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Why are whales so big? One answer is simply that they can be.
為什么鯨魚的體型如此龐大？有一個答案很簡單，它們就是能長到這么大。
The size of land animals is constrained in part by their need to support themselves against the force of gravity.
陸地動物體型受限的部分原因是因為它們需要依靠自身對抗地心引力。
Marine creatures have that support provided free, by the medium they live in.
海洋生物可以通過它們生活的環境為媒介免費獲得這種支持。
Even so, what is possible is not always sensible. Resources put into growth are unavailable for reproduction.
即便如此，可能的事情并不總是明智的。投入生長的資源無法再生產。
Given that whales can and do become big, however, a second question arises: what, if anything, stops them being even bigger?
鑒于鯨魚可以且確實龐大，第二個問題就來了：如果有的話，有什么可以阻止它們變得更大？
Jeremy Goldbogen of Stanford University and his colleagues suspect that the answers to both questions are related to the animals' food supply.
斯坦福大學的Jeremy Goldbogen和他的同事懷疑兩個問題的答案和動物的食物供應有關。
And, as they describe in a paper in Science, they have gathered data that illuminate how this might work.
正如他們在《Science》雜志中發表的一篇論文所述，他們收集了數據，闡明了可能的運作方式。
Broadly, big whales come in two varieties. Toothed whales, such as sperm whales, hunt individual prey.
總的來說，大鯨魚有兩種。齒鯨，如抹香鯨，捕食單個獵物。
Baleen whales suck in mouthfuls of water and extract small organisms such as krill, using fibrous buccal filters.
須鯨，用纖維狀的口腔過濾器吸入大量的水，并從磷蝦等小生物中吸取營養。
The biggest whales of all (blue, humpback and so on) are baleen whales.
所有鯨魚中最大的鯨類（藍鯨、座頭鯨等）是須鯨。
This might be viewed as paradoxical, because on land, as predators get bigger, so do their individual prey.
這或許被認為是很矛盾的，因為在陸地上，捕食者越大，它們的獵物也越大。
Both toothed and baleen whales often hunt by diving deep—prey being more abundant at depth.
齒鯨和須鯨通常都潛入深海捕食，因為深海里的獵物更多。
To do this they have to hold their breath, which limits how long they can stay underwater.
為了去深海捕食，它們會屏住呼吸，這就限制了它們在深水中停留的時間。
One explanation of giantism in whales is that because bigger whales can hold their breath longer, they can spend more time hunting.
鯨魚巨大體型的解釋之一是因為體型越大，屏息時間越長，這樣它們就能花更長時間在深海捕食。
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