East Island, the second largest island in the Paracel Islands on the mainland, has an area of 1.55 square kilometers, and the island is inhabited by primitive jungle and more than a dozen species of birds. What's even more special is that there are more than 400 bison living here.
It should be known that the East Island is an island composed of rising reefs and coral shell sand, which is not separated from the land, and the island has floated and sunk 3 times in 5,000 years, which also means that this group of bison has not evolved independently from the island, but is an outsider.
Obviously, bison can't swim here, so they must have been brought by people.
In 2003, mainland scientists came to the East Island to study the bison population, and during the investigation, a pond was found on the East Island, which stored fresh water and reached a depth of up to 1 meter during the rainy season, which is the source of life on which the cattle on the island depend.
After drinking water in the pond, the cattle will defecate here, and over time, a thick sedimentary layer has formed in the pond. Scientists collected sedimentary columns from the sedimentary layers of the ponds.
The study found that 1300 years ago, the pond was still located below the sea surface, followed by a deep layer of guano sediments, until 350 ± 40 years ago, when the sediment of cow dung appeared.
This means that the first bison that came to the East Island should have lived around 1653, at this time in the late Ming and early Qing dynasties, the mainland social unrest, these people are likely to be to escape the war with livestock to come here to survive, and when the war stopped, humans left the island, but the bison on the island stayed here.
For more than 300 years, the island's bison have been thriving and have lived until now, with a population of more than 400 at its peak.
On the other hand, however, the population of bison carried by humans when fleeing is bound to be not too large, and the east island is not large, which means that these cattle must have inbreeding in the process of breeding.
or there is a backoff
Inbreeding leads to lower viability and adaptability of offspring, which will affect the sustainable development of the population, so wild animals have evolved strategies to avoid inbreeding when living in the wild.
For example, male tigers will leave home when they reach adulthood and go far away to establish their own territory, Wandashan No. 1 is a male tiger that has just left his mother, and he mistakenly enters the village in order to establish a territory farther away from his mother; while the female tiger is more clingy to her mother when she becomes an adult, sometimes establishing a territory next to her mother.
Juvenile male lions will also voluntarily leave their own population and wander alone or join other populations, while females will stay in their original families, thus ensuring that they do not have relationships with close relatives.
Bison will also avoid inbreeding, generally males will form bachelor groups, while females and cubs will live together, forming a large group, and when it comes to mating, the males will rob the females of mating rights and occupy several females at the same time.
However, the original population of East Island bison is too small, and no foreign individual can improve the genes, which means that the bison on the archipelago are prone to inbreeding, and even the possibility of backcropping is not ruled out.
This has been repeatedly staged in many closed environments for wild populations, such as: lions living in the Ngorongoro Crater suffer from inbreeding severely, because of the inconvenience of communication with the outside world, resulting in the place becoming a "besieged city", it is difficult for foreign lions to enter it, and even if they enter, it is difficult to integrate into the lion group.
Although there is plenty of food here, the quality of the lion group is not high, the reason is that inbreeding is serious, a male lion has to mate with his mother, daughter, sister, etc., which also leads to the lion group living here is very close to the blood relationship, the ability to resist environmental changes is getting weaker and weaker, and it is easy to become extinct.
Wolves on Royal Island, Michigan, USA, are also extinct due to extreme inbreeding, and the last male and female wolves on Royal Island are so close that they are frighteningly close: they are both father and daughter, as well as "brothers and sisters" born to the same mother.
The bison on the East Island, in the process of independent life for more than 300 years, must also inevitably undergo inbreeding and even backcrossing due to the initial population shortage.
This also caused these bison individuals to be short, thin, and physically weak, and they would naturally become extinct without human intervention.
However, in the 50s of the last century, when the Xisha garrison was stationed, this group of bison was discovered, because the bison population was weak, so several strong bison were transported from Hainan Island, which improved the genes of the East Island bison, making the offspring stronger and continuing their survival, so that they could later reproduce to more than 400.
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