Liu Xiang of the Han Dynasty has this passage in his book "Saying The Garden": "There are trees in the garden, there are cicadas on it, cicadas dwell high and mourn, drink dew, do not know that the praying mantis is also behind it, the praying mantis is committed to the song to take the cicada, and do not know that the yellow finches are beside it." This is where the idiom "praying mantis catches cicadas, yellow finches are behind" comes from. Nowadays, it is often used as short-sighted, coveting small profits and not knowing the consequences.
Photo by Shanghai Entomological Museum
What is the food chain
In the ecological environment of nature, there is a kind of eating and being eaten between various organisms, which constitutes a food relationship of mutual dependence and coexistence. This interconnectedness of chains is what we call the "food chain" in ecosystems.
The "food chain" is also called the "nutrition chain". It is a nutrient relationship between various organisms in the ecosystem that are linked to food. For example, algae in ponds are food for water fleas, water fleas are food for fish, and fish are food for humans and water birds. As a result, algae --- faiths--- fish--- people or water birds form a complete food chain.
When this chain is further extended, that is, animal droppings and carcasses return to the soil, and the microorganisms in the soil break them down and become nutrients for plants, so that they grow new leaves and fruits, which provide food for insects, and insects become food for birds, and with birds, there are other predators. This reincarnation thus forms a healthy cycle in nature's ecosystem.
Schematic diagram of the food chain between organisms (from the network)
The term "food chain" was first coined by British animal ecologist Alton in 1927. The food chain usually has the following characteristics: 1. A food chain generally contains 3-5 links 2. The beginning of the food chain is usually green plants. 3. The second link in the food chain is herbivorous animals. 4. Organisms in the third or other links of the food chain are generally carnivores.
The "food chain" acts as a food pathway between organisms, which links different species in various populations in terms of biological populations. The food chain is transported between organisms through energy and nutrients, and has a one-way conduction and gradual decline. Because there are very few species in the food chain that contain more than six species (because the transfer efficiency between food chains is 10-20%, it cannot be extended indefinitely, there is a limit), so the energy or nutrients transferred will decrease a little whenever it passes through a stage or food level.
At that time, Darwin described such an interesting phenomenon in his book On the Origin of Species: Where there are many cats, sheep can raise a lot. What does this sheep have to do with cats? It turns out that sheep like to eat a plant called clover, and clover is bred by pollination by the marugami bee, but the voles prefer to eat the honey of this bee, which often destroys the honeycomb. So, the more voles there are, the fewer bees, and the fewer opportunities for clover pollination. Conversely, the more cats are raised, the fewer voles there are... The more marigold bees, the better the clover has a chance to get a better harvest, and the more clovers there are, the more sheep will naturally be fed. Therefore, the "cat, vole, pill flower bee, clover and sheep" constitute an interconnected and complete food chain. It can be seen that if a certain link here is destroyed, it will affect the living conditions of one or more animals and plants.
Composition of the food web
However, between the different organisms in the ecosystem, in fact, eating and being eaten is not as simple as the above food chain is expressed, insect-eating birds not only prey on beetles, but also prey on insects such as moths and butterflies, and insect-eating birds are not only hunted by falcons, but also predators by cats, and even bird eggs are often used as food for snakes, rodents or other animals.
Thus, there is a generally intricate connection between the various organisms in the ecosystem through the transmission of energy and nutrients, which is like an invisible web that spreads out, wrapping all living things in it, so that they have some direct or indirect connection with each other, thus further forming the concept of the so-called "food web".
Only a complex food web can keep the ecosystem stable, it is generally believed that the more complex the food web, the stronger the ability of the ecosystem to resist external interference, once the food web is simplified, the ecosystem is prone to fluctuations, and even to collapse.
Let's look at the following example: in the United States in 1870, there were about 4,000 deer living in the 467 square kilometers of the Kaiba Plateau, as well as a small number of cougars and wolves, and the local people hunted mountain lions and wolves for the safety of deer, and by 1924, these two types of carnivores were basically extinct in the local area, and the deer herd quickly multiplied to more than 100,000 heads. However, in the past two winters, the deer herd has plummeted to about 60,000 heads, and by 1939, there were only 10,000 or so deer left, so why did the deer herd that had lost its natural enemies plummet?
