The sixth lesson, Biological Invaders

, is selected from the first volume of Chinese, the eighth grade experimental textbook of compulsory education curriculum standard.

you won't be surprised when you find one or two beetles you've never seen before on the roadside grass or in your yard. But in the eyes of biologists and ecologists, this may not be a trivial matter. Experts call this kind of "immigrants" who originally lived in a foreign country and went to a new ecological environment through unnatural means "biological invaders"-they will not only destroy the original ecological system in a certain area, but also cause incalculable economic losses to human society.

In the early days of human civilization, land and navigation technologies were underdeveloped, and the ecological balance in nature was not greatly damaged. Under natural conditions, a dandelion seed may drift with the wind for thousands of meters before landing. If all conditions are suitable, it will take root, sprout and grow there. Fish and shrimp in mountain streams may swim with the water to settle down in big rivers ... All these things are carried out slowly without human intervention, and the time and space span are very limited, so it will not cause serious imbalance of the ecosystem.

If a species is not restricted by many factors, such as food competition of the same species and harm from natural enemies, in the new living environment, it is likely to breed uncontrollably. In 1988, several mussels (mollusks similar to mussels) originally living in the European continent were brought to the North American continent by a cargo. At that time, these "stowaways" mixed in the cargo at the bottom of the warehouse did not attract the attention of the local people, and they were casually discarded in the waters near the Great Lakes. Unexpectedly, however, it has become a "paradise" for bamboos. Without the restriction of natural enemies, the number of scallops has increased dramatically, and almost all the hydrophobic pipelines in the Great Lakes have been "occupied" by them. So far, people have spent billions of dollars to clean and replace pipelines. Anoplophora longicorn from Asia and red ants from South America are two other "invaders" that plague Americans. The former madly destroys trees in Chicago and new york, while the latter specializes in biting people and animals and spreading diseases.

"Biological invaders" not only cause incalculable economic losses to human beings, but also pose a great threat to other species and species diversity in the invaded areas. During World War II, the palm tree snake settled in Guam with a military cargo ship. This reptile that lives in trees specializes in preying on birds, attacking bird nests and swallowing bird eggs. Since World War II, nine of the 11 native birds in Guam have been wiped out by palm snakes, and the number of the two remaining birds is decreasing day by day, which is in danger of extinction at any time. Some biologists have seen palm snakes six times on the plane from Guam to Hawaii. They warned that there are no natural enemies on the island of Hawaii that can curb the reproduction of palm tree snakes. Once the palm tree snakes settle down in Hawaii, the birds on the island will be doomed. Many biologists and ecologists blame the increase of "bio-invaders" on the increasingly prosperous international trade. In fact, many "bio-invaders" take the "hitchhiking" of transnational trade to achieve the purpose of "smuggling". Take the current global fresh fruit and vegetable trade as an example, many insects and insect eggs are attached to these goods, including extremely harmful pests, such as Mediterranean fruit flies. Although the animal and plant quarantine centers of customs in various countries strictly guard against these pests, it is difficult to ensure that there are no "bugs" that escape the net because of the huge amount of imported and exported goods. In addition, transnational pet trade also provides convenience for "biological invaders". In recent years, the news that the introduction of colorful ornamental fish has brought cholera to some areas is often seen in newspapers. Some pets from other places, such as snakes, lizards, bobcats, etc., often escape because of the negligence or abandonment of their owners, harming one party.

Some biologists point out that once a certain "biological invader" gains a foothold in a new environment and breeds on a large scale, its number will be difficult to control. Even in today's highly developed science and technology, people will still be helpless in the face of those animals and plants with strong adaptability and reproductive ability.

Some scholars in biology and ecology argue that human beings should not interfere too much in the migration process of biological species, because the imbalance is temporary, and a species must follow the law of natural selection in the new environment. Not all "biological invaders" can survive, but the strong ones can survive. Even the strong ones in the ecosystem are also restricted by various factors in the system and cannot do whatever they want. Therefore, the balance of nature will eventually be realized. However, more scholars are against it. They think that the process of natural regulation is very long. If "biological invaders" are allowed to develop freely, many native species will be doomed to extinction, and the species diversity in nature will be seriously damaged. In addition, the economic losses caused by "biological invaders" to human society are amazing. In the United States alone, the annual economic losses caused by "biological invaders" are as high as more than 2 billion dollars. How can people be indifferent to such astronomical figures?

At present, many countries in the world have begun to realize the seriousness of this problem and taken corresponding measures. For example, in 1996, the U.S. House of Representatives passed a bill requiring relevant agencies to strengthen the monitoring of vehicles that may carry alien species. For this reason, the U.S. government is planning an inter-departmental monitoring plan.

In the mid-19th century, a European explorer came to the Mexican jungle and saw this plant called "Mykonia" for the first time. It belongs to the family Paeoniaceae, usually more than ten meters high, without flowers, but it has wide and thick leaves-the sunny side is green, while the shady side is bright purple, which is very special and beautiful. Explorers were attracted by "Mykonia", picked its leaves and fruits, and brought "Mykonia" back to the European continent together with other exotic foreign objects.

In p>1961, a European gave a bag of seeds of "Mykonia" as a gift to a botanical garden in Hawaii. "Mykonia" has strong growth and rapid reproduction. Before long, "Mykonia" was sold to the nursery and became a very popular ornamental plant on the island of Hawaii.

But at that time, no one found that "Mykonia" is a destructive plant, and its arrival will bring great changes to this land.

experts point out that although the growth of plants seems calm and uncontested, in fact, the world of plants, like the animal kingdom, is full of struggles between you and me. Plants with strong viability often plunder and destroy the living resources of other plants.

McConia is one of them. Another alien creature, the dark green embroidered bird from Japan, inadvertently became an "accomplice" of McConia. Dark-green embroidered birds like to eat the fruit of Mykonia very much, although the fruit of this plant is very small, and there are hundreds of seeds in each fruit. After eating the fruit, the dark green embroidered birds become voluntary seeders. They fly freely in the jungle and spread undigested seeds in all directions.

Because there are no natural enemies in Macania, Hawaii, it has suitable temperature, fertile soil, abundant sunshine and water, so each plant can fully stretch around at will, absorb water and take up space. In just over 4 years, the coverage area of "Mykonia" on the big island of Hawaii has reached 1, acres, about 4, hectares. The tall and straight "Mykonia" plant is like handfuls of green umbrellas. In its shadow, the relatively small native plants in Hawaii gradually wither and die because they can't get enough sunshine, water and nutrients. It was these native plants that were originally used by the local people to conserve the precious fresh water on the island of Hawaii and feed a variety of animals that ate them. What is even more frightening is that the decline of the survival of dwarf plants has also led to the increasing loosening of forest soil and the danger of mudslides at any time. Faced with such tenacious vitality and irresistible destructive power, biologists compare it to "green cancer".