巨嘴鳥：森林演變的關鍵所在

by Christopher Joyce

Walking through the Atlantic coastal forests of Brazil in the morning is like eavesdropping[偷聽] on a toucan[巨嘴鳥] symphony[交響曲]. Each produces its own unique sound to cut through the auditory[聽覺的] clutter[混亂]. But over the past century， the toucans have been disappearing. Hunting， farming， logging[伐木]—its all taken a big toll[產生負面影響] on toucans.

With fewer and fewer birds， the toucan symphony is down to a murmur[低語]. Theyre just about gone from many parts of the forest. And it appears that their disappearance kickstarted[（比喻）強勁推動] a whole evolutionary[進化的] change in the forest itself， particularly in its palm trees.

According to research in the journal Science， this is what happened. The dominant[占優(yōu)勢的] palm tree depends on birds to eat its fruit and then defecate[通便] the seeds somewhere， so it will germinate[發(fā)芽] and grow a new tree.

Mauro Galetti is a biologist at the Estadual Paulista University in Brazil. He says toucans play a big part in this reproductive[生殖的] process[過程].

Mauro Galetti： These large birds， they have an extremely important role in the forest not only because they disperse[散播] seeds， but because they disperse large seeds.

The largest palm seeds， some the size of marbles[彈球]， are too big for most birds to eat except for those big-mouthed toucans. So as the toucans disappeared， the palms that made big seeds were out of luck—no seed dispersers[分散器]. Meanwhile， the palms that were

genetically[從遺傳學角度] disposed[處理] to make small seeds did just fine； in fact， they thrived[茁壯成長] and started to dominate[占優(yōu)勢] the forest. Galetti： The extinction[滅絕] of large birds changed the evolution of this palm.

Now， humans have always been messing with[干擾] nature. When we cut down forests or prairie[大草原]， or when we over-hunt， we change the mix of plants and animals. But in this case，humans actually altered[改變] the genetic makeup[組成] of a wild palm tree population， in just a century， by accident.

So what happens if these small-seed palms eventually[最后] take over？ Well， it turns out that smaller seeds arent so good. They dry up and die faster in hot， dry weather. And scientists predict[預言] that climate change will make parts of Brazil hotter and drier， so much so that these palms could be in trouble.

Galetti： The impacts[沖擊] on the forest can be quite dramatic[戲劇性的] because several animal species[種類] depends， rely on this palm for food.

About 60 species of animals， in fact. So the take-home[實際得到的] message is： As the toucan goes， so goes the forest.

晨間在巴西的大西洋沿岸森林中漫步，就像無意中聽見巨嘴鳥的交響樂一樣。每一只巨嘴鳥都有自己獨特的叫聲，在嘈雜紛繁的大合奏當中清晰可辨。但是在過去一個世紀以來，巨嘴鳥的數(shù)目不斷減少。人類的獵殺農耕以及大肆伐木都對巨嘴鳥產生了極大的危害。

隨著鳥群不斷縮減，巨嘴鳥大合唱逐漸變成了呢喃細語。林中各處如今都看不見它們的身影了。而巨嘴鳥的消失似乎觸發(fā)了森林本身的演變——尤其體現(xiàn)在棕櫚樹（的變化）上。

《科學》雜志上的研究指出，事情是這樣的：大多數(shù)棕櫚樹依賴鳥類吞食果實，隨后在其他地方將種子排出，這樣種子就能（在別的地方）發(fā)芽生根，長成一棵新的樹苗。

莫羅·加萊蒂是巴西圣保羅州立大學的生物學家。他說巨嘴鳥在這個繁衍過程中充當了非常重要的角色。

莫羅·加萊蒂：這些大型鳥類在森林當中占據(jù)著相當重要的地位，因為它們不僅傳播種子，傳播的還是大顆的種子。

最大的棕櫚樹種子有些大如彈珠，大多數(shù)鳥類無法下咽，只有巨嘴鳥可以吞下去。所以隨著巨嘴鳥的消失，出產大種子的棕櫚樹就不走運了——它們失去了播種者。與此同時，那些在遺傳上更容易長出小種子的棕櫚樹則一切如常；事實上，它們生機勃勃地壯大起來，開始逐步占領森林。

加萊蒂：大型鳥類的滅絕改變了這種棕櫚樹的演化過程。

人類向來對大自然肆意妄為。當我們不斷砍伐森林，破壞草原，或者過度捕獵，我們就會改變（當?shù)氐模﹦又参飿嫵?。不過在這個例子當中，僅僅是一個無意的行為，人類便在一百年間改變了一個國家的野生棕櫚樹群的遺傳結構。

如果這些小種子棕櫚樹徹底占領了森林，那會發(fā)生什么事情呢？事實上，小種子并不好。它們在干燥酷熱的天氣里容易干癟，壽命更短?？茖W家預言，由于氣候變化，巴西多處將會變得更加炎熱，更加干燥，這種劇烈的變化將會給這些棕櫚樹帶來極大的麻煩。

加萊蒂：森林（系統(tǒng)）可能會受到很嚴重的影響，因為棕櫚樹是好幾種動物的食物來源。

事實上，（這將影響到）將近60種動物。所以（這件事的）實際結論就是：巨嘴鳥沒了，森林也沒了。