and shows that its population is constantly growing. What's going on here?
After the Yangtze River flood in 1998, a ban on logging of natural forests began to be implemented across the country. The forest ecosystem in the southwest of our country has been well protected, and the habitat of the giant panda has gradually recovered, so the population has naturally begun to grow.
You may also wonder: Those poops that are less than 1.5 kilometers away and have a bite length of less than 2 millimeters must be a giant panda? This problem does exist, which shows that the results of the mainland giant panda population survey are still a very conservative estimate.
In order to investigate the population more accurately, our team further developed a molecular fecal method – again through the poop of giant pandas.
▲ Molecular fetological survey methods
Fresh panda poop has a layer of white mucus on the outside, which is left behind by the secretion of mucus from the panda's intestines, which is rich in intestinal exfoliated cells. We can extract the panda's DNA from these cells to identify individuals. This is similar to a forensic doctor searching for a suspect's blood or hair at a crime scene for individual identification.
▲ Left: The number of giant pandas in Wang Lang Reserve
右:Zhan XJ... Wei FW. Curr. Biol. 2006.
Using this method, we conducted a pilot survey in the Wanglang Nature Reserve in Sichuan. Through the analysis of 245 fresh feces, we identified 66 giant panda individuals, which is much higher than the 27 in the third giant panda survey, indicating that traditional survey methods greatly underestimate the number of giant pandas in the wild. Therefore, it is estimated that there should be more than 2,000 giant pandas in the wild, which also confirms that the current giant panda population is constantly growing.
We humans prohibit direct blood relatives and collateral blood relatives within three generations, because inbreeding leads to a decrease in genetic diversity: harmful genes have a higher probability of being homozygous and then come into play. Therefore, low genetic diversity is detrimental to the development of a population, and high genetic diversity represents higher evolutionary potential.
So, does the relatively small number of giant pandas mean that genetic diversity is also low?
In order to explore the genetic diversity of giant pandas, our team analyzed the genetic information of 159 wild giant pandas through long-term sample accumulation, and found that the genetic diversity of giant pandas is relatively high compared with other bears (such as polar bears and spectacled bears). This also shows that the giant panda still has a high evolutionary potential.
Are giant pandas "frigid"?
Completed: 30% //////////
The "evolutionary end theory" also argues that the reproductive capacity of giant pandas is very low. Is that so?
The argument that the giant panda has low reproductive ability mainly comes from the "trilemma" that appeared in the captive breeding of giant pandas in the eighties and nineties of the last century, that is, the difficulty of estrus, the difficulty of breeding and conception, and the difficulty of cub survival. So what's the situation like now?
At present, the captive breeding of giant pandas in mainland China has achieved great success, overcoming the problem of breeding trilemma. Taking the survival of cubs as an example, it was difficult for giant pandas in the wild to raise twins because they did not hibernate, and could only take one cub away when they were moving and foraging for food, and the other had to be abandoned. In a zoo, it is also not allowed to raise two cubs.
However, breeders have invented a method of rotational feeding of twins: every day, the mother panda feeds one cub, the other is raised in captivity, and then rotated to receive breastfeeding, which significantly improves the survival rate of captive giant panda cubs.
▲ Giant panda cubs bred at Chengdu Giant Panda Breeding Research Base
At present, captive giant panda breeding has shifted from emphasizing quantity to emphasizing quality. As of October 2021, there are 673 giant pandas in captivity on the mainland, and the current breeding goal is to maintain the genetic diversity of giant pandas in captivity as much as possible and avoid their inbreeding.
▲ Track wild giant pandas wearing GPS collars
You may be curious: captive giant pandas are very successful, but what about wild giant pandas? Our team put GPS collars on the wild giant pandas in the Foping Nature Reserve in Qinling, Shaanxi Province, and followed them for a long time to observe their courtship, mating, calving, and child-rearing behaviors.
Through more than ten years of research, we have found that the breeding and child-rearing behaviors of giant pandas in the wild are very normal. During the breeding season, a female giant panda in heat will attract multiple male giant pandas to gather, so how do male giant pandas decide their mating priority?
