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“慢活哲学”:树懒的动作为什么那么慢?

更新时间:2019/10/12 20:15:42 来源:纽约时报中文网 作者:佚名

Why do sloths move so slowly?
“慢活哲学”:树懒的动作为什么那么慢?

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.

树懒,顾名思义,不需要太着急。在大多数情况下,它们生活在横跨中美洲和南美洲的森林中,居住在树枝上,只有排便时才会下到地面。它们的生活节奏非常缓慢。

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

树懒移动如此缓慢的原因是一些独特的进化技巧。

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.

现代的树懒——三趾树懒和二趾树懒,是史前世界里树懒的更小版本。巨型树懒,有些重达数吨,从上一个冰河时代直到大约11,000年前,它们一直在地面上行走,它们靠后腿站起来,把头伸进树冠,从树上觅食。

“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.

德国莱布尼茨动物园和野生动物研究所(Leibniz Institute for Zoo and Wildlife Research)的马佐尼(Camila Mazzoni)说:“它们真正的改变是:一是爬到了树上;二是饮食完全以树叶为主。”

“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.”

她说:“树叶类食物营养贫乏,卡路里的摄入量很低。因此,它们必须用非常慢的新陈代谢速度来应对低热量的摄入。”

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

还有部分原因在于它们居住的环境。

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.

所有六种树懒都生活在热带森林里。这是一个炎热潮湿的环境,一些正常占优的吸热系统功能并不真正需要——环境已经很温暖了,树懒也不需要花费大量的能量来保持肌肉和心血管系统的温暖。

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.

哺乳动物的好处是,它们可以调节体内温度,能够生活在寒冷的气候中,比爬行动物或其他冷血动物更耐寒。

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.

但是这种热血的进化技巧也有一些缺点。为了给这个高能量消耗的系统提供燃料,哺乳动物需要吃很多东西,而且经常需要运动来保持肌肉所需要的温暖。这也是为什么哺乳动物在变冷的天气里到处奔跑,而蜥蜴如果在移动的话却行动迟缓。

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

这种恒温性使得哺乳动物能够在地球上的多种环境中生存,包括两极冰冷的广阔区域。

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,一些哺乳动物已经放弃了进化赋予它们的吸热特性。在这个过程中,它们采用了慢节奏,更节能的生活方式,类似于冷血动物。

“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.

马佐尼说:“大多数哺乳动物,需要大量的能量来进行体温调节。但树懒没有这种调节能力,所以它们需要的能量很少。”

“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.”

“但这也意味着树懒只能生活在热带地区,而不能生活在气温较低的高山地区。虽然如此,但两趾树懒要灵活一些,而且会爬到哥斯达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.”

树懒以树为生活根基,使它们很少受到美洲虎等食肉动物的威胁。这也是树懒为什么不需要闪电般快速的反应,以及为调节体温所需要的大量能量的另一个原因。马佐尼说:“树懒与树木有着亲密的关系,并依赖它们而生存。”

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.

她说:“树懒经常在早上爬到树冠顶部,从太阳那里获取一些能量,当天气非常热的时候,它们会回到树荫下”。这种行为,在蜥蜴和其它爬行类冷血动物身上表现得更为典型,在哺乳动物身上比较少见。

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.”

在哥斯达黎加树懒保护基金会(Sloth Conservation Foundation)工作的英国动物学家克利夫(Becky Cliffe)说,只有当你在野外看到树懒时,才能真正体会到它们的行动有多慢。“你知道它们移动得很慢,但是当你看到它们身体的每一个部位——它们转头的时候,甚至眨眼的时候都是很慢的。你必须花很多时间到野外去看。”

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.

仔细观察树懒,它的皮毛通常有绿色的阴影。人们可能会很容易认为,这些动物吊在树上不动,以至于它们成了周围树上苔藓和藻类的家园。但马佐尼认为,这忽略了一些更有趣的东西。

“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.”

她说:“它们的皮毛是经过改进的,天生有缝隙,藻类和真菌可以在其中生长。这并不是因为它们行动迟缓,而是存在某种共生关系。”

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.

这些苔藓或藻类有什么用?许多科学家正试图弄清楚这一点。马佐尼补充说:“这可能对树懒的伪装有好处。”绿藻和真菌可以帮助树懒融入森林树冠的背景。

“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.”

她说:“这也可能是树獭获取额外蛋白质的一种方式。”树獭有时会舔食生长在它们皮毛上的藻类。真菌的生长也有助于减少寄生虫的数量。她指出:“它们的皮毛几乎完全防水,并能阻挡许多寄生虫。树懒身上的寄生虫要比体型相似的哺乳动物少。”

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

树獭已经丧失了哺乳动物的一些特征,其中之一就是哺乳树懒为后代所产乳汁的数量。

“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.

克利夫说:“树懒妈妈不会储存大量的乳汁,所以乳汁是一滴一滴地滴出来。”幼崽要紧贴着乳头,然后在乳汁滴出来时吸食。

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.

克利夫多年来一直在哥斯达黎加丛林中观察树懒,她对树懒的行为有深入的了解。“他们不跳也不跑。但它们拥有强壮的手臂。如果人类和树懒来一场手臂比拼,树懒绝对会赢。但是树懒不需要高速度的奔跑,甚至不需要支撑全身的重量,它们的腿却没有相同肌肉的质量。”

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,克利夫说,树懒这种“按兵不动”的生活态度不应该被误认为是懒惰。“他们不懒惰。生活在森林里的吼猴每天要睡18个小时,而树懒只睡10个小时左右。”

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.

如果树懒没有最终生活在被森林覆盖炎热潮湿的环境中,它们可能会活泼一些,运动节奏也快一些。但是经过无数世代进化,它们已经达到了完全适合所处环境的生活节奏。

“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.”

克利夫说:“这表明,它们不必跑来跑去地寻找食物。它们放松了整个系统。”

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