On the Invasion of Alien Species

1. Invasion status of alien species in China

China is one of the countries with particularly rich species diversity in the world. There are 2,554 species of terrestrial vertebrates, 3,862 species of fish and about 30,000 species of higher plants, among which invertebrates include insects, lower plants, fungi, bacteria and actinomycetes. According to literature records and preliminary investigation, there are more than 600 species of exotic naturalized plants in China, including exotic weeds 108, belonging to 23 families and 76 genera, and 15 species are considered as national or regional. At present, there are about 40 species of exotic animals that seriously harm our country, including Hyphantria cunea, Hemiberlesia pitysophila, Pinus elliottii, Rice Water Elephant, Liriomyza sativae, Bursaphelenchus xylophilus, sugarcane borer, Sitophilus graminis, Tetranychus urticae, potato beetle, Dendroctonus valens and so on. Other exotic animals, as well as the big bottle snail originated in South America, the brown cloud agate snail originated in East Africa, the muskrat originated in North America, the squirrel originated in the former Soviet Union and the nutria originated in South America. The introduction of exotic fish also poses a great threat to local fish species and lake ecosystem. The biggest threat to biodiversity in Yunnan waters comes from invasive fish, such as grass carp, silver carp, bighead carp, new whitebait in Taihu Lake, wheat-ear fish, goby fish and goby fish in Bokou. At present, foreign microorganisms or diseases that are harmful to agriculture, such as bacterial leaf streak of rice, endophytic syncytium, Phytophthora sojae, Verticillium white rot, citrus Huanglongbing, citrus canker (Xanthomonas citri) and cassava bacterial wilt (Xanthomonas campestris PV. Manihotis), tobacco ringspot virus disease, tomato canker disease (Corynebacterium michigan subspecies. Mishiganen), scale bulb nematode (Ditylenchus spp.), and so on.

However, among the vast biological species in China, it is still unknown how many exotic species there are. At the same time, China is vulnerable to alien species. Because China is 5,500 kilometers long from north to south and 5,200 kilometers wide from east to west, spanning 50 latitudes and 5 climatic zones (cold temperate zone, temperate zone, warm temperate zone, subtropical zone and tropical zone), most exotic species from all over the world may find suitable habitats in China.

Invasion of alien species in China has the following characteristics:

A. Coverage: Invasive species have been found in 34 provinces, municipalities and autonomous regions. By May, 2002, China * * had established 65,438+0,500 nature reserves, accounting for about 9% of the country's total area. Except for a few remote nature reserves, invasive species can be found more or less.

B there are many ecosystems involved: almost all ecosystems can be seen from forests, agricultural areas, waters, wetlands, grasslands and urban residential areas. Among them, the ecosystems in low-altitude areas and tropical islands are the most seriously damaged.

C there are many species involved: examples can be found in vertebrates (mammals, birds, amphibians and reptiles, fish), invertebrates (insects, crustaceans, mollusks), plants, bacteria and viruses.

D. Serious harm: Many places in China have stopped cutting down virgin forests, and it is strictly forbidden to further destroy the ecology. Alien invasive species have become an important cause of ecological degradation and biodiversity loss, especially for aquatic ecosystems in the south and tropical and subtropical regions, and have become the first important influencing factor.

2. The main ways (channels) of alien species invasion

The most fundamental reason of biological invasion is that human activities have brought these species to places where they should not appear. So we call these species "harmful", which is actually unfair to these species. They just stay in the wrong place, and the cause of this mistake is often some irresponsible activities of human beings. The key to the problem of alien invasive species is man-made. Introduction means that species, subspecies or taxonomic units below subspecies (including all parts, gametes or propagules that may survive and then reproduce) are transferred by humans to areas beyond their (past or present) natural distribution range and diffusion potential. This transfer can be carried out within countries or between countries. Introduction can be divided into intentional introduction and unintentional introduction.

Intentional introduction refers to the purposeful introduction by human beings, which moves a species out of its natural distribution range and diffusion potential (this introduction can be authorized or unauthorized).