▲ The upper left is the winner, and the rest are the losers
The image above shows four male pandas in the breeding farm, who have to fight to determine their mating priorities. One of them won, the other three failed, and two of them had scars on their faces, indicating that they had fought fiercely. We've also found that in the wild, it's usually the big, strong ones who win the game. Scars like the giant panda's face have actually become a basis for infrared camera methods to identify individual giant pandas.
▲ Courtship and mating of giant pandas
In more than 10 years of field research, we have observed dozens of giant panda breeding, and their courtship and mating behaviors are very normal.
▲ Giant pandas give birth and raise young
We also used infrared cameras to observe and study the calf and child-rearing behaviors of giant pandas, and found that giant pandas can give birth and raise young in the wild normally.
Giant pandas are in estrus in March and April every year, and female pandas are usually five months pregnant and start giving birth in August and September. As mentioned earlier, giant pandas usually only raise one cub because it does not hibernate. Unlike polar bears and brown bears, after the hibernation period, their cubs are actually grown up and can come out and walk on their own. But giant pandas are mainly raised by female pandas.
▲ Wild giant panda cubs
Usually when the cubs reach the age of one and a half or two-and-a-half, the mother panda will drive the cubs out of the house to set up their own doors. So we can occasionally see giant panda cubs living alone in the wild, and they are all healthy and normal.
Whether it is courtship, mating, giving birth to cubs, and raising young, the reproduction of wild giant pandas is very normal, so its reproductive ability is not low.
Do giant pandas that only eat bamboo live well?
Completed: 40% //////////
So let's look at the last argument of the "evolutionary end theory", which is that giant pandas cannot adapt to bamboo.
▲ Can giant pandas adapt to low-nutrient bamboo?
One of the "cuteness" of the giant panda is that it eats bamboo, which is not as ferocious as tigers and leopards that eat meat. But bamboo is a high-fiber and low-nutrient food, so how can giant pandas absorb enough nutrients to maintain its growth and development?
Our team's long-term research has found that giant pandas have adapted well in many ways.
Morphologically, the red arrow in the picture above shows a very special structure of the giant panda, known as the pseudo-thumb or sixth finger. It is formed by the expansion of a small bone on the side of the thumb, which is held opposite to the thumb and is able to grasp the bamboo with agility to assist in foraging. In such a large group as carnivores, only giant pandas and red pandas have pseudothumbs, and no other carnivores have such dexterous grasping ability.
Giant pandas have round and round brains that are very cute because they have well-developed masseter muscles attached to them, which are easy to chew bamboo. In addition, the molars of giant pandas are very large and flat, which is convenient for grinding bamboo. So morphologically, giant pandas have adapted well to eating bamboo.
Bamboo is not highly nutritious, so giant pandas are very picky about eating bamboo. In the wild, it selects the most nutritious species and parts of bamboo. But when there are bamboo shoots, it will eat bamboo shoots first, and when there are no bamboo shoots, it will eat bamboo leaves and bamboo poles. Bamboo leaves and bamboo poles are also selected from the annual ones that have just grown, which are very fresh, tender and nutritious. The kind of perennial, giant pandas basically don't eat it. In this way, pandas are able to get as much nutrition as possible in their limited feeding time.
In addition, giant pandas also have a series of strategies to save energy. Our team's research found that the daily energy expenditure rate of wild and captive giant pandas is very low, only 37% of its predicted size. This number is similar to that of a sloth and lower than that of a koala. And we know that sloths and koalas are two animals that move very slowly.
▲ No YG... Wei FW. Science, 2015.
In addition, the giant panda does not hibernate, so how can it maintain a constant body temperature in the cold winter? Through the infrared camera to measure the temperature of the giant panda's body surface, we found that the thick fur on the body surface of the giant panda can maintain a constant temperature, compared with dogs and cows without thick fur, its body surface temperature is very low.
In terms of activities, giant pandas also have different strategies. Searching for panda droppings and feeding in the wild has revealed that they are mainly found in some wide habitats and gentle slopes, while they are difficult to find on steep slopes, dense bamboo forests and shrubs. It's actually a way for pandas to conserve energy.
In addition, another cuteness of giant pandas is that they are "lazy". As everyone should know, it is slow, and it is true in the wild. Through GPS collar tracking in the wild, it will be found that the giant panda moves a very short distance, moving less than 500 meters per day on average, and spends 50% of the time resting and the other 50% of the time for feeding, through this strategy, its energy consumption can be minimized.
