The bug-eaters: Insectivores
Insectivores eat a diet heavy in insects; this is where the primates began: as small early mammals eating small insects. Today, many primates eat a few insects — like the chimpanzees who fish termites out of their mounds by using twigs — but few focus their diet on insects, and even those who do still eat other foods such as tree gum and leaves. But for mouse lemurs and some other prosimians, insects may compose close to half the diet. The characteristics of these insectivores include
Generally very small size, normally under 100 grams (¼ pound)
A nocturnal lifestyle
Sharp teeth for processing insect bodies
An arboreal lifestyle
A short and simple digestive tract
The insectivorous primates include the African bush baby or galago, a prosimian that also eats tree gum. It has enormous ears and, unlike most primates, uses these rather than vision to locate its food sources. Weighing up to 5 kilograms (about 10 pounds), the bush baby can leap as far as 4 meters (12 feet) at a time.
The leaf-eaters: Folivores
Folivorous primates focus on eating leaves but still get plenty of variety in most of their diets — they also eat fruit and seeds if they’re available. The red howler monkey of South America dines on nearly 200 different species of plants and apparently prefers eating younger rather than more mature leaves. The most folivorous primates are characterized by the following traits:
Generally medium size (or large, compared to insectivores), averaging 5 kilograms (10 pounds)
A nocturnal lifestyle
Mixed sharp and flat teeth for processing vegetation (snipping it with the incisors, shearing it with the premolars, and then crushing it with the molars)
A long and complex digestive tract used to process vegetation
Leaves are hard to digest, so folivores’ guts are larger and more complex than those of many other primates; essentially, leaves ferment in primate stomachs. And because leaves don’t have a very high caloric content (relative to a lot of other potential foods), folivores eat a lot of them. (It takes a lot of leaves to make up a pound, which is about what some captive lemurs eat each day.) How the food is dispersed in the trees, what season it is, and how the animals get around are all linked in complex ways.
The fruit-eaters: Frugivores
The frugivores (fruit-eaters) focus on fruit, but they eat other things as well. Among the most frugivorous primates are the apes, and of these, the most fruit-obsessed are the orangutans, which devour large quantities of the custard-like durian fruit as well as the leaves, fruit, and seeds of nearly 400 other plant species. The frugivores have a sweet tooth, focusing on sugary plant products, and they display the following characteristics:
Generally large size (compared to most primates), averaging over 10 kilograms (20 pounds)
A diurnal lifestyle, being active mainly at day
Mixed sharp and flat teeth for processing vegetation (but sometimes with particularly large incisors for opening up tough-skinned fruit)
Of the more striking characteristics of the frugivores is their good memory. They’re very good about remembering just where good patches of fruit appear each year and therefore spend a little less time foraging in search of food than some other primates. This skill can have important (if currently unknown) effects on variables like the complexity of social interactions because they spend more time sitting, grooming, and feeding together than traveling in search of food.
Monkeying Around: Primate Locomotion
How primates locomote — get from place to place — is fascinating, and it can tell you a lot about how they live. Some leap from limb to limb, others swing like trapeze artists, and of course humans walk on two feet (unless you’re a pirate or something). I discuss the main types of locomotion in the following sections; they’re illustrated in Figure 4-5.
Illustration courtesy of Cameron M. Smith, PhD
FIGURE 4-5: The main types of locomotion.
Stand back, Tarzan: The brachiators
Brachiation is swinging from one hold (like a tree limb) to another, and the speed champion species here is the gibbon. Southeast Asian gibbons can swing through forest canopy at more than 30 miles per hour, about ten times as fast as most humans walk. Slower brachiators are the big, heavy orangutans, who hang, reach, and shift their body weight instead of really smoking through the canopy like the gibbons. Brachiators have several main anatomical characteristics:
Long arms: The longer the muscle, the greater its power, so evolution has selected for longer and more powerful arms over time.
Short, relatively weak legs: These animals don’t spend much time on the ground and really prefer to hang from their hands.
Very powerful hands: These primates have strong, long fingers but very small thumbs; thumbs would get in the way of the hooking action used to grasp tree limbs and vines.
Bug-bashers: The vertical-clingers-and-leapers
The vertical-clingers-and-leapers (VCLs) do just that: They hug tight to a tree trunk, with their spine vertical, until they’re ready to move, and then they twist at the waist and push off hard with their legs, leaping at their target. That target is often an insect, a juicy treat that makes up a large part of their diet. The VCLs include the tarsiers and the lemurs, both members of the prosimian group discussed earlier in the chapter. Their anatomical characteristics include
Short,