Unintentional introduction refers to the unintentional introduction of a species through human or human communication system and its spread to places outside its natural distribution.

Exotic species are introduced into their non-native areas in these two ways.

Intentional introduction

China has a long history of introducing excellent varieties from other places or abroad. Early introduction was usually achieved through ethnic migration and regional trade. The seeds of sour bean (sour horn), grape (grape), alfalfa, pomegranate (pomegranate) and safflower (safflower) originated in Africa passed through the ancient famous "Shu-Toxoplasma gondii (India) Road" in the 4th century BC and 1 century BC respectively. Since then, in the Northern Song Dynasty, Aloe vera (or Aloe vera). Chinensis) (originated in northeast Africa and now naturalized in the coastal areas of South China),17th century, economic plants such as sweet potato, tobacco and passion fruit were introduced into China. Earlier, the Dutch introduced some American species, such as Leucaena, Acacia and pitaya, to Taiwan Province Province, and most of these species were later naturalized as wild plants. 1842 After the Opium War, Hongkong, Guangzhou, Xiamen, Shanghai, Qingdao, Yantai and Dalian became the main entrances for exotic weeds to enter China. Weeds such as Erigeron canadensis (1857), Erigeron canadensis (1862) and Erigeron annua (1886) landed in Hong Kong, Yantai and Shanghai successively, and gradually spread to the mainland. The introduction time and escape place of some cultivated plants are irregular. For example, French missionaries introduced Vitex negundo into the vicinity of Chengkou Church in Sichuan, and then a large number of Vitex negundo escaped.

At present, almost all planting and breeding units are imported from other places or abroad. These departments or units include agriculture, forestry, gardens, aquatic products, animal husbandry, special aquatic products and various breeding bases. Most of them were introduced to improve economic benefits, ornamental and environmental protection, but some species became harmful because of improper introduction. Among the known exotic harmful plants in China, more than 50% species are the result of artificial introduction.

The purpose of intentional introduction is varied, which can be mainly divided into the following aspects:

As pasture or feed

There are many examples of invasion caused by the introduction of pasture or feed. For example, Alternanthera philoxeroides, alfalfa, clover, sunflower, millet, white grass, Pennisetum, Sudan grass, ryegrass, water hyacinth, barley, water hyacinth and so on. Long-term overgrazing and grassland degradation in China's animal husbandry have increased the demand for new high-quality fast-growing grasses, which provides an excellent opportunity for foreign grass seed companies to dump grass seeds in China. At present, a large number of new forage experiments are being carried out, mostly to test whether the varieties provided by foreign grass seed companies can grow rapidly on our land. Worryingly, some of them have become dangerous alien invasive species. Alternanthera philoxeroides, commonly known as "Alternanthera philoxeroides", was introduced and spread in many places in southern China as pig feed after 1950s, and later became wild. 1986 investigation shows that Alternanthera philoxeroides has a natural occurrence area of about 889 600 hm2 and has become the main weed in vegetable, sweet potato and other crop fields and citrus orchards.

As an ornamental plant

The pursuit of exotic flowers urges people to introduce exotic or foreign varieties of flowers. These flowers and plants inevitably escape from the garden. Under natural growth, some exotic ornamental plants escape and become dangerous alien invasive species. Such as Pogostemon Pogostemonis, Coreopsis verticillata, cosmos, Heliqiu, Tagetes erecta, Solidago canadensis, Petunia hybrida, Petunia rotundifolia, Lantana, Mimosa, Oxalis pubescens, Allium tuberosum, Vitex negundo, and Chlorophytum.

