This text number is 4316 and the estimated reading time is 6 minutes.
Reading enriches people and sharing makes people happy. At the end of the article, a mind map is attached to help you sort out the essence of the context in the text. Welcome to read, you are one step closer to knowledge.
The book shared today is The Law of Life.
Written by Sean M. B. Carroll, a member of the National Academy of Sciences, a fellow of the American Academy of Arts and Sciences, a professor of molecular biology and genetics at the University of Wisconsin, and a recipient of the Franklin Prize in Life Sciences. A science master with the same name as Edward Wilson, Oliver Sachs and Richard Dawkins, the winner of the Lewis Thomas Prize for Scientific Writing. Howard Hughes Medical Institute Science Filmmaker, whose science shorts and educational materials are freely available to thousands of students.
Carroll discovered that the distinction between microscopic and macroscopic living systems was only superficial, and that their essential laws were the same, so he wrote the book for inspiration and summarized the laws that apply to any ecosystem on Earth, the "Serengeti Law." This book tells us that behind the complex phenomena of life, there are only two words of law - "steady state".
<h1>01, what is the law of life
</h1>
Living systems are divided into different levels, the lowest level of living systems are cells, and the higher they go, the more complex they are, in order, tissues, organs, individuals, populations, communities, ecosystems, and biospheres. Different levels of life systems often give us completely different impressions, and the author believes that all life systems in the world, regardless of size, are subject to the same law, that is, the "law of life", and all life forms are stable. This steady state ensures that the living body remains intact when it is hit by a huge external force, and does not face the fate of being damaged, dismembered or even destroyed.
For example, under normal conditions, the pH of human blood is constant, the pH is stable at about 7.4, and the phH of 7.4 is steady state. If it is lowered to 6.95, the person will be unconscious or even die, and if it rises to 7.7, the person will have convulsions and epilepsy. We are usually healthy and healthy, neither comatose nor convulsive, because the human body relies on the nervous system and the endocrine system to automatically carry out various reactions, and is trying to maintain a stable phH of the blood.
All levels of life systems, whether it is the microscopic level in the organism, the mesoscopic level of the biological individual or the macroscopic level of the earth's ecology, their operation must follow the laws of life and cannot be separated from the regulation of steady state. This book summarizes a law that applies to ecosystems at all levels and finds their common logic, which can give us a more comprehensive grasp of the entire discipline of biology.
Now we can see that the core of the law of life is homeostasis, so how does the living system usually maintain homeostasis? The authors summarize the mechanism of maintaining homeostasis into four modes of regulation, namely positive regulation, negative regulation, double negative regulation, and negative feedback regulation.
1. Forward adjustment
Forward adjustment says that one parameter A changes, which causes another parameter B to change in the same direction. For example, the larger the number of grass on the grassland will promote the increase in the number of sheep, and here the grass is a positive adjustment to the sheep.
2. Negative adjustment
Negative regulation is the direction of adjustment in reverse, for example, the number of wolves will lead to a decrease in the number of sheep.
3. Double negative adjustment
Double negative adjustment is said to be the parameter A negative direction adjustment B, B and negative adjustment C, just like the number of wolves is more, the sheep will be reduced, the sheep will further promote the grass to become more, the wolf to the grass is the double negative adjustment.
4. Negative feedback adjustment
Negative feedback adjustment, A positive adjustment B, B too much will in turn inhibit A, just like the grass on the grassland makes the number of sheep more, but if the sheep become too much, they will eat the grass in turn, and the sheep to the grass is negative feedback adjustment.
These four modes of regulation maintain the homeostasis of all living systems all the time, not only sheep and grass, but also various cells and molecules in the human body, and large to the earth's biosphere, and they also maintain their homeostasis through these four modes of regulation. In most cases, this steady-state maintenance mechanism can work well, but if there are special circumstances and the steady-state is destroyed, various problems will arise. So what to do? That is to restore homeostasis.
