Those that are small-to-medium sized also eat insects. Those that are medium-to-large sized also eat leaves. Kay"s threshold - 500 grams: insectivores tend to weigh less than this limit, no folivore is smaller than this weight (eg. howler monkey) must travel farther to find it (means longer daily path lengths) eating insects difficult to catch and they"re small! eating leaves (& shoots, buds) they"re a low-energy resource, so must eat a large amount www. notesolution. com. secondary compounds (tannins, alkaloids) which give stomach aches, weird stomach morphology. gut microorganisms digest leaves for primates (animals that eat fruit don"t have to worry about this) colobus, lepilemur, and macaca are leaf eaters. sharp, shearing crests (cutting a paper with scissors) scramble competition: when a resource is exploited by the individual which arrives and uses it first (eg. olw and grass, because grass is everywhere, very dispersed food situation.