The colobines dominate the rainforests because their large many-chambered stomachs allow them to survive on leaves which are plentiful but difficult to digest. In less leafy habitats such as scrubland and more open habitats, the more versatile cercopithecines dominate. They include some of the most adaptable and intelligent of all non-hominoid primates . Some place these in a separate subfamily, the Cynopithecinae . Although the colobines are usually portrayed as leaf-eaters, it is more correct to describe them as specialising in less digestible food, of which leaves are a prominent example.
Leaves are the best year-round source of protein in the rain forest.
But leaves are hard to digest because of their high cellulose content and they are often laced with toxins. No other primates can survive on mainly leaves. Colobines have large complex stomachs containing cellulose-digesting bacteria . The bacteria not only helps to break down cellulose, but also deactivates the toxins that leaves are usually loaded with. Their stomachs have 3-4 compartments and many folds or pockets in the walls.