Small mammals – AEAS精读 (Y10-12)

The canopy, the upper level of the trees in the rain forest, holds a plethora of climbing mammals of moderately large size, which may include monkeys, cats, civets, and porcupines. Smaller species, including such rodents as mice and small squirrels, are not as prevalent overall in high tropical canopies as they are in most habitats globally.

Small mammals, being warm blooded, suffer hardship in the exposed and turbulent environment of the uppermost trees. Because a small body has more surface area per unit of weight than a large one of similar shape, it gains or loses heat more swiftly. Thus, in the trees, where shelter from heat and cold may be scarce and conditions may fluctuate, a small mammal may have trouble maintaining its body temperature.

Small size makes it easy to scramble among twigs and branches in the canopy for insects, flowers, or fruit, but small mammals are surpassed, in the competition for food, by large ones that have their own tactics for browsing among food-rich twigs. The weight of a gibbon (a small ape) hanging below a branch arches the terminal leaves down so that fruit-bearing foliage drops toward the gibbon’s face. Walking or leaping species of a similar or even larger size access the outer twigs either by snapping off and retrieving the whole branch or by clutching stiff branches with the feet or tail and plucking food with their hands.

Small climbing animals may reach twigs readily, but it is harder for them than for large climbing animals to cross the wide gaps from on tree crown to the next that typify the high canopy. A macaque or gibbon can hurl itself farther than a mouse can: it can achieve a running start, and it can more effectively use a branch as a springboard, even bouncing on a climb several times before jumping. The forward movement of a small animal is seriously reduced by the air friction against the relatively large surface area of its body. Finally, for the many small mammals that supplement their insect diet with fruits or seeds, an inability to span open gaps between tree crowns may be problematic, since trees that yield these foods can be sparse.

译文:

树冠是雨林中树木的上层,拥有大量中等大小的攀爬哺乳动物,其中可能包括猴子,猫,果子狸和豪猪。较小的物种,包括小鼠和小松鼠等啮齿动物,在高热带檐篷中并不像全球大多数栖息地那样普遍。
   温暖的小型哺乳动物在最上层树木的暴露和湍流环境中遭受苦难。因为小体积每单位重量的表面积大于相似形状的大表面积,所以它更快地获得或失去热量。因此,在树木中,可能缺乏热和冷的避风港并且条件可能波动,小型哺乳动物可能难以维持其体温。
   体积小,可以很容易地在树冠上的树枝和树枝中争夺昆虫,花朵或水果,但在竞争食物的过程中,小型哺乳动物被超越,食物丰富的树枝中有自己的策略。悬挂在树枝下方的长臂猿(小猿)的重量使得终端向下落下,使得带有果实的叶子落向长臂猿的脸部。步行或跳跃类似或甚至更大尺寸的物种可以通过折断和取回整个分枝或用脚或尾巴抓住僵硬的树枝并用手摘食物来进入外枝。
   小型攀爬动物可能很容易到达树枝,但它们比较大的攀爬动物更难以穿过树冠上的宽阔间隙,而不是典型的高树冠。猕猴或长臂猿可以比鼠标更远地投掷自己:它可以实现跑步开始,并且它可以更有效地使用分支作为跳板,甚至在跳跃之前跳过几次爬升。小型动物的向前运动通过与其身体的相对大的表面区域的空气摩擦而严重减少。最后,对于许多用水果或种子补充其昆虫食物的小型哺乳动物,无法跨越树冠之间的空隙可能是有问题的,因为产生这些食物的树木可能是稀疏的。