The canopy, the upper level of the trees in the rain forest, holds too much of climbing mammals   of moderately large size, which may include monkeys, cats, civets, and porcupines. Smaller species, including such as nice and small squirrels, are not as common overall in high tropical canopies as they are in most habitats globally. Small mammals, being warm blooded, suffer hardship in the exposed and uncertain 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 rapidly. Thus, in the trees, where protection from heat and cold may be scarce and conditions may be changeable, 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 defeated, in the competition for food, by large ones that have their own strategies for browsing among tbod-rich twigs. The weight of an ape hanging below a branch draws the leaves down so that fruit-bearing leaves drop toward the ape's face. Walking or leaping species of a similar or even larger size access the outer twigs either by breaking and gaining the whole branch or by catching hold of hard branches with the feet or tail and picking 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 one tree top to the next that typify the high canopy. A 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  . The forward movement of a small animal is seriously reduced by the air friction   against the  ly large surface area of its body. Which of the following questions does the passage answer?
How is the rain forest different from other habitats? How does an animal's body size influence an animal's need for food? Why does rain forest provide an unusual variety of food for animals? Why do large animals tend to dominate the upper canopy of the rain forest?