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作者：艾德•杭特
多虧人類在生物棲地的發展與侵擾，使得瀕臨絕種生物名單上從不短缺物種；就另一方面來說，一些生物卻因此從中獲利。事實上，一些動植物族群確實能在被人類干擾過的土地上成長茁壯。
誠如「舊金山紀事報」所提到，人類的行為造就了黑熊、白尾鹿、土狼、紅狐、鵝、臭鼬及貓頭鷹的「黃金年代」。
紀事報的格林•瑪汀寫到：「若野生物種不被滅絕算是得分的話，那當然得分越多越好，若確實是因為人類行為破壞棲地而得分（指某些物種的繁盛）的話，那真要謝謝你了」；「就生態學的說法，棲地被侵擾意指人類在野地上伐木、農業耕作或部分開發。這樣的情形對某些動物而言代表著死亡，卻是其他動物的大好機會。」
人類的行為幫助了鹿、熊及土狼的數量大幅增加，並且散佈在經過林木砍伐、土壤耕種或郊區化後面積大增的棲地上。有些物種無法適應如此的棲地改變，但是另一些「機會主義」的物種確有絕佳的適應性。他們沒有天敵及競爭者，對棲地及食物不太挑剔，所以能夠快速繁殖。
科學家說當棲地被侵擾，整個區域的生物量也許不會改變，但通常生物多樣性會下降。
加州柏克萊大學環境科學政策管理系主任，生物保育教授史蒂芬•賓辛格爾說：「根據觀察，我們發現一個情況：在棲地被干擾之後，當能夠適應這種環境的物種擴散至全球時，世界各地的動物相也正逐漸地被同質化了。」
這種適應能力使得這些「浪跡天涯型」的物種成為各地的入侵種。人們除了刻意將之引進某些地區，人類的某些活動無異於敞開大門整理好環境在歡迎牠們進駐。
美國東岸的紐約時報這個星期同時有一篇報導指出，部分的科學家認為，並非所有被引進的物種都是問題。每年雖然花費數百萬美元在消滅非原生物種以及防止引進新的物種；非原生物種的入侵卻正是全世界生物多樣化的最大威脅，僅次於棲地破壞的影響。
然而，一些進化論的生物學家正在辯論：「外來種與原生種之間的差別，是人為定義的」，並且認為應將注意力集中在少數會嚴重危害生態系的引進種。另一些學者則針對「被人類引進之入侵種改變的生態系是否比較不自然」的問題提出質疑。一位科學家甚至懷疑，入侵種是否真的會造成生物多樣性的降低，因為，終將會有新的物種來取代那些被外來入侵種趕走的原生物種。
不過，另有其他科學家警告說，「我們可能會因為沒有證據顯示其負面影響，而以為外來種是可被接受的。非原生物種可能在起初幾十年間看似無害，後來卻轉變成極具侵略性。」
目前，動物權與環保團體正與企圖控制、防止或消滅入侵種的人士抗爭。期望這場抗爭能突顯在有關入侵種之議題當中對於「萬物共榮共存」的詮釋。(2001.09.07)
相關資料：
有些動物在被人類干擾的棲地上勝出 http://www.sfgate.com/cgi-bin/article.
cgi?f=/c/a/2001/09/03/
MN226317.DTL
有些外來種動物很安份，有些卻製造了麻煩
http://www.nytimes.com/
2001/09/04/science/life/04EXOT.html
EbbTIDE是由Tidepool編輯艾德•杭特主筆，發表在Tidepool有關生態趨勢的每週評論。
全文與圖詳見：http://www.tidepool.org/ebbtide/ebb9.
07.01.cfm
版權歸屬Tidepool，環境資訊協會(鄧國光 譯，吳海音 審校)
中英對照全文：http://e-info.org.tw/issue/animal/2001/
issue-animal01092601.htm |
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[SEPTEMBER.07.02001] by edHUNT
There's no shortage of species on the slated for extinction thanks to our development and encroachment on their habitat. On the other hand, there are some species that take advantage of habitat after it has been disturbed. In fact, some plants and animals actually thrive in human disturbed habitats.
As the San Francisco Chronicle reported this week -- human activity has made it a "Golden Age" for species like the black bear, white tailed deer, the coyote, red fox, geese, skunk and the barred owl.
"While it's true that scores of wild species are flirting with extinction, scores more are doing just fine, thank you - and for precisely the same reasons, " the Chronicle's Glen Martin wrote. " The fate of both groups hinge on "disturbed" habitats, an ecologist's term for wildlands that have been logged, farmed or partially developed. For many animals, disturbance equals death. For others, it is an opportunity to excel."
Human activity has helped deer, bear and coyote populations to swell and spread into habitat that offered them little before it was logged, farmed or suburbanized. While some species have trouble adapting to habitat changes, these opportunistic species are very adaptable. They reproduce quickly, lack predators and competitors and are generalists in terms of habitat and diet.
Scientists say that when habitat is disturbed, the overall biomass that a given amount of land can support may not change, but the biodiversity is often lost.
"One of the things we're seeing is the homogenization of fauna the world over as certain species adapt to disturbed conditions across many continents," said Steven Beissinger, professor of conservation biology and chairman of the Department of Environmental Science Policy and Management at the University of California at Berkeley.
This adaptability sort of makes these "tramp" species like invasive species. Except instead of being directly introduced by human activity, human activity just opens the door and fluffs the pillows for them.
ON THE OTHER SIDE OF THE CONTINENT, the New York Times ran an article this week reporting that some scientists are arguing that not all introduced species are a problem. Billions of dollars each year are spent on rooting out nonnative organisms and preventing the introduction of new organisms. Next to habitat destruction, the invasion of nonnative species represent the greatest threat to biodiversity world wide.
However, some evolutionary biologists are now arguing that "distinctions between exotics and native species are artificial," and that more effort should be focused the small number of introduced species that cause real problems for an ecosystem. Others question whether an ecosystem altered by a human-introduced invasive species should be considered "less natural" than one that hasn't. One scientist even questions whether invasive species reduce biodiversity, since new species will eventually come in to replace those pushed out by the exotic intruder.
Other scientists caution, however, that exotic species can seem acceptable "only because no one has documented their harmful effects. And nonnative species can appear innocuous for decades, then turn invasive."
Expect the live and let live interpretation of this argument to show up as some animal rights and environmental groups fight attempts to control, prevent, or eradicate invasive species.
WORTH READING:
Some Animals Excel in Disturbed Habitat http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2001/09/03/MN226317.DTL
Some Alien Species Fit In Fine, Some Cause Trouble
http://www.nytimes.com/2001/09/
04/science/life/04EXOT.html
ebbTIDE is a weekly comment on the bioregional news featured in Tidepool and written by Tidepool Editor
Ed
Hunt.
http://www.tidepool.org/ebbtide/ebb9.07.
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