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“慢活哲學”:樹懶的動作為什么那么慢?

更新時間:2019/10/12 20:15:42 來源:紐約時報中文網 作者:佚名

Why do sloths move so slowly?
“慢活哲學”:樹懶的動作為什么那么慢?

Sloths, as their name betrays, have little need to rush. For the most part, they live high in the branches of the forests which stretch across Central and South America, only coming down to the ground to defecate. And the life they lead is very much in slow motion.

樹懶,顧名思義,不需要太著急。在大多數情況下,它們生活在橫跨中美洲和南美洲的森林中,居住在樹枝上,只有排便時才會下到地面。它們的生活節奏非常緩慢。

Just why sloths move so slowly is due to some peculiar evolutionary tricks.

樹懶移動如此緩慢的原因是一些獨特的進化技巧。

Modern-day sloths – the three-toed sloth and the two-toed sloth – are much smaller versions of the sloths that inhabited the prehistoric world. Giant sloths, some that would weigh up to several tonnes, walked on the ground during the last ice age until around 11,000 years ago, foraging from the trees by standing up on their hind legs to reach into the foliage.

現代的樹懶——三趾樹懶和二趾樹懶,是史前世界里樹懶的更小版本。巨型樹懶,有些重達數噸,從上一個冰河時代直到大約11,000年前,它們一直在地面上行走,它們靠后腿站起來,把頭伸進樹冠,從樹上覓食。

“What changed was a combination of both going up into the trees, and having a diet almost entirely based on leaves,” says Camila Mazzoni of the Leibniz Institute for Zoo and Wildlife Research in Germany.

德國萊布尼茨動物園和野生動物研究所(Leibniz Institute for Zoo and Wildlife Research)的馬佐尼(Camila Mazzoni)說:“它們真正的改變是:一是爬到了樹上;二是飲食完全以樹葉為主。”

“The leaf diet is very poor in nutrients and the intake of calories is very low. Because of this they have to have a very slow metabolic rate to cope with this low calorific intake.”

她說:“樹葉類食物營養貧乏,卡路里的攝入量很低。因此,它們必須用非常慢的新陳代謝速度來應對低熱量的攝入。”

And part of that comes down to where it is they live.

還有部分原因在于它們居住的環境。

All six species of sloths live in tropical forests. It’s a hot and humid environment that means some of the normal advantages of an endothermic system aren’t really required – the environment’s already warm, so you don’t have to expend an enormous amount of energy to keep your muscles and cardiovascular system warm. So sloths don’t.

所有六種樹懶都生活在熱帶森林里。這是一個炎熱潮濕的環境,一些正常占優的吸熱系統功能并不真正需要——環境已經很溫暖了,樹懶也不需要花費大量的能量來保持肌肉和心血管系統的溫暖。

Being a mammal has its benefits. Capable of regulating their body temperature internally, they can live in colder climates – much colder than reptiles or other cold-blooded animals.

哺乳動物的好處是,它們可以調節體內溫度,能夠生活在寒冷的氣候中,比爬行動物或其他冷血動物更耐寒。

But this hot-blooded evolutional trick has a few drawbacks as well. In order to fuel this energy-hungry system, mammals need to eat a lot and often to keep the muscles needed for movement warm. It’s why mammals can still dart about on a cool day, while lizards remain sluggish – if they move at all.

但是這種熱血的進化技巧也有一些缺點。為了給這個高能量消耗的系統提供燃料,哺乳動物需要吃很多東西,而且經常需要運動來保持肌肉所需要的溫暖。這也是為什么哺乳動物在變冷的天氣里到處奔跑,而蜥蜴如果在移動的話卻行動遲緩。

This endothermic adaptation has allowed mammals to colonise most of the environments on Earth – including the freezing cold expanses of both poles.

這種恒溫性使得哺乳動物能夠在地球上的多種環境中生存,包括兩極冰冷的廣闊區域。

But elsewhere, some mammals have abandoned the endothermic traits that evolution has gifted them. In doing so, they’ve adopted a go-slow, energy-saving lifestyle more similar to cold-blooded animals.

但在有些地方,一些哺乳動物已經放棄了進化賦予它們的吸熱特性。在這個過程中,它們采用了慢節奏,更節能的生活方式,類似于冷血動物。

“The thermo-regulation that most mammals have to do requires a lot of energy,” says Mazzoni. “But because sloths don’t have it, it means they require a lot less energy.

馬佐尼說:“大多數哺乳動物,需要大量的能量來進行體溫調節。但樹懶沒有這種調節能力,所以它們需要的能量很少。”

“But this means they can only live in the tropics, and not high up in the mountains where the temperature gets quite low. Having said that, the two-toed sloth is a bit more flexible, and will go a bit higher into the mountains in Costa Rica.”

“但這也意味著樹懶只能生活在熱帶地區,而不能生活在氣溫較低的高山地區。雖然如此,但兩趾樹懶要靈活一些,而且會爬到哥斯達黎加更高一些的山上。”

The sloths’ tree-based life cycle means they spend very little time at risk from predators like the jaguar. This is another reason why lightning-fast reactions – and the enormous amount of energy needed to fuel them – just aren’t needed. “They have this intimate relationship with the trees,” says Mazzoni. “They depend on them.”

樹懶以樹為生活根基,使它們很少受到美洲虎等食肉動物的威脅。這也是樹懶為什么不需要閃電般快速的反應,以及為調節體溫所需要的大量能量的另一個原因。馬佐尼說:“樹懶與樹木有著親密的關系,并依賴它們而生存。”

She says sloths often “go up to the top of the canopy in the morning to get some energy from the Sun and when it gets really hot they go back down to the shade of the trees”. This behaviour is much more typical of cold-blooded animals – lizards and other reptiles – than it is of other mammals.