The popularity of aquariums and family aquariums also makes some exotic aquatic plants become invasive species. For example, Cabomba Carolina, which originated in the United States, has now appeared in rivers in Zhejiang; Aquatic Myriophyllum from South America has been introduced in Taiwan Province Province. Although the former only blooms but does not bear fruit, the latter only has female plants, and neither of them produces seeds, but they can spread rapidly through asexual reproduction. For example, the green algae (Caulerpa taxifolia) introduced into the French aquarium from the Adriatic Sea formed a dominant population in the French local marine ecosystem by releasing spores, which led to the mass extinction of local marine plants. Lantana is native to tropical America. During the period of 1645, it was introduced to Taiwan Province Province by the Dutch as an ornamental plant. Now it is spreading in tropical and subtropical areas of China, crowding out local plants and blocking roads. Its plants have an unpleasant smell and its stems have thorns, so it is a harmful shrub. Its fleshy fruit is further spread by local birds pecking. Scavengers often kept in aquariums are a species of the genus Spotted Fish, which is native to Latin America. Recently, it has been reported that it has been collected in the Nanchanghe River in Beijing, the Pearl River and the Hanjiang River in the south. It is reported in Dongshan River, Yilan County, Taiwan that this species has no natural enemies in Yilan, but it is very fertile, laying 300-500 eggs at a time, and the hatching rate is almost 100%. Feeding on the eggs of other fish gradually reduced the native species in Taiwan Province Province. To this end, Yilan also launched a fish cleaning operation.

As a medicinal plant

12000 Many kinds of organisms used in Chinese medicine are mostly native to China, some are exotic species, and some have become invasive species. Such as soap grass, cassia obtusifolia, cassia obtusifolia, evergreen, wangjiangnan, Phytolacca acinosa, Datura stramonium, ice eggplant and so on.

As a plant for improve that environment

In order to quickly solve the problems of ecological environment degradation, vegetation destruction, soil erosion, water pollution and so on, people often look at some characteristics of alien species unilaterally, which provides an excellent opportunity for the invasion of alien species. At present, many areas are actively carrying out vegetation restoration, but some of the species used are dangerous alien species. At present, some species have invaded, such as Spartina alterniflora, Mikania micrantha and Eichhornia crassipes. Spartina alterniflora was introduced from the salt marsh vegetation on the east coast of the United States in 1979. First, 1980 and 10 were planted in Fujian coastal areas, and then widely publicized. 1982 expanded to Jiangsu, Guangdong, Zhejiang and Shandong. The purpose of introduction is to protect beaches and revetments, improve soil, green beaches and improve the ecological environment of beaches. Now this species has fled from Zhejiang, Fujian, Guangdong and Hong Kong. 1990, the annual loss of aquaculture in Dongwuyang, Ningde, Fujian alone reached more than 10 million yuan. This species has become a serious problem in coastal areas, affecting the local fishery output and threatening mangroves.

Exotic species are also widely used in urban landscape construction and beautification, which often causes complete changes in local ecosystems and landscapes. Taking lawn industry as an example, with the large-scale construction of lawns with different functions (golf courses, football fields, parks and green spaces, etc.), it has promoted the rapid development of lawn industry in China, and the demand for lawn grass seeds has increased sharply. At present, the grass species used are mainly excellent lawn varieties from abroad. Except Zoysia japonica seeds, almost all other grass species are imported, and the import volume of 1997 alone reaches more than 2,000 tons. Up to 1990, China has introduced 1 14 different cool-season grasses, mainly from the United States. At present, some species have invaded, such as carpet grass. In fact, China has a vast territory and rich germplasm resources, and has great potential in grass seed selection.

As food

Food is a part of China's traditional culture, and its emphasis on food diversity is unmatched by any other ethnic group in the world. In order to pursue the color, fragrance, taste, novelty and novelty of food, people introduce a large number of edible animals and plants, but they don't know that this will also cause biological invasion, such as sweet apricots, amaranth and sunflower introduced as vegetables; Guava, Passiflora edulis, and Physalis alkekengi, which are introduced as fruits, are used as raw materials for the production of bean jelly, as well as edible animals such as Pomacea canaliculata and Pomacea canaliculata. The skin of some mammals has high economic value, such as muskrat and nutria. People widely promote farming to obtain animal skins, and as a result, biological invasion has also formed. Pomacea canaliculata was introduced to Guangdong by a Brazilian Chinese in 198 1 for the purpose of being used as cultured food. Since 1984, pomacea canaliculata has been widely cultivated in Guangdong, Fujian, Yunnan and other places. It was released into the wild because of excessive reproduction and bad taste. Pomacea canaliculata has strong adaptability and reproductive ability, large appetite and many kinds of food. It spreads rapidly, destroying vegetables and aquatic crops. Since 1988, Ampullaria canaliculata has caused huge losses in 25 000 hm2 of land in 37 counties of Guangdong Province.

