本篇文章共分 4 段，從太平洋島嶼的地理概況到這些島嶼上生命的起源以及其後的演化與大陸生態系統不同之處分別加以說明。

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Pacific Ecosystems 太平洋生態系統

1. 太平洋島嶼概況

   The Pacific Ocean accounts for one-third of Earth’s surface and half of the world’s ocean area. It has about 25,000 islands, of which about 7,500 are oceanic, being relatively far from a continental shore. The great majority of all Pacific islands were born barren of life; hard, dense, volcanic rock pimples on the sea’s surface. New Zealand is the chief exception. It is among the continental islands of the western Pacific, together with Fiji, the Solomons, and others to the west.

   太平洋佔地球表面的三分之一，占世界海洋面積的一半。它有大約 25,000 個島嶼，其中約 7,500 個是海洋性的，離大陸海岸相對較遠。所有太平洋島嶼中的絕大部分生來就沒有生命，是海面上堅硬、密集的火山岩小丘。紐西蘭是一個主要的例外。它與斐濟、所羅門群島以及西邊的其他島嶼一起，屬於西太平洋的大陸島嶼。

2. 島嶼的生命來源

   Life arrived on most other islands by accident or by drift. Some plants arrived by air transport; seeds carried in the digestive tracts of birds account for nearly 40 percent of Hawaii’s early plants. The first invaders were either creatures that could float well enough, in air or water to cross stretches of ocean, or those whose seeds could survive a voyage in some bird’s gut. At times of lower sea level, land bridges linked, or nearly linked, many islands in the far western Pacific, so some species colonized these islands without being notably good floaters or stowaways. In the eastern Pacific (Easter Island, for example) only the best floaters and travelers arrived and survived. Consequently, the western islands have far more species and far greater biodiversity than do the eastern islands of Polynesia. Mammals found it hard to get anywhere in the island Pacific, only bats and rats successfully colonized east of New Guinea. Almost all species derive from Asia, the early Pacific was an Asian lake, with only a tiny proportion of species from the Americas. As a rule of thumb, the further from Indonesia, the more impoverished the plant and animal life and, in consequence, the less stable and resilient in the face of disturbance. This attenuation is strong for land species, less strong for marine species, and nonexistent for oceanic birds although fairly strong for land birds.

   其他大多數島嶼上的生命是通過意外或漂流到達的。一些植物通過空運到達；鳥類消化道攜帶的種子占夏威夷早期植物的近40％。最早的入侵者要麼是能夠在空中或水中漂浮得足夠順利的生物，要麼是那些種子能夠在鳥類的腸道中生存下來的生物。在海平面較低的時候，陸橋將遠在西太平洋的許多島嶼連接起來，或幾乎連接起來，因此一些物種在這些島嶼上殖民，而不需要有優良的漂浮或偷渡能力。在東太平洋（例如復活節島），只有最優秀的漂浮者和旅行者到達並存活下來。因此，西部島嶼的物種比波利尼西亞東部島嶼多得多，生物多樣性也大得多。哺乳動物看起來很難到達任何太平洋島嶼，只有蝙蝠和老鼠成功地在新幾內亞的東部定居下來。幾乎所有的物種都來自亞洲，早期的太平洋是一個亞洲湖泊，只有極小部分的物種來自美洲。根據經驗，離印尼越遠，植物和動物的生命就越貧乏，因此，在面對干擾時的穩定性和適應性就越差。這種衰減對陸地物種很明顯，對海洋物種則不那麼顯著，對海洋鳥類不存在，但對陸地鳥類相當明顯。