她說:“樹懶經常在早上爬到樹冠頂部,從太陽那里獲取一些能量,當天氣非常熱的時候,它們會回到樹蔭下”。這種行為,在蜥蜴和其它爬行類冷血動物身上表現得更為典型,在哺乳動物身上比較少見。

Becky Cliffe, a British zoologist who works at Costa Rica’s Sloth Conservation Foundation, says it is only when you see sloths in the wild that you truly appreciate just how slow they are. “You know they move slowly, but then you look at one and every part of their body – when they turn their head, or even when they blink – it’s all done so slowly. You have to spend a lot of time out in [the] field to see one.”

在哥斯達黎加樹懶保護基金會(Sloth Conservation Foundation)工作的英國動物學家克利夫(Becky Cliffe)說,只有當你在野外看到樹懶時,才能真正體會到它們的行動有多慢。“你知道它們移動得很慢,但是當你看到它們身體的每一個部位——它們轉頭的時候,甚至眨眼的時候都是很慢的。你必須花很多時間到野外去看。”

Look closely at a sloth and its fur will often also have a green shade to it. It might be tempting to assume that the animals have become so sedentary that they have become home to moss and algae from the trees around them. But this misses something far more fascinating, says Mazzoni.

仔細觀察樹懶,它的皮毛通常有綠色的陰影。人們可能會很容易認為,這些動物吊在樹上不動,以至于它們成了周圍樹上苔蘚和藻類的家園。但馬佐尼認為,這忽略了一些更有趣的東西。

“Their hair is modified and has these kind of openings in which the algae and fungi can grow,” she says. “It’s not because they’re slow. We know there’s some kind of symbiotic relationship going on there.”

她說:“它們的皮毛是經過改進的,天生有縫隙,藻類和真菌可以在其中生長。這并不是因為它們行動遲緩,而是存在某種共生關系。”

What are these algae good for? Many scientists are trying to figure that out. “It could be that it’s good for the sloths’ camouflage,” adds Mazzoni. The green algae and fungi could help sloths blend in to the background of the forest canopy.

這些苔蘚或藻類有什么用?許多科學家正試圖弄清楚這一點。馬佐尼補充說:“這可能對樹懶的偽裝有好處。”綠藻和真菌可以幫助樹懶融入森林樹冠的背景。

“It could also be a way for the sloths to get extra protein,” she says, noting that sloths have sometimes been seen to lick the algae growing on their fur. The fungal growths may also help keep down the number of parasites. “Their fur is almost completely water resistant, and impedes a lot of parasites. Sloths have fewer parasites than other mammals of a similar size.”

她說:“這也可能是樹獺獲取額外蛋白質的一種方式。”樹獺有時會舔食生長在它們皮毛上的藻類。真菌的生長也有助于減少寄生蟲的數量。她指出:“它們的皮毛幾乎完全防水,并能阻擋許多寄生蟲。樹懶身上的寄生蟲要比體型相似的哺乳動物少。”

Among the other hallmarks of mammalian life that sloths have dispensed with is the amount of milk nursing mothers produce for their offspring.

樹獺已經喪失了哺乳動物的一些特征,其中之一就是哺乳樹懶為后代所產乳汁的數量。

“Sloth mothers don’t store large amounts of milk, so it just comes out drop by drop,” says Cliffe. The young attach themselves close to the nipple, and then feed as the milk dribbles out.

克利夫說:“樹懶媽媽不會儲存大量的乳汁,所以乳汁是一滴一滴地滴出來。”幼崽要緊貼著乳頭,然后在乳汁滴出來時吸食。

Cliffe’s years watching sloths in the Costa Rican jungle has given her much insight into their behaviour. “They don’t jump and they don’t run. But they do have the most incredibly strong arms. If a human and a sloth had an arms wrestle, the sloth would definitely win.” But the sloth’s legs – which aren’t needed for breakneck speed or even supporting their full weight most of the time – don’t have the same muscle mass.

克利夫多年來一直在哥斯達黎加叢林中觀察樹懶,她對樹懶的行為有深入的了解。“他們不跳也不跑。但它們擁有強壯的手臂。如果人類和樹懶來一場手臂比拼,樹懶絕對會贏。但是樹懶不需要高速度的奔跑,甚至不需要支撐全身的重量,它們的腿卻沒有相同肌肉的質量。”

The sloth’s steady-as-you-go approach to life shouldn’t be mistaken for laziness, however, says Cliffe. “They’re not lazy. The howler monkeys that live in the forests sleep for up to 18 hours a day, and the sloths only sleep for around 10.”

然而,克利夫說,樹懶這種“按兵不動”的生活態度不應該被誤認為是懶惰。“他們不懶惰。生活在森林里的吼猴每天要睡18個小時,而樹懶只睡10個小時左右。”

Had sloths not ended up living in a hot, humid environment covered in trees, they might be sprightlier, living at a quicker pace. But over countless generations they have arrived at a pace of life perfectly suited to their environment.

如果樹懶沒有最終生活在被森林覆蓋炎熱潮濕的環境中,它們可能會活潑一些,運動節奏也快一些。但是經過無數世代進化,它們已經達到了完全適合所處環境的生活節奏。

“They show that you don’t have to run around all the time trying to find food,” says Cliffe. “They’ve relaxed the whole system.”

克利夫說:“這表明,它們不必跑來跑去地尋找食物。它們放松了整個系統。”

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