As a cannabis crop

Some hemp crops introduced in ancient times, such as abutilon and hemp, were gradually eliminated and became weeds in many places with the introduction of cotton.

As a pet

Some animals are widely farmed in cities as pets, and some parrots with strong viability, such as Cacacatua sulpurea and Trichoglossus haematotus, have greatly increased their numbers after being wild in the local area, and they have overused strong shrubs or eaten young leaves, endangering local vegetation. Trachemys scripta is a global invasive species, which can be found in almost all pet markets in China from north to south. Although the harm of the Brazilian tortoise has not been reported in China, it has been listed as one of the most dangerous 100 invasive species in the world by the World Conservation Union (IUCN, 200 1), and the Brazilian tortoise is also the vector of disease transmission. The introduction of "pet rats" from South America in Taiwan Province Province has also aroused the fear of disease spread.

As an aquaculture species

Aquaculture is one of the important industries with a long history in China. Almost all the waters that can be used for aquaculture, such as rivers, lakes, ponds, reservoirs, rice fields, parks, etc., are engaged in aquaculture to some extent. The exotic species involved include those introduced from abroad, such as Procambarus clarkii, Macrobrachium rosenbergii, red crayfish, rainbow trout and non-crucian carp (tilapia). ), European eel (Anguilla japonica), white sturgeon (Polyodoh spathula), freshwater pomfret (freshwater pomfret), spotted catfish (Morone saxatilis) and some carnivorous fish (especially small fish), such as California perch (California perch) and striped catfish. Perch introduced from the Irtysh River led to the extinction of Xinjiang bighead carp in Bosten Lake, Xinjiang. In addition to these imported species, China native fish such as "four big fish" (silver carp and bighead carp) were introduced into high-altitude waters in northwest and southwest, and the disasters caused by these species and small miscellaneous fish (tiger fish, wheat ear fish, etc.). ) With the introduction of these species, the impact is no less than that of exotic species. The breeding of bighead carp in Qilu Lake and Xingyun Lake in Yunnan Province has led to a sharp decline in the number of local species of bighead carp in Qilu Lake and Xingyun Lake, and now it has to rely on artificial breeding. For example, Procambarus clarkii was introduced to China from Japan for artificial propagation in the early 1940s. Unlike most aquatic species, female Procambarus clarkii hatches her eggs by herself, so she doesn't need to spend money on artificial incubation. Once put into the pond, Procambarus clarkii can maintain itself without being put into the pond after harvest. Procambarus clarkii is often mixed with other crops, especially rice Those who escaped during the harvest season dug holes in the dam to survive. In the next season, a breeding population will be formed, living on surplus crops and other foods. It was first cultivated in Nanjing, Chuxian and other places in Anhui Province, and then spread to the central, northern and southern parts of China, and became a large population in the wild.

Release in different places

In China, Viet Nam, Malaysia, Thailand, South Korea and Cambodia, people will be respected for releasing captured animals, especially birds, fish and turtles, but a study shows that 6% of the released birds are foreign; Most fish, turtles and soft-shelled turtles are kept in captivity abroad, and these species may be invasive [10]. Obviously, the cultural meaning of "doing good" does not take into account the harmful effects on the local ecosystem. The reason is that people don't have the concept of alien invasive species and don't understand the harm caused by alien invasive species.

There is a bad habit of eating wild animals in southern China. Wild animals are also used as pets and Chinese medicine ingredients. As a result, illegal wildlife trade is rampant. A large number of wild animals come from neighboring countries, especially Southeast Asian countries, and some wild animals are smuggled to China from distant Europe, Africa and America. Our government's trade management of illegal wild animals is also strengthening. But how to deal with the confiscated wild animals often becomes a worrying and headache problem. Because many smuggled wild animals are exotic species, or often carry exotic wildlife diseases. Releasing these confiscated wild animals at will may lead to the death of some species, while others are in danger of biological invasion, posing a serious threat to local wild animals or ecosystems in China. These results run counter to the publisher's original intention.