For example, the American physiologist Walter Cannon, when he treated the wounded on the battlefield of World War I, found that the concentration of carbonate ions in the blood of shock patients was lower than normal, which indicated that the patient's blood was more acidic than the theoretical value, and the more acidic the blood, the lower the blood pressure, and the more serious the shock symptoms. Before Cannon, people couldn't treat severe shock, and once the patient's blood pressure dropped to fifty or sixty millimeters of mercury, it was basically unsaved.
But Cannon found an effective method, very simple, shock patients since the blood carbonate concentration is low, then give the patient a direct injection of sodium carbonate, sodium carbonate is alkaline, can improve the phH of the blood, Cannon through this method, forcibly restore the normal homeostasis in the patient's body, the effect is surprisingly good. Not long after, this treatment became the standard in the medical community, saving the lives of countless shock patients.
<h1>02, what is the Serengeti Law
The authors summarize a series of laws that explain the laws of macro-ecosystem operation, the Serengeti Law. What is the Serengeti Law? The name Serengeti comes from the Serengeti savannah on the border of Tanzania and Kenya in Africa. The author was originally a molecular biologist, but a trip to the Serengeti savannah shook him and gave him the inspiration to discover the laws of ecosystem operation. In honor of this, Carroll named the series of six laws the Serengeti Law. And it works in any ecosystem around the world. Let's look at these laws separately.
1. The law of key species
Beings are not equal, and the impact of "key species" is even greater. Certain species have a significant impact on the stability and diversity of their biomes, and the degree of influence often does not match their biological numbers. The importance of key species is reflected in the extent of their impact, not the level at which they are in the food chain.
2. The law of influence
Key species have significant indirect effects on species at the lower trophic levels in the food chain through the "domino effect". Some species on the food web can have important top-down impacts, often to a degree that does not match their absolute numbers, and this effect can affect entire biomes and indirectly affect species at the low trophic level.
Who determines the number of a creature? Original ecologists have long believed that the number of organisms in a species is generally determined by organisms lower in the food chain. The level of the food chain depends on the predatory relationship, the predator is at the high level, and the predator is one level lower, such as the wolf is the high level, and the sheep is the low level. The number of low-level creatures can determine the number of high-level creatures, but when you think about it, it seems that this is not the case, for example, wolves on the grassland generally do not eat all the sheep, and the sheep are not eaten, and the number of wolves is stabilized. This shows that the number of higher-level organisms here is not determined by lower-level organisms. So what factors determine it? Let's look at an experiment to understand these two laws.
The American biologist Robert Paine once did an experiment in which he found a reef by the sea that had no traces of human activity. There is a miniature ecosystem on this reef with marine life such as starfish, snails, mussels, barnacles and seaweeds, of which starfish and snails are predators on the reef, barnacles, mussels and other creatures are its delicacies, and mussels and barnacles feed on seaweed. Paine's approach is to remove observation, which is to pry up the starfish on the reef and throw them into the sea, remove the predator, and see what happens next.
The results of the experiment were unexpected, less than a year after the removal of predators, the predators did not get better, but disappeared in large numbers, and the population abundance on the reef dropped from 15 to 8 species; after 5 years of the experiment, all the space on the reef was occupied by mussels, and all other creatures disappeared.
That is to say, it turns out that on this reef, starfish is not the oppressor of most creatures, but the savior, which maintains the balance of the whole system by controlling the number of mussels. This experiment proved that predators can regulate the number of other species from top to bottom in the food web. Snails are also predators, but the presence of snails does not inhibit the expansion of mussels, only starfish.
3. The law of competition
Competition for common resources has led to population declines for some species. In competition for common resources such as space, food, and habitat, dominant species lead to population reductions in other species.
Scientists, for example, have been paying close attention to the number of organisms in the Serengeti steppe, and in the course of historical statistics, they found that from 1961 onwards, with the gradual disappearance of the rinderpest virus, the mortality rate of wildebeest and buffalo fell sharply, followed by a sudden surge in their numbers. Buffalo had only 16,000 in 1961, grew to 37,000 four years later and more than 58,000 after 11 years; wildebeest grew even more pronounced, from more than 200,000 in 1961 to 770,000 12 years later, to 1.4 million 16 years later. The rapid growth of wildebeest and buffalo populations has also affected many other species of organisms.
