Why are blue whales so enormous? - Asha de Vos

為何藍鯨這麼大 - Asha de Vos

1,061,804 views ・ 2013-02-25

TED-Ed


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00:00
Transcriber: Andrea McDonough Reviewer: Bedirhan Cinar
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譯者: El Jj 審譯者: Jephian Lin
藍鯨是地球上有史以來
00:31
Blue whales are the largest animals that have ever roamed the planet.
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最大的動物。
00:34
They’re at least two times as big as the biggest dinosaurs—
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藍鯨的體型比最大的恐龍 至少大兩倍,
「真的很大!」
00:39
“that’s big!“—
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00:40
the length of a basketball court,
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身長等同一座籃球場,
00:41
and as heavy as 40 African elephants.
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且重量相當於四十隻非洲象。
00:44
If that’s not enough to make you marvel, here’s something that will.
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如果這還不夠讓你驚訝,
聽聽這個。
00:48
They’ve grown to this enormous size
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藍鯨可以只靠食用一種
00:50
by feeding exclusively on tiny shrimp-like creatures called krill—
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我們稱為磷蝦的蝦狀小生物 就長得如此巨大。
00:58
that are no bigger than your little finger.
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磷蝦的體型甚至不及你的小指頭呢。
01:00
In many ways, the sheer size of krill
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從很多方面來看,磷蝦的大小
01:02
seems to have driven the evolution of the blue whale.
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似乎促使了藍鯨演化成現在的樣貌。
01:08
See, krill are so small but are found in dense patches.
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磷蝦體型雖小
但大量成群出沒。
01:11
For increased efficiency,
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為了提升效率,
01:13
blue whales have evolved to use a feeding strategy called lunge feeding.
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藍鯨演化出一種
特殊的覓食策略
叫做「衝刺進食」。
01:17
Basically, the whale accelerates towards a prey patch
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基本上,藍鯨覓食時會加速游向獵物
01:20
and opens its mouth wide.
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並將嘴巴大大張開。
為了增加容量,它的嘴吧會不斷延展擴張。
01:23
To increase the capacity, its mouth expands.
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01:26
The special, accordion-like blubber layer
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從牠的鼻尖到肚臍
01:28
that extends from its snout to its belly button
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有一層類似手風琴的特殊結構
01:30
enables the whale to engulf large quantities of prey-laden water.
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使藍鯨可以大口吞入
富含獵物的海水。
01:42
With each giant gulp,
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這每一大口,
01:44
the whale takes in 125% of its body weight in water and krill.
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藍鯨都吞入相當於牠體重 1.25 倍的
海水和磷蝦。
01:50
The whale must then expel the water while retaining the yummy krill.
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接著牠必須排出吞入的海水,
並留住美味的磷蝦大餐。
01:54
To do this, it uses its baleen,
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此時,鯨鬚便派上用場,
01:56
the comb-like structure made of the same stuff our nails and hair are made of,
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鯨鬚是一種梳子狀的構造,
成分和我們的指甲及頭髮一樣,
02:00
and its tongue.
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牠的舌頭也同樣有所貢獻。
02:08
It’s pretty crazy that the blue whale’s heart is as big as a small car,
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藍鯨的心臟跟一台小型車一樣大
聽起來實在難以置信,
02:12
a child could crawl through its arteries,
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牠的動脈大得足以讓小孩在裡頭爬行,
02:15
its tongue weighs as much as an elephant,
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光是牠的舌頭,就跟一隻大象一樣重,
02:17
but its esophagus is so small,
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不過牠的食管,
卻小到難以吞嚥一條麵包。
02:20
the whale could choke on a loaf of bread.
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02:23
These whales are really not designed to feed on anything larger than krill.
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看起來,藍鯨還真的不適合
吃比磷蝦還大的食物。
02:31
It’s estimated that blue whales eat four tons of krill per day.
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根據估計,藍鯨一天可以吃下四噸的磷蝦。
02:35
Because of their incredible design,
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因為這種奧妙的構造,
藍鯨每一次進食
02:37
each dive provides the blue whale with 90 times as much energy as is used.
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所獲取的能量 為其所消耗的九十倍。
02:42
Every mouthful of krill provides almost 480,000 calories,
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每一口磷蝦,藍鯨都能從中攝取 四十八萬卡路里,
02:46
the same amount you get from eating 1,900 hamburgers.
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相當於 1900 個漢堡的熱量。
02:54
But, why are blue whales so big?
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不過,藍鯨究竟為何這麼巨大?
02:57
