生物多樣性小百科

島嶼生物地理學

　　「島嶼生物地理學」是1967年由E.O.Wilson和R. MacArthur發展出來的。他們認為島嶼內物種的數目，會因物種滅絕的速度和出現的速度而影響。在一個全新的島嶼，物種會不斷從最近的大陸遷徙過來；到島嶼呈現飽和狀態時，每加入一個新物種就會造成一次生態變動，有些先驅種（先到的種類）逐漸被後到者取代，這種先驅者滅絕，後到者取代的模式，會漸趨緩和，最後形成穩定的動態平衡。

島嶼生物學的兩個重點是：

1.距離大陸愈近，島嶼上的生物就愈多，因為遷入的物種會比滅絕的物種多。

2.島嶼愈大，島上生物愈多，因為可供生物棲息的地方多。

　　島嶼生態地理可以用來比較兩個大小不同，但與大陸相同距離的島嶼；或是大小相同，但距離不同的島嶼。經由比較可以推測島嶼的形成年齡、遭受破壞的程度等。

  　島嶼生態地理學不只是應用在真正的島嶼，在陸地上的大小湖泊，甚至不同海拔的山峰都可以套用來計算生物多樣性。

Island Biogeography

Two eminent ecologists, the late Robert MacArthur of Princeton University and E. 0. Wilson of Harvard, developed a theory of "island biogeography" to explain such uneven distributions in 1967. They proposed that the number of species on any island reflects a balance between the rate at which new species colonize it and the rate at which populations of established species become extinct. If a new volcanic island were to rise out of the ocean off the coast of a mainland inhabited by 100 species of birds, some birds would begin to immigrate across the gap and establish populations on the empty, but habitable, island. The rate at which these immigrant species could become established, however, would inevitably decline, for each species that successfully invaded the island would diminish by one the pool of possible future invaders (the same 100 species continue to live on the mainland, but those which have already become residents of the island can no longer be classed as potential invaders).

The two main predictions of Island Biogeography are:
1. Islands close to a source area should have a higher number of species than islands further from the source area for islands of equivalent areas.
2. Larger islands should have more species than smaller islands for islands located at similar distances from the source area.

Island biogeography applies not only to islands, but can also be adapted to any series of discontinuous habitats such as forest fragments. Of course the theory of island biogeography has been expanded and refined since its earliest theoretical beginnings as outlined above.