regularity--that about 10% (5%~20%) of introduced species become established and 10% of these become pests (Williamson & Fitter 1996)
Байду номын сангаас
外来种对生态系统健康的影响
• 外来种对生态系统造成危害的机制:
• arrived by transatlantic ship-an undetected stowaway in ballast water first (1985 or 1986) in Lake St. Clair, between Lakes Huron and Erie
• spread rapidly throughout lakes and waterways of the eastern United States and Canada, from the Great Lakes through the Mississippi River drainage.
Zebra mussel, Dreissena polymorpha
• History of invasion:
• Native to the Caspian and Black Seas, over the past 200 years, it has spread into northern Europe and is common in rivers, was discovered in North America in 1988
水生态系统中的入侵种－ "杀手藻"
• An invasive strain of the marine alga Caulerpa taxifolia ("killer algae") appeared in the
Mediterranean Sea in 1984, and is now rapidly covering thousands of acres of sea bed. It smothers and kills all native vegetation, and the animals that depended on that vegetation are displaced or die off. In the summer of 2000, the alga was discovered in Agua Hedionda Lagoon (San Diego County) and Huntington Harbor (Orange County). This plant could have a disastrous impact on the local ecology if it is not quickly eradicated. Legislation is being introduced to ban importation of the plant, which is used as a saltwater aquarium ornamental.
recent human activities, also called alien, introduced or nonindigenous species
• 美国, 自哥伦布踏上美洲大陆，估计有超过 30,000 中非本土物种被引进 (Pimentel et al., 2000)，
• 超过 4500 外来种在美国成功定居
– Exotics are a factor contributing to the endangered or threatened status of 42% of animals and plants on the U.S. endangered species list.
水生态系统中的入侵种－水葫芦
外来种
• 外来种（植物或动物）是指由于近期人类 活动而被引入到以前没有该物种存在的地 区的物种，也叫引进种或非土著种。An exotic species of plant or animal is one that was introduced into an area where it did not previously occur through relatively
– 改变生境 e.g. common carp – 竞争 – 捕食 e.g. Nile perch, sea lamprey – 引入病原体和寄生虫 – 遗传效应 genetic effects, caused by
interbreeding with native species.
• 在自然生态系统中，入侵种通常与本地种竞 争，取代本地种
Beach covered with zebra mussels
七鳃鳗 Sea Lamprey
Sea lampreys are native to the Atlantic Ocean. For many centuries, the lamprey's access to the Great Lakes was blocked by Niagara Falls. Then the Welland Canal was built in 1883, allowing the lamprey to enter Lake Erie. During the period from 1921 to 1940 it spread through the remainder of the lakes, feeding on several kinds of fish including the lake trout which had been the basis of a multi-million dollar fishing industry. The lamprey destroyed 97% of the trout population in the Great Lakes in this period. After many years of research, a poison was discovered (TFM or 3-trifluoromethyl-4-nitrophenol) that killed lamprey larvae but was not toxic to other fish. Over a two-year period (1960-62) the lamprey population was reduced by 85% but not eliminated. About 250 Great Lakes tributaries are now treated at regular intervals with the lampricide, and this method is being supplemented with barriers across streams to prevent the lampreys reaching their spawning grounds, and with release of sterilized males that reduce the number of fertile eggs laid by the females.
• Invasion of water systems by water hyacinth is a global problem. Enormous mats of the plant are growing along the shores of Africa's Lake Victoria, where the vegetation blocks the intakes of water treatment facilities and power plants, and interferes with access to boat docks. Kenya's government is contracting with an American company to try to remove the weed. The same weed is overwhelming Lake Malawi, home to the greatest number of fish species of any lake in the world.
• Two species of goby(鰕虎鱼 ) from the Caspian Sea have been introduced to feed on the mussels. But may itself cause further biological problems if it is widely distributed.
➢ shuting down electrical utilities by clogging water intake pipes, causing $5 billion in damages by the year 2002
➢ causing large-scale ecosystem changes and hastening the decline of our native freshwater mussels (50% decline in species in a decade)
• 但并不是所有外来种都有害：
– 事实上，有些种可以完成以前由已经稀有或灭 绝的土著种所担当的作用，这种情况下，清除 它们的理由不足
– 一些外来种引进了几个世纪，已归化，因此作 为外来种有争议
– 另外一些种类在全新世时期对气候的反应迁入 和迁出该地区，因此不能被认为是外来种
入侵种 Invasive species
• Native mollusk populations tend to crash within four years of zebra mussel colonization