Some mammals stayed small or evolved to occupy niches previously occupied by tiny to medium-sized animals.

一些哺乳动物保持小的体型，另外一些则开始进化取代了之前是小到中型动物的族群。

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Medium-sized mammals, such as beaver and snowshoe hares, can be an important secondary food source.

一些中等的哺乳动物，比如海狸以及北美野兔也是它们重要的第二食物来源。

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