They graze, so the amount of grass in the Serengeti grassland is greatly reduced, the original grass can grow to 50-70 cm, and then it can only grow to 10 cm, the shorter grass allows sunlight and nutrients to benefit other kinds of herbaceous plants, which have spawned more kinds of butterfly communities; at the same time, the number of grasshoppers living on grass has decreased sharply, from more than 40 to more than 10 species; Tang's gazelle and wildebeest have similar feeding habits, so the number of grasshoppers has also decreased significantly under competition. From 600,000 in 1973 to more than 300,000 in 1977.
We can see that in this case, the wildebeest is the dominant species, and its larger population brings greater competitive pressure, which eventually leads to a decrease in the number of species as small as grasshoppers and as large as Tang's gazelles.
4. The law of massing
The size of the head affects the mode of adjustment. The size of an animal determines the mechanism by which its population is regulated in the food web. Small animals are regulated by predators (top-down), while larger animals are regulated by the food supply (bottom-up).
For example, the top predators in the savannah are lions, but even lions don't dare to act rashly in the face of hippos, rhinos and elephants weighing several tons. The researchers found a strong correlation between the size of an adult animal on the grassland and its probability of being preyed upon, with 150 kilograms being a clear dividing line.
Species weighing less than 150 kg are basically controlled by predators, while large animals over 150 kg are rarely affected by predators. For example, pygmy antelope weighing 18 kilograms and horned wildebeest weighing 120 kilograms have mostly lost their predators. But for large animals, such as buffalo, they are difficult to prey on by predators. As for giant animals such as giraffes, rhinos, hippos and elephants, the probability of being eaten as an adult is basically zero.
The size of animals determines the mechanism by which their population size is regulated in the food web, with small animals being regulated from the top down by predators and large animals being regulated from the bottom up by food supplies. That is, the number of small animals depends on the number of predators, while the number of large animals depends on the amount of food.
5. The law of density
Some species rely on their own density for regulation. The number of some animal populations is regulated by density constraints that tend to stabilize population size.
For example, wildebeests, a particularly large number of creatures, self-regulate. By analyzing the relationship between the population density and growth rate of wildebeests, the researchers found that when the population density is small, the growth rate is relatively high, and conversely, when the population density is large, the growth rate will become lower, which eventually leads to negative growth rate. There are many reasons for this, such as the competition among the masses has become more intense, infectious diseases have become more frequent, and so on. That is to say, the growth rate of the population number will be limited by the density of its own population.
This is actually the law of density, that is, the population of some animals is regulated by density constraints, which have a tendency to stabilize the population size.
6. The law of migration
Migration leads to an increase in the number of animals. Migratory behavior increases the number of species by increasing the availability of food (reducing bottom-up regulation) and reducing the probability of preyation (reducing top-down regulation).
Earlier, when we talked about the law of competition, we said that after the rapid growth of wildebeest and buffalo, the number of wildebeests reached 770,000, while the number of buffalo was only about 60,000, and the number of the two was more than ten times different. So is there any special reason for this? One reason is that buffalo is larger, but the more important reason is that buffalo doesn't have the kind of migratory behavior of wildebeest.
Migration is essentially a watery grass, which can solve the problem of food shortages, and because predators have to feed their cubs, they are often unable to migrate, so migration can also bring safety to wildebeest.
Final words:
In the Serengeti steppe, the status of animals is not equal, and the role of key species is important, and their effects extend down to more nutritional levels. Species of the same level of nutrition also compete with each other for survival.
However, regulation at the molecular level and in ecosystems follows the same universal logic – positive regulation, negative regulation, dual negative regulation, and feedback regulation mechanisms are ubiquitous. Only by abiding by the laws of life can we repair the damaged ecological environment and build a better home!