Why do hippos like to live in the water?
Hippo is very special. It is the only amphibious animal among ungulates. So why did hippos choose amphibious life? Why can't they leave the water for a long time?
Physiological reason: highly dependent on water
First of all, hippos must drink plenty of water. A significant difference between the hippo's digestive tract and other artiodactyls including ruminants, pigs, camels is that the colon is short and there is no cecum. This section is responsible for absorbing water. This leads to the absorption of water.The hippo's absorption efficiency of water is particularly low. The fecal water content is more than 90%. It must drink a lot of water to meet the body's demand for water, otherwise it will become dehydrated.
Secondly, the hippo's skin is delicate and easily burned or cracked under the sun. In order to adapt to aquatic life, the hippo's skin has been improved accordingly. The whole body is smooth and hairless to reduce the resistance to movement in the water.The disadvantage of this kind of skin is that it lacks protection and is sensitive to sunlight, especially in tropical Africa. The sun is so poisonous. Therefore, hippos need to be soaked in water to keep their skin moist and never dare to leave the water source for too long.
When the hippo stays away from the water for a long time, a red liquid called “sweat” is secreted on the surface of the skin. In fact, this liquid is neither sweat nor blood. It is red because it contains acid.Pigment. Sweat and blood has a three-in-one function of sunscreen, moisturizer and antibiotics, which can protect the skin.
Again, the hippo metabolic rate is very low, which is suitable for a relatively small circle of life. The hippo has a low metabolic rate, generally speaking, it eats less and does not like to move. For comparison, hippos eat 5 hours a day, while white rhinos eat daily.12 hours. A 1.3-ton hippo eats 13 kilograms of forage per day, while a white rhino of the same weight requires 26 kilograms of forage per day.
This is mainly because the hippo's digestive tract structure is special. Hippo's big teeth are useless for grazing and will be a hindrance. When the mouth is closed, the upper and lower canine teeth are locked to each other and cannot be chewed sideways, chewing efficiencyIt is abnormally low. Like other cloven-hoofed animals, the hippo depends on the symbiotic digestive flora in the forelimb to digest plants, and because of its poor chewing ability, as a compensation, its microbial activity in the forelimb is stronger.
Hippo chewing is not efficient. It is not feasible to increase food intake to obtain more energy. Symbiotic microorganisms take some time to process food. Eating too much will only cause food to pass through the digestive tract too quickly and reduce digestion efficiency.So the hippopotamus simply eats less and digests well. It lives in the water and eats grasses near the water. Water and food are close to each other and can be obtained without taking too much distance. This can save energy to the maximum.
Evolutionary reasons: semi-aquatic ancestors
Hippos have traditionally been classified as artiodactyls, but modern molecular biology research has found that their closest relatives are actually whales and dolphins. Therefore, some scholars have advocated the merger of cetaceans and artiodactyls, called cetaceans.Four suborders, with the exception of the whale-hippo suborder, the other three suborders in descending order of kinship with hippos are: ruminant suborder cow, sheep, and deer, pig suborder and lame suborder.camel.
Hippo's prehistoric close relative: The charcoal beast
The common ancestor of whale and hippo has been different from other artiodactyls for a long time. Their common ancestor was semi-aquatic and appeared 60 million years ago. Since then, hippos have not left the water, so its semi-aquaticHabit is inherited from ancestors. About 54 million years ago, primitive whale-hippo-type animals were divided into two branches, one was a whale and a dolphin, and the other was a charcoal beast and a hippopotamus. By the Pliocene 2.6 million years agoAt the end, all the charcoal beasts became extinct, leaving only hippos to survive solitary.
Hippo has many characteristics to adapt to aquatic life. First of all, it has a thick skin and can insulate. The thickest part of a 1.4-ton hippo actually reaches 3.5 cm, which is very helpful for maintaining body temperature in the water. Second, Its nose, eyes and ears are all on the top of the head. When it is soaked in water, as long as the top of the head is exposed to the water, you can gain insight into the water environment.
Also, when the hippo dives, the ears and nostrils can be completely closed, and its air-holding ability is very strong. It only needs to emerge once every 5 minutes to change the air. Hippos can perform almost all life activities underwater. MatingAt that time, the female hippopotamus was completely submerged, the cub was born underwater, and breastfeeding could be done underwater. The hippopotamus could also sleep underwater and subconsciously surface to ventilate without waking up.
However, compared with its close relative, the whale, the hippo's ability to adapt to water is far behind. It doesn't swim at all, it can only use the foot of the river to jump forward in the water. Moreover, the hippoThe staple food is grass on the shore, not aquatic plants, which means that its diet cannot escape the restrictions of land, so experts call hippos semi-aquatic.
Behavioral reasons: Avoid the enemy
Hippos usually go ashore for food at night. There is no hot sunlight at night, but the hippopotamus still dare not leave the water for a long time because its biggest enemy lion is also active at night. Because the hippo is too large and stays in the water for a long timeHere, lions rarely kill hippos. For example, in the investigations in Serengeti, Kalahari, Manila, and Nairobi, lions have not been found to kill hippos. In Kruger, lions have only killed hippos.One thousandth of the total number of hunts is also only 1.4% in Kafu Park and Kafue River National Park.
During the dry season, hippos sometimes cannot get enough food from the shore, and may be up to 4 kilometers away from the bank. At this time, it is very troublesome if they encounter lions. Hippos are quite awkward on land. Once the power of the lions can stop themWhen it enters the water, the hippopotamus will quickly lose its resistance due to dehydration and lack of physical strength. It will be killed by the lion alive, especially the situation of the young hippo is more dangerous. Therefore, the hippopotamus does not dare to leave the water for a long time at night.
Hippos choose a semi-aquatic life to occupy an undeveloped niche. African herbivores are terrestrial, and there is only one hippo in fresh water. This is the mystery of the hippo's prosperity so far. However, it is highly dependent on water.It also limits the distribution and spread of hippos. Today hippos are only found in Africa, and they have been seen in Europe and Asia in history, but have never entered North America.
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