入侵物种

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如果一个物种被人为引入一个其先前不曾自然存在过的地区，并具备了在无更多人为干预的情况下在当地发展成一定数量的能力，以至威胁到了当地生物的多样性成为当地公害，就可称之为入侵物种。

入侵物种(Invasive species)是引进物种的一个子集。

[编辑] 简介

虽然入侵物种经常被定义为被引进的并成为祸害的品种，但有些物种天生就能在特定的区域，在人类活动的影响下繁殖并成为当地的一个入侵品种。澳大利亚东南部的杂色澳洲喜鹊（Pied Currawong ）就是一个例子: 由于人类对当地景观的改变，使得杂色澳洲喜鹊的数量在20世纪急剧增长。杂色澳洲喜鹊捕食其他小型鸟类的雏鸟，使得该地区其他小型鸟类数量锐减。在夏威夷，一种称做＂'ae'ae＂的湿地植物（当地的Bacopa monieri )也被看成是一个有害物种---因为它们的快速增长覆盖了原本用做保护Hawaiian stilt (Himantopus mexicanus knudseni)的浅水塘,使得这些区域不再适合这种濒危鸟类的觅食. 当然，地球上所有的物种都有一个数量增减周期，一般来说这个都是在一定范围内进行波动的。这类变化一般是由环境上的各种因素变化导致，而其中以由人类活动所带来的地貌改变的影响显得最为突出。 Anthropogenic (human derived) alteration of an environment that enables expansion of a species into a geographical area where it had not been seen before could be described as invasive because the range expansion results in the species occurring where it was not before native. In essence, one must define "native" with care, as it refers to some natural geographic range of a species, and is not coincident with human political boundaries. Whether noticed increases in population numbers is sufficient reason to regard a native species as "invasive" requires a broad definition of the term—but it seems reasonable to consider that some native species in disrupted ecosystems can become "pests" and in that sense, invasive.

U.S. Executive Order 13112 (1999) defines "invasive species" as "an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health" (CEQ, 1999). Thus, the term is used to imply a sense of actual or potential harm, something that may not be true for all introduced species.

[编辑] 历史观点

[编辑] 案例

Although it is assumed that invasive species have been a problem since man has been around to carry them, modern invasive species science began with the work of Charles Elton called The Ecology of Invasions by Animals and Plants, which was first published in 1958. The next ground-breaking work dealing with the principles of invasions was Island Biogeography and Conservation Practice by Simberloff and Abele in 1976.

There are several classic accounts of introduced species that have been causing problems for many decades. The sea lamprey began to make its way up into the Great Lakes of North America when the St. Lawrence Seaway was completed in 1959, devastating the lake trout fishing industry. It continues to be a largely-controlled problem today, but costs millions in lamprecides, traps, physical barriers, and other control methods. More recently, zebra mussels have been accidentally introduced into the Great Lakes (probably in 1988), and have since caused significant alteration to the underwater environment.

兔子于19世纪被引入澳大利亚 and their devastation is ongoing in spite of the famous rabbit fences that were built along thousands of miles of territory with the futile intention of keeping them out. See Rabbits in Australia.

在台灣，福壽螺是最有名的入侵物種之一。原本從南美洲引進要做為食用螺類，但因口感不佳而被棄養丟於水溝，但反而開始大量繁殖，對於農作物造成危害。另外吳郭魚是從新加坡引進的，雖然是常見的食用魚類，但是放養於水庫、湖泊的吳郭魚由於攻擊性強，逐漸排擠其他水生動物的生存空間。

[编辑] 生物学控制

Asian Tiger Mosquito (Aedes albopictus), a species
introduced to the USA, here biting a human.

The often unsuccessful use of biological control provides another historical perspective of the introduced species problem. When rats overwhelmed seaports and became crop pests during the 1800s in some islands in the Pacific, mongoose were introduced to control them. The mongoose preferred to eat native species that were easier to catch than the invasive rats, and became invaders themselves.

Another early use of biological control of an invasive species was an astounding success. In 1868 cottony cushion scale (Icerya purchasi) was accidentally introduced to California in a shipment of nursery plants from Australia. The scale moved into citrus groves and became a major pest, actually killing trees. Since the scale is not a serious pest in Australia, a search began to discover why. In 1888 a naturalist observed Australian ladybirds (Rodolia cardinalis) eating the scale. American lady bugs had shown little interest in the insect. The Australian species was introduced to California, and within a year, the pest was controlled to economically insignificant levels.

Modern day biological control is used only if extensive studies find that the biocontrol species will not have a negative effect on native populations.