▲ Zhu LF... Wei FW. PNAS, 2011.
Huang GP… Wei FW. Cell Reports, 2022.
Cellulose and hemicellulose are the main components of bamboo, but humans and other mammals are not able to digest cellulose and hemicellulose, because we mammals cannot synthesize cellulase, which mainly depends on the help of intestinal microbes. Studies have shown that in the intestinal microbes of giant pandas, there is a type of clostridium that can secrete cellulase, so as to digest cellulose and hemicellulose well, so as to provide nutrition, and there are also clostridium butyrate, which can secrete butyrate, thereby enhancing the anabolism of phospholipids for the needs of body development and growth. Therefore, microorganisms play a very important role in the nutritional utilization of giant pandas.
These studies show that giant pandas are actually very well adapted to bamboo.
The next question you may ask is: Giant pandas eat bamboo, if there is no bamboo, will they starve to death in the wild? Will this happen? This situation is possible. Because bamboo blooms, large-scale bamboo flowering and dying occasionally occur in the wild.
▲ Flowering bamboo forest
What kind of plant is bamboo? Actually, it's a plant of the grass family. When you think of grasses, you think of wheat and rice, right? Every year, they bloom, bear fruit, and eventually the whole plant dies. The same goes for bamboo, but fortunately, the flowering cycle of bamboo is 40-60 years, so it is actually difficult to see large-scale bamboo flowering in the wild. Even in winter, the bamboo is green and lush, and it can be eaten by giant pandas.
▲ Large-scale bamboo flowering recently
1974-1977: Minshan, 138 giant pandas died
1983-1988: Qionglai, 141 giant pandas died
But in the 70s and 80s of the last century, there were two large-scale bamboo blooms. One is in the Minshan Mountains in Sichuan, and the other is in the Qionglai Mountains. At that time, the peak of deforestation was particularly severe, and the habitat fragmentation was particularly severe, and the migration and spread of giant pandas may have been affected, resulting in the discovery of more than 100 giant panda carcasses in the wild.
▲ George Schaller: "The Last Panda" (1993)
Attention to the fate of the giant panda arose around the world, when renowned panda expert Dr. George Schaller wrote in his book The Last Panda that the effects of large-scale bamboo flowering, human poaching and habitat fragmentation made the panda more pessimistic. It was also at that time that the world began to invest heavily in the conservation of giant pandas.
Can giant pandas in the wild cope with large-scale bamboo flowering? Field studies at the time found that giant pandas responded to large-scale bamboo flowering in two ways: one was to migrate and spread to other areas, but if habitat fragmentation was severe, it could indeed affect the panda's migration and dispersal, and the other was to forage for other bamboo species. Large-scale bamboo flowering is usually the flowering of a certain type of bamboo, and in each of the six mountain systems where giant pandas are distributed, there are at least seven or more species of bamboo, so there are other bamboo species that can be foraged for giant pandas. From these two points, if there is no serious problem of habitat fragmentation, the giant panda can cope with the large-scale phenomenon of bamboo flowering and death.
So why are giant pandas endangered?
Completed: 60% //////////
The above four aspects show that there is nothing wrong with the giant panda in terms of biological characteristics. You may ask: So why are giant pandas endangered?
▲ The picture comes from the Internet
Giant pandas have an 8 million year history of evolution, and the oldest fossil was found in Yunnan, which is 8 million years old. During this 8 million years of evolution, animals such as the saber-toothed elephant, which once lived at the same time as the giant panda, have become extinct, while the giant panda has survived to this day. What happened in the meantime, and what caused it to become endangered?
Previously, it was difficult to reconstruct the evolutionary history of species on a long scale of 8 million years, and these fossil sites were scattered, making it difficult to reconstruct the population changes of giant pandas.
▲ Zhao SC... Wei FW. Nat. Genet. 2013.
Now, with the development of technology, it is possible to reconstruct the evolutionary history of a species over the past few million years through the analysis of genome-level variation. Our team reconstructed the 8 million years of evolutionary history of giant pandas by sequencing the giant panda genome.
