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树懒为什么这么慢? —肯尼·库根

Why are sloths so slow? - Kenny Coogan

1796年 托马斯·杰弗逊收到了一箱他无法辨认的骨骼
In 1796, Thomas Jefferson received a box of bones he couldn’t identify.
长而尖利的爪子让他想到了狮子
A long, sharp claw reminded him of a lion,
但臂骨却暗示这是一种更大型的动物
but the arm bones suggested a larger animal,
大概有三米长
one about three meters long.
想到这可能是巨大的北美狮未知物种
Thinking it might be huge unknown species of North American lion,
杰弗逊警告探险者刘易斯和克拉克
Jefferson warned explorers Lewis and Clark
要留心这种神秘的食肉动物
to keep an eye out for this mysterious predator.
但杰弗逊的这一箱骨骼并不是来自一头狮子
But Jefferson’s box of bones didn’t come from a lion.
他们来自一种已灭绝的巨型树懒
They came from an extinct giant sloth.
史前地懒在大约3500万年前首次出现
Prehistoric ground sloths first appeared around 35 million years ago.
几十种物种居住在北美、中美和南美
Dozens of species lived across North, Central and South America,
还有其他古代生物 比如乳齿象
alongside other ancient creatures like mastodons
和巨型犰狳
and giant armadillos.
一些地懒是像猫一样大小的 比如巨爪地懒科
Some ground sloths, like the megalonychid, were cat-sized,
但是许多地懒体型巨大
but many were massive.
杰弗逊的地懒 杰氏巨爪地懒 有大概一吨重
Jefferson’s sloth, Megalonyx, weighed about a ton,
和大地懒属比起来 这已经算小的了
and that was small compared to megatherium,
大地懒属可重达6公吨 和一只大象一样重
which could reach six metric tons, as much as an elephant.
它们在森林和热带稀树草原中漫步 利用它们强壮的手臂和尖利的爪子
They ambled through the forests and savannas using their strong arms and sharp claws
拔起植物、爬树
to uproot plants and climb trees,
啃食草、叶子和史前鳄梨
grazing on grasses, leaves, and prehistoric avocados.
事实上 如果没有巨型树懒 我们如今可能就不会有鳄梨了
In fact, we might not have avocados today if not for the giant sloths.
稍小些的动物无法吞下鳄梨巨大的种子
Smaller animals couldn’t swallow the avocado’s huge seed,
但树懒们可以
but the sloths could,
并且是它们让鳄梨树得以四处蔓延
and they spread avocado trees far and wide.
地懒繁荣了几百万年
Ground sloths flourished for millions of years,
但大概10000年前 它们开始消失
but around 10,000 years ago, they started disappearing
和西半球的其它巨型哺乳动物一起
along with the Western Hemisphere’s other giant mammals.
研究者们认为地懒可能是被迫离开家园
Researchers think that ground sloths could have been pushed out
由于即将到来的冰川纪
by an oncoming ice age,
或者和其它物种的竞争 也许是人类
or competition with other species, maybe humans,
人类在大多数树懒灭绝的时期来到了这块区域
who arrived in the region around the time most of the sloths went extinct.
一些小一点的树懒存活下来了 并且迁移到树顶上
Some of the smaller sloths did survive and migrated to the treetops.
如今 还有六种物种居住在雨林的树冠上
Today, there are six species left living in the rainforest canopies
在中美和南美
of Central and South America.
在树上活动是躲避天敌的好办法
Hanging out in the trees is a good way to avoid predators,
并且会有足够的叶子供食用
and there are plenty of leaves to eat.
但是这种饮食是有缺陷的
But this diet has its drawbacks.
动物从食物中获取能量 并且使用能量四处行动
Animals extract energy from food and use that energy to move around,
保持它们的体温
maintain their body temperature,
保证他们器官的运转
keep their organs working,
还保证了其它生存所需的活动
and all the other activities necessary for survival.
但树叶并没有很多能量
But leaves don’t contain much energy,
而且他们仅含的能量也很难利用
and that which they do have is tough to extract.
大部分食草动物在叶类食物外 辅以含有更高能量的食物
Most herbivores supplement a leafy diet with higher energy foods
比如水果和种子
like fruit and seeds.
但树懒 特别是三趾树懒 几乎仅仅依靠树叶存活
But sloths, especially three-toed sloths, rely on leaves almost exclusively.
它们在进化中已经形成了应对这种限制性膳食的极佳策略
They’ve evolved finely tuned strategies for coping with this restricted diet.
首先 它们尽可能多地汲取食物里的能量
First, they extract as much energy from their food as possible.
树懒拥有占据身体三分之一的多腔胃
Sloths have a multi-chambered stomach that takes up a third of their body,
不同种族略有不同
and depending on the species,
它们可以花五到七天 甚至几周时间 消化一餐饭
they can spend five to seven days, or even weeks, processing a meal.
这个问题的另一半答案 就是使用尽可能少的能量
The other piece of the puzzle is to use as little energy as possible.
树懒们这么做的一种办法 当然就是 几乎不怎么行动
One way sloths do this is, of course, by not moving very much.
它们大部分时间都用来吃东西、休息或睡觉
They spend most of their time eating, resting, or sleeping.
它们一周从树上下来一次上个厕所
They descend from the canopy just once a week for a bathroom break.
当树懒行动的时候 速度也不会很快
When sloths do move, it’s not very fast.
穿过附近一般大小的街道要花树懒大概五分钟
It would take a sloth about five minutes to cross an average neighborhood street.
这种不紧不慢的生活方式说明树懒并不需要很多肌肉
This unhurried approach to life means that sloths don’t need very much muscle.
事实上 它们比其它相似大小的动物少了30%肌肉
In fact, they have about 30% less muscle mass than other animals their size.
树懒保持体温也仅需要比较少能量
Sloths also use less energy to keep themselves warm
因为它们的体温可以上下浮动5摄氏度
because their body temperature can fluctuate by about five degrees Celsius,
这种体温跨度比冷血爬行动物要小 不过比大部分哺乳动物都大了
less than a cold-blooded reptile, but more than most mammals.
这些体质和行为的适应使树懒的能量消耗和新陈代谢率
These physical and behavioral adaptations minimize the sloth’s energy expenditure,
降到最低
or metabolic rate.
三趾树懒在所有哺乳动物中新陈代谢最慢
Three-toed sloths have the slowest metabolism of any mammal.
巨型大熊猫是第二慢的
The giant panda is second slowest,
二趾树懒排名第三
and two-toed sloths come in third.
行动缓慢使得树懒可以在它们的树顶栖息地茁壮成长
Moving slowly has allowed sloths to thrive in their treetop habitat.
但这也使得树懒成为其它生物栖息环境的良好组成部分
But it’s also made the sloths themselves a great habitat for other organisms,
包括藻类 它们提供了额外的掩护 可能甚至还会成为一顿点心
including algae, which provides a little extra camouflage, and maybe even a snack.
树懒可能不会再有巨型的了
Sloths may not be giant anymore,
但是这并不影响他们被人们记住
but that doesn’t make them any less remarkable.

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视频概述

树懒被人们记住,大概就是因为它们的慢,那这里就来解释解释为什么他们会行动如此缓慢

听录译者

收集自网络

翻译译者

可可天使

审核员

与光同尘

视频来源

https://www.youtube.com/watch?v=-64U7WoBrqM

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