Blue whales are considerably larger than the largest living land animal,
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甚至連陸地上最大的動物──大象,
跟牠比起來都是小巫見大巫。
03:01
the elephant.
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03:02
The heavier an animal is,
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動物的重量
03:03
the greater its relative surface area.
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和其相對表面面積成正比。
03:06
As weight increases,
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當體重增加到了某個限度,
03:07
there’s a point at which the legs of that animal would simply collapse.
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動物就會因為腳承受不住重量
而摔倒在地。
03:12
That explains why elephants don’t stand on the delicate legs of a horse.
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這解釋了為什麼大象的四肢
不像馬那樣纖細精緻。
03:17
They need legs shaped like stout pedestals
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大象的腳必須像結實的圓柱,
03:19
to hold their bodies up against gravity.
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來支撐身體的重量。
03:25
In water, the situation is quite different.
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在水中,情況則大相逕庭。
03:28
Buoyancy counteracts the gravitational pull on the body
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浮力會抵消地心引力,
03:30
and their great bulk is therefore partially supported by the water.
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因此藍鯨龐大的身軀
有一部份是被水的浮力支撐住的。
03:34
So, the ocean is a great place for species that want to grow bigger.
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海洋可以說是提供了 想要長得大一點的動物
一個絕佳的環境。
03:39
The other secret to their size is their diet.
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飲食也在 龐大的身軀背後扮演重要的角色。
03:42
By evolving such a huge mouth,
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經演化而成的巨大嘴巴,
03:44
the whale’s have specialized to catch enormous quantities
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使藍鯨能夠輕易地捕獲
03:46
of highly abundant and nutritious prey,
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大量營養豐富的獵物,
03:49
which provides the energy needed to grow so big.
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提供其長到如此巨大所需的能量。
03:56
But, now maybe you’re wondering why blue whales aren’t any bigger?
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不過,你可能納悶
為何藍鯨沒有繼續無限制長大?
04:03
After all, the ocean sounds like nirvana for any growing beast.
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畢竟,乍聽之下,
海洋像是 這些龐然大物的樂土。
04:07
Well, while lunge feeding may have allowed blue whales
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這麼說好了, 雖然「衝刺進食」
04:09
to become the biggest animal to have ever roamed the planet,
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使藍鯨成為
地球上有史以來最大的動物,
04:12
by enabling them to feed efficiently in dense prey patches,
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但這樣高效率的進食模式
04:16
it isn't cost free.
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並非沒有代價。
04:18
Scientists compared all the costs involved with lunge feeding
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科學家將「衝刺進食」所需代價
04:21
to the energy gained from the krill they eat.
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與從磷蝦身上獲取的能量 做了比較。
04:23
What they found is that when the whale’s body increases in size,
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發現藍鯨隨著體型增長
04:27
the energy that body demands rises faster
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身體所需能量的成長速度
遠超過食物來源所能提供的量。
04:30
than the extra energy they get from their food.
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04:35
Feeding whales needs 15 times the energy required to remain still
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「衝刺進食」所需能量 是維持靜止時的十五倍,
04:39
and 5 times more energy than used when swimming.
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也是游泳時的五倍。
04:45
Calculations show that the largest a lunge feeder can grow is 33 meters,
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根據計算,使用「衝刺進食」的動物
最多可以長到三十三公尺長,
約略是藍鯨的大小。
04:51
pretty much blue whale size.
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04:53
Turns out blue whales have a lot to thank krill for:
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看起來藍鯨可是欠了磷蝦不少人情:
04:55
neat, evolutionary adaptations that would not have been possible
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若非磷蝦這麼小,
藍鯨不可能發展出 這麼細緻的、演化上的環境適應。
04:59
if krill were not so small.
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05:00
It’s incredible that these tiny creatures have allowed blue whales
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像磷蝦這麼小的生物
竟能使藍鯨挑戰 地球上生物體形的最大極限,
05:04
to really push the limits of size on our planet.
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確實令人嘖嘖稱奇。
05:07
Makes you wonder if that old adage, “you are what you eat,”
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不禁使人懷疑,
「人如其食」這句俗語
05:11
really does apply in blue whale world.
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似乎不適用在藍鯨身上。
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