You can see the two grooves in the chart above, which shows that the giant panda has experienced two drastic population declines in history. What is the reason for this? It is mainly caused by the penultimate glacial period and the last glacial period of the Pleistocene, that is, by paleoclimatic changes. Over the past 10,000 years, the giant panda population has been fragmented into several isolated geographic populations as human activity has increased dramatically.
That's why we say it's paleoclimate change and human activities that make the giant panda endangered, not that there's something wrong with its own biology.
Therefore, whether in terms of population size, genetic diversity, reproductive ability, adaptability to bamboo, or the factors that drive the endangerment of the giant panda, the giant panda is currently living a good life, and it has not reached the end of its evolution.
Do we need to continue to protect giant pandas today?
Completed: 80% //////////
In 2016, the International Union for Conservation of Nature (IUCN) downgraded the threat status of the giant panda from "endangered" to "vulnerable" based on the mainland's achievements in giant panda conservation, reflecting the remarkable achievements made by the mainland in protecting the giant panda.
But there is another voice, some people think that the giant panda is no longer an endangered species, and we no longer need to protect the giant panda, is that right? Surely not so, right? It is not easy for us to achieve conservation results, and we need to continue to protect and try to maintain their survival.
Giant pandas are also facing many threats, not least of which are habitat loss and fragmentation. At present, 1,864 wild giant pandas live in 33 isolated geographic populations, of which 22 populations have fewer than 30 individuals and 18 populations have fewer than 10 individuals. That said, although there are several large populations in the wild, there are many smaller populations, and the fate of these populations is very much worth our attention.
Secondly, cases of giant panda deaths caused by canine distemper, parasites and other diseases occur from time to time. Canine distemper is a viral disease that is contagious. At the end of 2014, canine distemper occurred at the Louguantai Captive Giant Panda Breeding Center in Shaanxi Province, which eventually led to the death of five giant pandas. There were only about 20 pandas in the first place, so it was a big hit on their panda population. Scientists are also stepping up research on a canine distemper vaccine for giant pandas.
In addition, new factors such as environmental pollution and global climate change are also affecting wild giant panda populations and habitats.
The establishment of the Giant Panda National Park was officially announced at the 15th Conference of the Parties to the United Nations Convention on Biological Diversity in 2021. The Giant Panda National Park can protect the previously scattered giant panda reserves as a whole, including areas that were not previously protected areas, so as to better solve the problem of habitat fragmentation.
The establishment of the Giant Panda National Park not only protects the giant panda, but also protects more than 8,000 species of wild animals and plants distributed in the same area as the giant panda, and protects the forest ecosystem in southwest China, which is also an ecological barrier in the upper reaches of the Yangtze River. Therefore, the establishment of the Giant Panda National Park is of great significance, which not only enables the giant panda to play the role of a flagship species or a star species, but also plays the role of an umbrella species, and holds up a safety umbrella for other species.
Finally, I would like to share a question that everyone is very concerned about: what is the significance of protecting giant pandas and their habitats, or what is the significance of protecting wild animals, or even what is the significance of protecting biodiversity?
In the past, we did not have a quantitative indicator, we would say that any animal is a link in the food chain of nature, a link in the food web, a link in the ecosystem, if it is missing, the food chain and the food web will not be complete, the ecosystem will be out of balance, and there will be many problems.
Now an international team led by our team has conducted an in-depth assessment of the value of the ecological services of the giant panda and its habitat, which consists of three main services. The first is the provision of services, where a good ecosystem can provide us with food, clean water, the second is the regulation of the atmosphere, the water cycle, soil quality, floods, and even the probability of wildlife diseases, and the last is cultural services. The adorable giant pandas and beautiful habitats make people willing to pay for tickets to see them.
Taken together, these three services add $2.6 billion to $6.9 billion worth of ecosystem services to giant pandas each year, 10-27 times the amount invested in giant panda conservation. This fully shows that the protection of giant pandas and their habitats is very worthwhile. This also interprets the ecological concept of "lucid waters and lush mountains are invaluable assets", and it is very worthwhile for us to protect biodiversity.
In the past ten years of studying giant pandas, we have seen that the population and habitat conditions of giant pandas are constantly improving, and the probability of finding giant pandas in the wild is also getting higher and higher. The state is also constantly introducing new protection measures. Therefore, from a biological point of view and from the effectiveness of conservation and management, I believe that the giant panda will have a better tomorrow.