巨嘴鸟：森林演变的关键所在

by Christopher Joyce

Walking through the Atlantic coastal forests of Brazil in the morning is like eavesdropping[偷听] on a toucan[巨嘴鸟] symphony[交响曲]. Each produces its own unique sound to cut through the auditory[听觉的] clutter[混乱]. But over the past century， the toucans have been disappearing. Hunting， farming， logging[伐木]—its all taken a big toll[产生负面影响] on toucans.

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

According to research in the journal Science， this is what happened. The dominant[占优势的] palm tree depends on birds to eat its fruit and then defecate[通便] the seeds somewhere， so it will germinate[发芽] 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[过程].

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[弹球]， 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[从遗传学角度] disposed[处理] to make small seeds did just fine； in fact， they thrived[茁壮成长] and started to dominate[占优势] the forest. Galetti： The extinction[灭绝] of large birds changed the evolution of this palm.

Now， humans have always been messing with[干扰] 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[改变] the genetic makeup[组成] 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[预言] that climate change will make parts of Brazil hotter and drier， so much so that these palms could be in trouble.

Galetti： The impacts[冲击] on the forest can be quite dramatic[戏剧性的] because several animal species[种类] depends， rely on this palm for food.

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

晨间在巴西的大西洋沿岸森林中漫步，就像无意中听见巨嘴鸟的交响乐一样。每一只巨嘴鸟都有自己独特的叫声，在嘈杂纷繁的大合奏当中清晰可辨。但是在过去一个世纪以来，巨嘴鸟的数目不断减少。人类的猎杀农耕以及大肆伐木都对巨嘴鸟产生了极大的危害。

随着鸟群不断缩减，巨嘴鸟大合唱逐渐变成了呢喃细语。林中各处如今都看不见它们的身影了。而巨嘴鸟的消失似乎触发了森林本身的演变——尤其体现在棕榈树（的变化）上。

《科学》杂志上的研究指出，事情是这样的：大多数棕榈树依赖鸟类吞食果实，随后在其他地方将种子排出，这样种子就能（在别的地方）发芽生根，长成一棵新的树苗。

莫罗·加莱蒂是巴西圣保罗州立大学的生物学家。他说巨嘴鸟在这个繁衍过程中充当了非常重要的角色。

莫罗·加莱蒂：这些大型鸟类在森林当中占据着相当重要的地位，因为它们不仅传播种子，传播的还是大颗的种子。

最大的棕榈树种子有些大如弹珠，大多数鸟类无法下咽，只有巨嘴鸟可以吞下去。所以随着巨嘴鸟的消失，出产大种子的棕榈树就不走运了——它们失去了播种者。与此同时，那些在遗传上更容易长出小种子的棕榈树则一切如常；事实上，它们生机勃勃地壮大起来，开始逐步占领森林。

加莱蒂：大型鸟类的灭绝改变了这种棕榈树的演化过程。

人类向来对大自然肆意妄为。当我们不断砍伐森林，破坏草原，或者过度捕猎，我们就会改变（当地的）动植物构成。不过在这个例子当中，仅仅是一个无意的行为，人类便在一百年间改变了一个国家的野生棕榈树群的遗传结构。

如果这些小种子棕榈树彻底占领了森林，那会发生什么事情呢？事实上，小种子并不好。它们在干燥酷热的天气里容易干瘪，寿命更短。科学家预言，由于气候变化，巴西多处将会变得更加炎热，更加干燥，这种剧烈的变化将会给这些棕榈树带来极大的麻烦。

加莱蒂：森林（系统）可能会受到很严重的影响，因为棕榈树是好几种动物的食物来源。

事实上，（这将影响到）将近60种动物。所以（这件事的）实际结论就是：巨嘴鸟没了，森林也没了。