biological invasion

Some "biological immigrants" (perhaps a kind of bacteria, a plant or an animal) who traveled across the sea came to a foreign country, gained a broad living space because of losing the balance of natural enemies, and grew rapidly, occupying lakes and land, while "indigenous creatures" withered or even died out. This is a biological invasion.

People may not be familiar with biological invasion, but when it comes to foot-and-mouth disease, mad cow disease and even AIDS, people are no strangers. In fact, these are all kinds of biological invasions. Some animals and plants often mentioned in the past are also invasive creatures in some places, such as morning glory, water hyacinth, Mediterranean liriomyza sativae, lantana and whitebait.

The strengthening of free trade, economic globalization and the substantial growth of trade and tourism provide more opportunities for the accidental or intentional spread of species than before. Airplanes, ocean-going ships, and a traveler trekking between continents may "land" in a strange environment with species. "Every ship, every plane and every truck is a potential carrier," said an expert.

Irrefutable evidence.

A booklet published by the International Union for Conservation of Nature and Natural Resources identified 100 species as the most aggressive species in the world. Some of them have caused disastrous consequences to the local ecological environment.

(1) A zebra mussel from Asia spread wildly in the United States, resulting in a sharp decline in the number of local mussels and some fish. The affected areas include the Mississippi, Tennessee, Cumberland, Ohio, Arkansas and Illinois rivers.

(2) Lake Victoria was covered by an exotic aquatic hyacinthus orientalis, resulting in the death of a large number of local plants. As a result, most of the lake is navigable. Although two years ago, the authorities deployed a lot of manpower and material resources to eradicate this plant. But soon hyacinthus orientalis made a comeback and occupied more than half of the lake again.

(3) In the early 1970s, a kind of perch (a large freshwater carnivorous fish) native to the Nile River proliferated in Lake Victoria, and the native fish in the lake were almost extinct.

(4) In the early 1980s, a crown jellyfish was brought into the Black Sea by marine workers. At present, this jellyfish accounts for 95% of the biomass in some areas of the Black Sea. It feeds on zooplankton, eggs and some fish, resulting in a sharp decline in the number of anchovies in the local waters, and the local fishery with an annual output of 250 million US dollars almost collapsed.

(5)1In the early 1950s, Guam introduced a palm snake. Since then, 12 species of birds have disappeared from the island, and some other species are close to extinction. The number of snakes per square mile in some forest areas of Guam is as high as 13000. Since 1978, there have been more than 1200 power outages caused by snakes crawling on power lines. These snakes have also destroyed a lot of power equipment and become an important economic burden for Guam.

(6) In the past two years, Florida was invaded by two species, but it didn't cause much damage. In 2000, a gentle snakehead was found in the southern waters of Florida, where it has been developing slowly. But this snakehead can't live in the water below 10 degrees Celsius. An Asian eel was also found in the waterway of Florida, which may have spread to the swamp area.

(7) A giant pink jellyfish native to the Caribbean Sea spread to the Gulf of Mexico and constantly preyed on the local common jellyfish. This pink jellyfish can reach 3 feet in diameter, and their tentacles can reach 70 feet (2 1 m). Pink jellyfish was first discovered in September 2000, spreading from the west coast of Florida to the west of Louisiana. Scientists estimate that the number of pink jellyfish in some areas of the Gulf of Mexico has reached thousands per square mile.

(B) the introduction path of alien species invasion

There are three main ways to introduce alien species: unintentional introduction, intentional introduction and natural invasion.

Some creatures were introduced unintentionally. For example, in order to engage in image projects, some areas do not introduce big trees from abroad through customs. The introduced trees look good, but there are no pests, larvae and eggs in the trunk, leaves and soil. A typical example is Eupatorium adenophorum, a malignant weed. Where it grows, other plants cannot grow. It occupies nutrition and space, and grows so fast that the creatures growing under it can't get sunlight. In some areas of Yunnan, China, pine trees are above and Eupatorium adenophorum is below.

There are also some creatures that are intentionally introduced and unscientific. Such as water hyacinth, because it is a very beautiful ornamental plant and contains a small amount of starch. China introduced it for ornamental purposes and as feed. However, its growth rate is very fast after its introduction. Last year, in Dianchi Lake, Yunnan Province, the water there became like green paint. The main reason is that the water hyacinth grows wildly and then rots, and the pollution is very serious. It is unscientific to introduce it without full argumentation. Just like there are no rabbits in Australia, after more than a dozen rabbits were introduced from Britain, they have become a scourge because they have no natural enemies, so it is necessary to be cautious to introduce exotic creatures. About half of the invasive species migrate by accident. For example, when you come back from an overseas holiday, your dirty shoes will bring back some bugs. However, sometimes species invasion is not accidental. A boy from Hawaii brought some snails to his grandmother in Miami. He thought his grandmother would like them, but unfortunately, she didn't like them and threw them away A year and a half later, scientists discovered this snail, but by that time they had pushed some local species to the brink of extinction. It took people seven years and a lot of money to finally destroy them.