It is precisely because of the extinction of mountain lions and wolves that the deer population has increased dramatically out of control, and the grassland has become significantly insufficient due to the excessive nibbling of the deer herd, and the number of deer that has lost food has of course been greatly reduced. If there are other carnivores besides lions and wolves, then lions and wolves are wiped out, and these carnivores will inevitably increase their predation on deer, so as not to make the deer herd develop too fast, which may prevent the collapse of the ecosystem. Conversely, in addition to deer, there are other cattle or antelopes on the grassland, and if the deer are eaten out, the role of lions and wolves may not be too large, you say?
The role of ecological balance
An ecosystem, the number and proportion of various organisms can always be maintained in a relatively stable state, which has become the ecological balance that we vigorously advocate today.
In ecosystems with complex food webs, the extinction of any one organism has the potential to fluctuate the stability of the entire ecosystem to varying degrees until it triggers drastic changes in the ecosystem. Therefore, once the food network that constitutes the ecosystem and the type and number of species show a simplistic trend for various reasons, it is easy to cause the food chain to have missing links, which eventually leads to the imbalance of the ecosystem.
In the early 1970s, in the Hulunbuir Grassland in Inner Mongolia, planes were used to sow drugs to extinguish the raging rat plague, and the effect was indeed remarkable at first, and in a short period of time, the number of rats was greatly reduced. But the method of spreading poisonous bait has seriously polluted the grassland, and even the rat-eating eagles and the vermin-eating birds have all been poisoned, resulting in the spread of pests everywhere. The destruction of grasslands has become even more serious.
The weasels on the steppe whose main diet was rats also starved to death in large numbers because they could not find food. What is more serious is that due to the death of natural enemies of rats such as weasels and eagles, the remaining rats that escaped the disaster were able to recuperate, but they quickly multiplied and resumed a new round of competition with livestock. Sad people, because of the quick success of the rat eyes, tearing off the original complete food chain of the grassland, in the face of the unbalanced ecological environment, finally destroyed their beautiful home.
Many lessons to learn
In this world, the unexpected is also: the food chain circulation system, when disturbed by the superposition of certain additional factors, will also be involved in another vicious circle, for example: when the pesticide DDT is over-sprayed, in addition to playing a role in insecticidal, a part will be absorbed by the lower end of the food chain: grass, although the concentration is very low, will not affect the growth of grass, but rabbits eat these grasses, these toxic substances are difficult to be excreted by it, because they eat grass for a living, These toxic substances gradually accumulate and enrich in their bodies. When the eagle pounces on these rabbits, the toxic substances will also further accumulate and enrich in the eagle's body and reach a higher concentration. The national bird of the United States: the bald eagle, is the accumulation of excessive amounts of these toxic substances in the body, resulting in the eggshell of the eggs it lays too thin, making these eggs very easy to break before hatching, and endangering the breeding of the next generation, the amplification effect caused by the accumulation of this poison chain once made them close to the endangered situation....
Today, the environmental pollution caused by human production activities is also very serious for itself, and the incidents of interference in the human food chain are sometimes prominent. As mentioned above, animals and plants absorb nutrients from nature to grow, but while absorbing nutrients, they will also absorb certain toxic components from the polluted environment, and human beings, as a link at the end of the food chain on the earth, must face a dangerous situation when they are involved.
As a classic example, Japan's minamata disease caused by environmental pollution, that is, some organic chemical plants mercury-containing wastewater discharged to the sea, inorganic mercury is absorbed by some microorganisms in the seawater and converted into organic matter - methyl mercury, and the fish and shrimp shellfish in the sea, it is to swallow these methylmercury-containing microorganisms, it is invisibly absorbed and enriched methylmercury into the body, when humans eat these mercury-contaminated fish, shrimp and shellfish, methylmercury will then be transferred to the human body, When the gradual enrichment of these methylmercury reaches a higher concentration, it also damages the human nervous system, and finally leads to the tragedy caused by the environmental pollution of Minamata disease.
Having said so much, it also makes people think a lot, and the lesson of "praying mantis catching cicadas and yellow finches behind" from different angles in reality is happening all the time around us. This is not as simple as the old saying: "Make up for the dead, it is not too late". It can be seen that today's people can only prevent everything around them through unremitting vigilance.