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Alien plants and animals are not all bad.
外來入侵動植物不都是有害的。
Introduced species have a bad rap.
外來引進物種的名聲很差。
From American grey squirrels displacing European red ones, to Japanese knotweed displacing just about everything everywhere, their purported negative effects on nature are there for all to see.
從美州灰松鼠取代歐洲紅松鼠，到日本虎杖取代英國幾乎所有本土植物，外來物種對自然造成的負面影響是有目共睹的。
But it is only the human eye which prefers the arboreal rodents in a particular place to be red rather than grey.
但希望在某個特定地點，樹上住著紅色嚙齒動物，而不應該是灰色嚙齒動物的，實際上只有人類。
Ecologically, both occupy the same niche.
從生態角度看，灰松鼠和紅松鼠占據著相同的生態位。
Nor might people fret about knotweed growing at other plants’ expense if it did not also undermine human constructions such as buildings and roads.
人們也無需擔心虎杖以其他植物消失為代價生長，只要它不會破壞建筑物和道路等人類建筑。
Until the middle of the 20th century, moving species around the world was reckoned a normal, often valuable, thing to do, while the consequences of their accidental movement were rarely considered.
到20世紀中葉以前，人們一直認為物種在世界各地的遷徙是一件正常的、并且通常極具價值的事情，而很少考慮它們偶然遷徙造成的后果。
It was not until the publication in 1958 of “The Ecology of Invasions by Animals and Plants”, by Charles Elton, one of the founders of scientific ecology, that values began to change.
直到1958年，科學生態學的創始人之一查爾斯·埃爾頓出版了《動植物入侵生態學》一書，人們的觀念才開始發生變化。
Conservation is, as the name implies, a conservative business.
保護，顧名思義，在于保守。
Those involved often value “nativism” - the idea that the species mix in a particular place should remain as unchanged as possible.
參與動植物保護的人往往會堅持“本土主義”，即特定地點不同物種的組合應該盡可能保持穩定。
But this is just an opinion.
但這動植物保護的觀點之一。
Other opinions are possible.
還有其他一些可能的觀點。
A study published recently in Trends in Ecology & Evolution by Dov Sax of Brown University, in Rhode Island, thus asks how the benefits of introduced species might be better assessed, so that opinions can be more informed.
羅德島州布朗大學的多夫·薩克斯近期在《生態學與進化趨勢》上發表的一項研究提出了如何更好地評估引進外來物種的好處，為外來物種能夠帶來好處的觀點提供依據。
Specifically, he and his compadres have recruited the vocabulary of moral philosophy.
具體地說，他和他的團隊利用了道德哲學領域的詞匯。
They thus identify three sets of reasons why an introduced species might be valuable: instrumental, intrinsic and relational.
他們據此確定了外來物種可能具有的三種價值：工具價值、內在價值和關系價值。
Instrumental values are easiest to grasp.
工具價值是最容易理解的。
They pertain to things that provide direct human advantage.
人類能夠直接從具有工具價值的事物中獲取利益。
Dr Sax and his colleagues ignored crops, since these are heavily managed by human beings and their benefits are obvious.
薩克斯博士和他的同事沒有考慮農作物，因為農作物在很大程度上是由人類進行管理的，它們帶來的好處是顯而易見的。
But they included transplanted grass species that have gone wild, yet provide grazing for stock animals, and introduced forest trees that yield timber for construction.
但他們研究了移植后開始大量生長，可以作為牲畜飼料的草種，以及引入的可用于生產建筑用木材的林木。
One little-regarded but important example of instrumental value is the transport of Old World earthworms to North America, parts of which were left worm-free after the last ice age.
工具價值有一個鮮為人知但十分重要的例子，即舊世界蚯蚓入侵北美，自上一個冰河時代后到蚯蚓入侵之前，北美的一部分地區完全沒有過蚯蚓的存在。
The presence of these is reckoned to have increased agricultural productivity by as much as 25% in previously worm-deprived areas, though recent work suggests other invertebrates have suffered.
據估計，蚯蚓的出現讓以前沒有蚯蚓的地區農業生產率提高了25%，但最近的研究也表明，其他無脊椎動物受到了蚯蚓入侵的影響。
Honeybees, too, are an Old World species introduced into the New.
蜜蜂也是從舊世界引入新世界的物種。
Their instrumental benefits in the form of honey and wax are obvious.
它們的蜂蜜和蜂蠟具有明顯的工具價值。
But they also pollinate flowering plants, including many crops.
此外，它們也為開花植物，包括許多農作物授粉。
Honeybees’ role as pollinators also makes them pertinent to the second category, intrinsic values.
蜜蜂作為傳粉者的角色也使它們與外來物種的第二種價值——內在價值——相關。
These pertain to the ecosystem into which the introduction has happened.
內在價值與物種引入的生態系統有關。
Since honeybees pollinate wild plants as well as domesticated ones, they have a positive intrinsic effect on their adopted habitats.
由于蜜蜂既為野生植物授粉，也為栽培植物授粉，它們對引入后的棲息地具有積極的內在影響。
Introduced species can bring other benefits.
引進的外來物種還具有其它好處。
Sometimes, in a manner reminiscent of the nursery rhyme in which an old lady swallows a fly, a spider to catch it, and a bird to catch the spider, an introduction may be made to undo a previous harm.
有時，外來物種的引進能讓我們聯想到一個童謠：老婦人吞下了一只蒼蠅，又吞下一只蜘蛛去抓蒼蠅，然后又吞下一只鳥去抓蜘蛛——引入外來物種或許能夠消除該地此前受到的傷害。
Several introductions of damaging insects have been attacked successfully by further introductions of critters that eat them - though this has not worked so well for voracious introduced molluscs called giant African land snails.
一些地區已經通過引入其它生物成功地攻擊了此前入侵此地的害蟲——盡管這對消滅貪吃的非洲大蝸牛這種軟體動物來說沒什么作用。