Humans have migrated species for thousands of years. When people move to a new place, they also bring animals and plants there. At that time, because travel was still slow, it was easier to control their harm. But now, many people travel long distances every day, which leads to the widespread spread of many harmful species. Sin Beloff said, "Australia and New Zealand have done a lot to slow down the spread of species. They check their luggage at the airport to confirm whether there are any overseas species. On the other hand, the inspection measures of the United States and other countries are not very strong. "

Many simple and easy methods can help people solve this problem. Wash your shoes and clothes and get rid of bugs before you come back from overseas. Before the summer camp is over, pat your bag and let the insects in the forest stay in their Woods. Scientists also advise people not to take animals and plants with them when traveling. Passengers sometimes hide exotic creatures such as lizards, parrots and bugs in their luggage and take them home as pets or gifts. Their original intention was good, but the result was disastrous.

(3) The harm of biological invasion is mainly manifested in three aspects: destroying the ecological environment, threatening human health and endangering economic development.

First of all, alien invasive species will cause serious ecological damage and biological pollution. Most exotic species broke out after successful invasion, and their growth was difficult to control, resulting in serious biological pollution and irreversible damage to the ecosystem. For example, water hyacinth, which originated in South America, has now spread all over rivers, lakes and ponds in North China, East China, Central China and South China. In Dianchi Lake, with a continuous area of 1 1,000 hectares, water hyacinth grows wildly, covering the water surface, seriously destroying the structure and function of aquatic ecosystem, resulting in the death of a large number of aquatic animals and plants. Alien invasive species form a single dominant population by suppressing or crowding out local species, which endangers the survival of local species and eventually leads to the loss of biodiversity. For example, Eupatorium adenophorum, which originated in America, has spread all over most parts of southwest China, and always appears in the form of a single superior plant community in its place of occurrence, which has led to the decline and disappearance of the original plant community.

Secondly, it threatens human health. Alien invasive species not only bring great losses to the ecological environment and national economy, but also directly threaten human health. Ambrosia and Ambrosia trifoliata are now distributed in Northeast China, North China, East China and Central China 15 provinces and cities. The pollen produced by ragweed is the main pathogen causing human pollen allergy, which can cause hay fever. Apart from mad cow disease and foot-and-mouth disease, the disasters brought to human beings are very painful, because harmful organisms are endangering human health and the safety of agricultural organisms all the time. In the second half of the fifth century, the plague invaded the Middle East from Africa and then reached Europe, killing about 654.38 billion people. 1933 China classical swine fever epidemic, resulting in the death of 9.2 million pigs. 197 avian influenza occurred in Hong Kong, and 6,543,800+4,000 chickens had to be destroyed. Only the losses of chicken farmers and chicken vendors were compensated, totaling HK$ 654.38+0.4 billion.

In addition, biological invasion leads to frequent outbreaks of ecological disasters, causing serious damage to agriculture and forestry and endangering economic development. In recent years, the serious occurrence and damage area of forest invasive pests such as Bursaphelenchus xylophilus, Pinus elliottii, Hemiberlesia pitysophila and Hyphantria cunea have increased year by year. Ragweed, Eupatorium adenophorum, Eupatorium odoratum, Mikania micrantha, Alternanthera philoxeroides, Eichhornia crassipes, Spartina, etc. It has spread wildly and has reached an uncontrollable level. According to experts' estimation, the annual losses caused by biological disasters in China account for 10%- 15% of grain output, 15%-20% of cotton output and 20%-30% of fruit and vegetable output.

(D) the reasons for the alien invasion

At present, the reasons for the foreign invasion in academic circles are not clear, which can be discussed from two aspects. One is from the perspective of intruders, and the other is from the perspective of invaded ecosystems. Biological invasion goes through several stages: transmission, settlement, growth and reproduction. Alien species are brought to places where they have never lived before through people's activities, intentionally or unintentionally. Some of them successfully took root and began to grow, while others ended up "he died before he conquered" because of "acclimatization" and other reasons. The species that established the base gradually adapted to the local environment, and slowly began to use their own advantages to continuously expand the occupied area, effectively use resources, and expel local species.

Generally speaking, invasive species have some corresponding characteristics. For example, plants can produce a large number of seeds, while animals produce a large number of eggs or offspring, which not only increases the absolute number of offspring, but also increases the probability of their spread, which has advantages in the first stage of invasion. In order to explain these phenomena, scientists put forward the following hypotheses: niche vacancy hypothesis, biological factors out of control hypothesis, community species richness holiday theory, and interference hypothesis before and after migration.

Niche vacancy hypothesis means that in a stable ecosystem, there is already a species in each position, just like the saying "a radish is a pit", so that the foreign radish has nowhere to go and the invasion will not happen. If there is a "radish" missing somewhere, and it happens that the foreign radish is just suitable for this pit, then the invasion will happen.

The central idea of the hypothesis that biological factors are out of control is that the survival and reproduction of alien invasive species in new areas are not caused by the characteristics of invasive species themselves, but by their accidental arrival in a new environment without natural enemies or other biological restrictions, so their rapid spread has caused disasters. That is to say, alien creatures are harmless in the country of origin because the country of origin has natural enemies or other biological factors that limit their catastrophic outbreak, and these annoying nemesis just disappeared in the invaded place, so these outsiders lose no time to do whatever they want. This hypothesis is the most direct hypothesis to explain the successful invasion of alien species, which urges people to find their natural enemies in the origin of invasive species for biological control.