Introduction of Botanical Gardens, Zoos and Wildlife Parks

Many cities in our country have zoos, botanical gardens and bird gardens. Many exotic plants escaped from the botanical garden, naturalized and invaded. Although there are no reports of invasions in zoos, some species naturally reproduce in the wild. For example, starlings have formed a natural population in Beijing. In particular, it has become fashionable to establish wildlife parks in various places, and a large number of species are scattered in natural areas. If management measures are not strengthened to prevent exotic species from escaping from zoos, botanical gardens, bird gardens and wildlife parks (which may carry exotic wildlife diseases), these potential alien invasive species sources may bring disastrous ecological invasion.

Unintentional introduction

Many alien invasive organisms were inadvertently introduced with human activities. Usually, people and their products are introduced to a new environment as stowaways or "hitchhikers" by planes, ships, trains, cars and other means of transportation. Especially in recent years, with the continuous increase of international trade, the continuous expansion of foreign exchanges and the rapid warming of international tourism, more and more alien invasive organisms have been introduced into China through these channels. In addition to transportation, construction and development, military transshipment, express delivery service, letter mailing, etc. Will inadvertently introduce alien species.

The following lists the main ways of unintentional introduction, but some invasive organisms are not introduced through only one way, but may be introduced through two or more ways, not just once in time, but twice or more. The introduction of multi-channel and multi-frequency increases the possibility of colonization and diffusion of alien organisms.

Brought by human transportation

Many alien species enter and spread along the traffic routes, and the vegetation around highways and railways is usually destroyed and degraded, so these places are usually the earliest or most frequent places where alien species appear. For example, ragweed mostly occurs on both sides of railways and highways, and was originally introduced from North Korea by train; Rattus norvegicus and Rattus flavipectus in Xinjiang were also introduced from the mainland by railway.

Ship transportation

In the ocean, tens of thousands of species formed hundreds of millions of years later are limited by the external environment, such as the barrier between the oceans, the temperature difference and the low-salt estuary runoff, so many species can only live in a local sea area and become local species or native species in this sea area. There are also some creatures, because their adults or larvae swim or float, the transmission of ocean currents and tides, and the carrying of some animals (such as turtles, whales and seabirds), which have expanded their distribution and become widely distributed species. However, some transfers are related to the transportation of human ships.

The transportation mode is mainly through the discharge of ballast water in different places. Ballast water usually comes from the coastal waters of the ship's port of origin or route. It is estimated that ships transfer as much as 654.38 billion tons of ballast water every year in the world. Therefore, many bacteria, animals and plants are also inhaled and moved to the next port of call. There are about 16 species of harmful red tide organisms in China's coastal areas, most of which are mainly spread in the global coastal waters through ballast water. Exotic red tide species have aggravated the occurrence of red tide in coastal areas of China [3]. Another way of introduction by ship is to attach living organisms (such as barnacles) to the ship and bring them into new areas. After the introduction of these exotic creatures, some species fundamentally destroyed or changed the original ecological characteristics. For example, the carnivorous red snail (Rapana Thomas iana) migrated from the Sea of Japan to the Black Sea in 1947. After ten years, the oysters on the Black Sea Taota beach were almost completely eliminated.

The biological propagules loaded on the ship may sometimes be discarded, or escape after the ship sinks and rush out of the coast with the waves. Kalanchoe spathulata and aloe vera, which grow on some uninhabited islands in the East China Sea and South China Sea of China, may be discarded by early seagoing ships.

Marine garbage

With the floating of waste plastics and other man-made garbage, marine life is invading Antarctica and some tropical islands, posing a threat to local species. These wastes have increased the number of organisms spread to subtropical areas by 1 times, and even increased by more than 2 times in high latitudes. Compared with natural floating objects such as coconut or wood, marine life prefers to float on plastic containers and other non-degradable garbage. With these carriers, they can float almost anywhere in the world.