3. 島嶼的生態脆弱原因之一

   Pacific ecosystems evolved in relative (but differential) isolation from the continental crucibles of biological evolution. This meant opportunities for speciation – the development of new species occupying ecological niches elsewhere – were already filled. The finches described by the naturalist Charles Darwin on the Galapagos Islands – birds that divided into different species, each specialized for a narrow niche – are the classic example. On islands that had no mammals, reptiles and birds took their place. Thus, the Galapagos have giant tortoises, and New Zealand once had giant birds that functioned more or less like browsing or grazing mammals. Throughout most of the Pacific, the paucity of grazing animals meant that plants developed no defenses, such as spines, poisonous chemicals, or bitterness. The remote islands had a very high proportion of endemism – that is, of species that existed only there. In the case of Hawaii, as many as 99 percent of the species were endemic. All this led to a certain biological vulnerability among the terrestrial island species, should they ever be obliged to compete for niche space with the winners of the more intense continental competitions for survival. This vulnerability increased toward the east and toward the remote corners of the Pacific along a gradient defined chiefly by the degree of isolation.

   太平洋的生態系統是在與生物進化的大陸熔爐相對（但有區別）隔離的情況下進化的。這就意味著物種形成的機會—亦即在其他地方佔據生態利基的新物種發展—已經被填補。自然學家查爾斯．達爾文在加拉帕戈斯群島上描述的雀鳥—分為不同的物種，每個物種都專門擁有一個狹窄的利基—是個典型的例子。在沒有哺乳動物的島嶼上，爬行動物和鳥類取代了它們的位置。因此，加拉帕戈斯群島有巨龜，新西蘭曾經有巨鳥，其功能或多或少類似於啃食或放牧的哺乳動物。在整個太平洋的大部分地區，放牧動物的稀少意味著植物沒有發展出任何防禦措施，如刺、有毒的化學物質或苦味。偏遠的島嶼有非常高的地方性比例—也就是說，只有那裡才有的物種。就夏威夷而言，多達 99％ 的物種是地方性的。所有這一切導致了陸地島嶼物種的某種生物脆弱性，萬一它們有一天不得不與更激烈的大陸生存競爭中的勝利者競爭利基空間的話。這種脆弱性沿著主要由隔離程度決定的梯度向東和向太平洋的偏遠角落增加。

4. 島嶼的生態脆弱原因之二

   A second source of vulnerability, perhaps more decisive, arose from the arrival of humankind in the Pacific. Island animals evolved with no experience of the ways of humankind or indeed of any large terrestrial predators. As a result, they had no immunities to the predators or the effects of human action. Pacific animals were often unwary and easy prey. At the extreme, again the Galapagos, Darwin found many birds almost tame, so naively trusting that they would allow him to get within arm’s reach. Pacific plants had little experience with fire, because natural fires were very rare, except in a few places. Thus, few plants were well adapted to fire and most proved vulnerable to it. In contrast, continental species that had evolved in the presence of humankind or in places where natural fire is much more common, could recover easily after burns, and some could flourish as a result of fire. In short, Pacific ecosystems were different from continental ones on account of their isolation. They were well adapted to their circumstances but very vulnerable to alien invasion and human impact.

   脆弱性的第二個來源，也許更具有決定性，來自於人類來到了太平洋。島上的動物在進化過程中沒有經歷過人類的方式，也沒有經歷過任何大型的陸地捕食者。因此，它們對捕食者或人類行為的影響沒有免疫力。太平洋上的動物往往沒有警惕性，容易成為獵物。在極端的加拉帕戈斯群島，達爾文發現許多鳥類幾乎是馴服的，它們是如此天真地信任，以至於讓他近在咫尺。太平洋地區的植物對火沒有什麼經驗，因為自然之火非常罕見，除了少數地方之外。因此，很少有植物能輕鬆地適應火災，而且大多數植物被證明很容易受到火災的影響。相比之下，在有人類存在的地方或在自然之火更常見的地方進化的大陸物種，在火焚之後很容易恢復，有些還能因火而繁榮。簡而言之，太平洋的生態系統因其與世隔絕而不同於大陸的生態系統。它們能優秀地適應自己的環境，但非常容易受到外來入侵和人類的影響。