In addition, there is another important phenomenon of alien invasion, which is "time lag". It refers to the time delay period (incubation period) between the alien invasive organisms begin to settle in a new environment and the rapid growth of population and the rapid expansion of occupied area. That is to say, invaders will not multiply and expand their territory in the initial time, but will grow quietly in the newly arrived places. For example, Brazilian pepper was introduced to Florida in the19th century, but it was not known until the early 1960s. Now, in Florida, they have occupied an area of 280 thousand acres, and the community is dense, and no other plants can compete with them.

There is also a plant called Senecio scandens, which grew only in Oxford Botanical Garden at the end of18th century, but soon spread to many places in Britain in the middle of19th century. The time lag in the process of alien invasion, with or without it, is short or long, from just a few years to decades or hundreds of years, or even more, which can last for centuries. This makes the invasion of alien creatures even more elusive. Maybe some alien creatures around us that have not been known for a long time will suddenly explode and bring a lot of trouble to mankind.

As for the reason of "time lag", it is still unclear. The possible reasons are as follows: (1) Because the original habitat of alien species is not suitable for their survival, it takes time to spread to the environment suitable for their growth; (2) due to natural barriers such as roads, rivers and valleys or human restrictions, it cannot spread to other areas conducive to growth; (3) Because the population is too small to attract people's attention, the population has been growing. This is related to people's understanding and concern about alien species; ④ The number and distribution of potential intruders. If a population wants to breed quickly, it needs to reach a certain population size, and the invaders will not break out on a large scale before breaking through this critical point; ⑤ The time required to produce the genetic variation of the new genotype adapted to the new environment; ⑥ Waiting for the change of habitat. Some alien species can maintain their own survival under unfavorable living conditions, but they cannot erupt. Once the growth conditions are suitable, it will expand rapidly and wait for an opportunity to explode.

(5) Classic cases

1. Enlightenment from Australian Rabbit

Historically, the introduction of alien species into a certain region and its serious consequences became known with the history of European colonial expansion. From AD 1500, with the process of European overseas expansion, Europeans brought pigs, cattle, sheep, horses and other livestock to America and Oceania. When these animals escape and become wild, they spread rapidly in various habitats. It is undeniable that such species migration has played a positive role in human survival and development. However, history tells us that if the introduction of non-native species is not effectively guided and controlled, it will seriously endanger the production, life and ecological environment of local people. 1859, an Australian farmer brought some rabbits from abroad to hunt, and a terrible ecological disaster broke out. Rabbits are famous rapid breeders. In Australia, it has no natural enemies. As its population doubled, it soon began to destroy crops. At 1880, they arrived in New South Wales and began to influence the sheep industry in South Australia. People organized a large-scale rabbit killing operation, but it had little effect. In the 1990s of 19, when the rabbit arrived in Western Australia, people built a fence 1000 miles long to try to stop it. However, the fence was soon broken down. From 65438 to 0950, the number of rabbits in Australia increased from the initial 5 to 500 million, and crops or grasslands in most parts of the country suffered huge losses, and some small islands even experienced soil erosion. In desperation, myxomatosis was introduced from Brazil to deal with the rapidly multiplying rabbits. However, the germ warfare against rabbits proved to only temporarily alleviate the deteriorating situation. A few rabbits have natural immunity to this virus and reproduce quickly after escaping. Throughout the mid-20th century, rabbit killing activities in Australia never stopped.

2. Plant migration is accompanied by pests and diseases, and exotic plants will also have an impact on local species.

In California, there were only three exotic plants in 1769, but a century later, there were 9 1 species of exotic plants, and European plants accounted for half of the local vegetation. Rosa roxburghii was introduced to Australia on 1839 to provide hedges. It soon bloomed in Queensland and New South Wales, forming an obstacle more than six feet high. By 1925, 60 million mu of land will be affected, and half of these areas cannot grow any plants except Rosa roxburghii. Finally, by introducing South American caterpillars that feed on Rosa roxburghii, Rosa roxburghii will be controlled in a certain area.

3. China's "Wolf is coming"

Recently, a tropical fish in Nanning ornamental fish market has become the target of the relevant departments in Guangxi. This beautiful and colorful tropical fish is called "piranha", and piranha is also called "wolf clan in the water", which is what we commonly call "piranha". Man-eating pomfret is native to the Amazon River basin in South America. It is violent and aggressive. Even in its native South America, it is considered a very dangerous creature. According to related reports, more than 1000 buffaloes are eaten by piranhas every year in the Amazon river basin, and piranhas attack humans from time to time. For Guangxi, the more realistic threat is that once these tropical small fish introduced as ornamental fish enter rivers and lakes, other local aquatic organisms will face extinction. The natural environment in Guangxi is similar to that in South America, and piranhas have no natural enemies. After entering Guangxi, it will form dominant species and destroy the ecological balance.