Why do you want to transport vegetables from the far south? Is it because vegetables from other places are more nutritious?

Alien invasive organisms refer to an organism that moves from its place of origin to another geographical area without its place of origin, and establishes a population in it well, and then spreads to affect the surrounding environment, which has a significant impact on the structure and function of the ecosystem in the newly distributed area, causing serious ecological harm and economic losses. It sounds like ecological invasion is still far away from our life, but if you look closely, you will find that the invaders have quietly come to our side.

2. Examples of alien invasion

1. Invasion status of crayfish in China

As a kind of food, crayfish has been loved by more and more people in recent years. Its bright color alone makes people's appetite open, and more importantly, it is fresh and nutritious. Not only in China, but also in many countries in Europe and America, people like to eat crayfish. But he is a real intruder. The scientific name of crayfish (procambius clatkii) originated in South America, and now it is cultivated all over the world, and has formed a large number of wild populations. In China, crayfish was introduced from Japan during World War II. At first, it only bred in Nanjing and its suburbs, and now it has spread to a large area in southern China. At first, it was a process of natural diffusion, because crayfish has strong pressure resistance and can survive in various temporary water bodies. In addition, it can crawl on land, especially in rainy season, a crayfish can crawl for more than ten kilometers. Moreover, the Jiangnan area of China is very suitable for its survival, as well as the surrounding Anhui and other places. Recently, it has been reported that Zhejiang and Dongting Lake are both flooded. Crayfish has a pair of pincer-shaped claws, which looks very dignified and is very suitable for crayfish's burrowing habits. This is a headache for many farmers: these caves will lead to the loss of irrigation water and destroy the fields. Being good at digging holes also makes these small shrimps may endanger the reservoir dam. Nowadays, crayfish have done more harm to reservoir dams than termites and voles. The most important thing is that it will affect the local biodiversity. Today, people all over the world are looking for ways to stop crayfish from expanding wildly, but compared with its amazing breeding speed and fighting against the harsh environment, what we can do is very limited.

When crayfish appeared on our table, other intruders were getting closer and closer to our lives.

2. The distribution of water hyacinth in China.

Eichhornia crassipes, also known as water hyacinth, originated in South America. It was introduced into China as a feed plant for livestock about 190 1 year. It was widely planted as a plant for viewing and purifying water quality, and then spread to tropical and subtropical regions. It is generally regarded as a wild plant in southern and southwestern China. 1944, the water surface of Dianchi Lake near Kunming, Yunnan Province was completely covered by dense water hyacinths. 1999 After winter, Eichhornia crassipes flooded into Huangpu River and Suzhou River in Shanghai, connecting them for more than 30 kilometers, which not only blocked the rivers and affected navigation, but also caused floating garbage such as plastic bags and wrapping paper to flow down the river, seriously affecting the city appearance. (Ding Jianqing et al.,1995; Li Bo et al, 200 1) Water hyacinth has become one of the most invasive malignant aquatic weeds in China. Its rapid spread has caused huge economic losses to fishery production and tourism, but also led to the decline of the diversity of native aquatic plants in China, which has brought serious threats to biodiversity in some areas.

The intruders around us are not just crayfish and water hyacinths. Then, how do these uninvited guests enter the house, and what kind of problems will they bring to mankind? In nature, the spread and migration of organisms is a common phenomenon. Dandelion, which we are familiar with, spreads its seeds by wind. Some plants will use the power of the current to complete the migration, and even use animals, such as Xanthium sibiricum, whose seeds will be attached to the fur of passing animals with natural barbs and taken to other places. Plants and some microorganisms will also follow migratory birds to leave their original places of life. But after all, the spread of this creature itself is very limited, and it is even more impossible to enter a completely different ecological field to settle down and form a population to cause harm and eventually become an intruder.

Three. The influence and promotion of human beings on biological invasion

Humans appeared after the end of the Quaternary Glacier. During the long-distance migration, our ancestors always brought some creatures into new areas intentionally or unintentionally. However, it was not until Columbus discovered the New World and with the conquest of the ocean that human beings were able to set foot in more and more areas, and this biological invasion caused by human factors really became dangerous. Especially in recent hundreds of years, with the process of global integration, those naturally formed natural barriers have gradually lost their due role. With the help of human beings, alien species travel across the ocean, reach new living environment and habitat, and reproduce and spread. During the period of 1820- 1930, more than 50 million Europeans immigrated to distant America and Oceania, and they took away a lot of animals and plants. In this way, mice were taken to many islands without rodents, where the original animals and plants were defenseless against mice. Therefore, the arrival of this greedy creature has led to the extinction of many native species and the massive reduction of some species, and also caused great changes in the ecosystem. After rats appeared, 30 species of 55 tropical Pacific seabirds became extinct, and 7 species of 10 lizards became extinct. Cats, the natural enemy of mice, have also become a nightmare for Australian wildlife. Legend has it that this cat was brought to Australia in a shipwreck in the17th century, but it actually came here with European immigrants in the18th century. At first, they were just ordinary domestic cats, but immigrants released these domestic cats into the wild, hoping that they could control the number of mice and rabbits. These cats have developed sharper vision, smell and hearing than domestic cats in the wild. Their bodies are bigger and their muscles are more developed than domestic cats, which enables them to pounce on their prey at once. Wild cats can adapt to almost all living environments in Australia, even the desert, because they can get the water necessary for life from the blood of their prey. Excellent adaptability makes them one of the most widely distributed and destructive animals in Australian history. Wild cats can also carry and infect people and animals with many infectious diseases, such as highly dangerous toxoplasmosis, which can lead to abortion of pregnant women or birth defects of babies. Nowadays, in order to protect the animals threatened by wild cats, people have built a special fence to stop the silent footsteps of wild cats. However, this kind of fence is expensive and needs frequent maintenance, and a small loophole will also give wild cats an opportunity. In recent years, people have found traces of cats on more distant islands, which once again took advantage of people's negligence and crossed the natural barrier.

In the war, the army will also bring species migration, including many bacteria and viruses that directly endanger human health. For example, measles was brought to America by conquerors from Europe, and syphilis was introduced to Europe from America. Human means of transportation often become the carrier of biological invasion. For a long time, many marine organisms have been attached to ships for migration and diffusion, and the ballast water stored in order to keep the balance of large ships has provided convenience for these aquatic intruders.

Four. Current situation of biological invasion

These creatures have either migrated naturally or, with the help of manpower, reached the environment far away from their original place through different channels. What will be waiting for them here, and what will they bring to mankind?

Many of our foods are not native species. Why didn't these fruits and vegetables become terrible invaders? In fact, only a small number of alien species can really invade, but it is this small number of alien invaders that have caused great losses. There are no rabbits in Australia. 1859, Thomas was British.