Chapter six: primate ecology

Chapter Review

diet and feeding behavior

Diet, in primates as well as in all other animals, plays an important role in determining the total amount of energy available to an individual animal. Dietary efficiency intake can be analyzed in terms of metabolic intake, which in turn can be examined in terms of four categories of metabolic requirements:

Basal metabolic rate (BMR), which is the resting expenditure of an organism.

Larger organisms, while requiring higher absolute metabolic costs, actually require less on a relative scale (that is, metabolic cost per unit mass).

Metabolic expenditure incurred by activity level.

This is energy required to sustain activities that go beyond simply existing.
Average expenditure amounts to approximately twice the BMR.

Growth and development.

Particularly when examining infants and juveniles, energy intake and expenditure are higher than expected from body size and activity; much of the energy is used for organ and skeletal development.

Costs of reproduction for females.

Pregnancy can require up to a 25% increase in caloric intake.
Lactation is particularly expensive, requiring up to a 50% increase in caloric intake.

Primates are able to exploit a wide range of food sources, which include insects, animals, fruits, seeds, mature leaves, shoots/immature leaves, underground roots, piths, and exudates (Fig. 6.1). From these sources, they are able to extract the basic elements—carbohydrates, fats, proteins, vitamins, and minerals—to sustain their bodies. However, some of these food sources—particularly mature leaves and unripe fruits—include a battery of secondary compounds (such as alkaloids, tannins, and lignin), which make them less palatable to all but those species specialized at neutralizing their harsh digestive effects.

6-1

Figure 6.1 Female baboon feeding.
Image credit: Joan Silk.

In fact, even if folivorous primates (leaf eaters) could neutralize the host of secondary compounds ingested with a meal of mature leaves or tubers, they would still have difficulty procuring enough nutrition from those materials by the action of stomach acids alone. So these primates possess certain intestinal bacteria that are able to break down the tough cellulose, allowing them to obtain adequate nutrition. For this reason, folivorous primates tend to have more capacious guts (either hindgut or foregut) than primates that habitually consume more fruits and/or fauna. Large guts are necessary in many respects, not the least of which include the following:

Increasing the total amount of food that can be consumed at one session.
Allowing enough time for bacteria to break down secondary compounds and cellulose.

Because gut size is an important component in the efficient digestion of foliage, folivorous primates tend to have larger total body size as well. Several species of primates have separately evolved specialized gastrointestinal tract dimensions to help them digest food efficiently.
Primates that emphasize the intake of ripe fruits and/or insects generally deal with lower degrees of digestive combativeness in their diet and have simpler stomachs. Primarily insectivorous species tend to have the simplest digestive systems, whereas frugivorous primates are more variable (some also include relatively high quantities of leaves in their diets). While the following lists does not do justice to the diversity of primate diets, these mechanical attributes relating diet, behavior, and gut morphology attempt to address some of the challenges faced by fruit-eating and leaf-eating species.

Fruit-Based Diet

Fruits are a high-quality food item but tend to be patchily distributed.
A diet consisting primarily of fruit requires larger ranges and, therefore, increased metabolic requirements.
Ripe fruit tends to have a high degree of readily digestible parts, which do not require much digestive processing.
Adequate nutrition depends largely on the amount of food successfully procured rather than the effectiveness of digestion.
A premium is placed in faster gut passage, which is facilitated by shorter guts.

Leaf-Based Diet

Leaves are a lower-quality food item, which tend to be ubiquitously distributed.
Specialized leaf-eaters tend to have smaller ranges and, therefore, expend less energy during the course of a day.
Leaves require a high-degree of processing in the digestive system.
Adequate nutrition is most limited by how effectively nutrients are extracted from the food source rather than the amount that is successfully procured.
A premium is placed on effective digestion, which is assisted by larger guts.

These different feeding strategies have potentially profound implications for the evolution of primate cognitive abilities. Interaction at many levels suggests that diet and feeding ecology may have influenced the evolution of primate intelligence, which is discussed in greater detail in Chapter 9.

Dietary Ecology and Aspects of Sociality

The connection between feeding behavior and home range alluded to earlier is one of the reasons primates may have to defend their territories. That is, when resources are limited or concentrated in small areas, resource-defense territoriality can occur. Some primates defend their food resources against outside groups, whether they are of the same species as themselves or not. Not all primate species are territorial, however. Those that do not actively defend their resources often have prolonged contact with other populations and species while feeding.
However, resource defense is not the only reason for primate groups to want to keep to themselves. Mate defense, occurring in species such as gorillas, red colobus monkeys, langurs, and others, is characterized by often violent intergroup encounters between males. Primates may also defend themselves against predators, either through alarm calls, fleeing, or direct confrontation.

Moreover, basic group composition among primates may be influenced by feeding and competitive strategies for access to resources. Resource competition may also generate hierarchical relationships in some primate species.

Back to Top