Primate Adaptations


Today we're going to be looking specifically at primates, not at behavioral theories or terminologies.

We have two goals:
Describe the physical characteristics of primates
Describe the general features of behavior and ecology

Question we're going to answer today:

What makes a primate?

How do we come up with a definition of the order primates? It is difficult because there's quite a range of differences in characteristics. For instance, there is a two-to-three-thousand-fold size difference between largest and smallest primates.

Primate Anatomy

A definition from 1873, written by St. George Mivart:
"Unguiculate, claviculate, placental mammals, with orbits encircled by bone; three kinds of teeth, at least at one time of life; brains always with a posterior lobe and calcarine fissure; the innermost digits of at least one pair of extremities opposable, hallux with a flat nail or none; a well-developed caecum; penis pendulous; testes scrotal; always two pectoral mammae."

A link to the Oxford English Dictionary (Available only to UM-affiliated users, sorry)

Seriously though, they're not very physically specialized. Not when compared to say a giraffe or a platypus! There are some defining characteristics, though.

Eyes: Primates are very visual. Compared to other mammals, the eyes have moved more to the forepart of the head. This gives good binocular vision.

Teeth: Incisors, canines, and molars. (The three kinds referred to in the definition.) Diversity of tooth types is because of diversity in diet. The canine teeth rip food and get it into mouth, while molars grind the food to prepare it for digestion. Felines, who have a less-varied diet, have less varied teeth.

Brain: A lot of development in the neo-cortex which implies heavier reliance on learning and memory. Also, olfactory bulb is rather reduced, especially in the ones with bigger neo-cortex. Older primates, like the prosimians, have a larger olfactory bulb but a smaller neo-cortex. More recent developments have a smaller olfactory bulb and larger neo-cortex.

Skeletal layout: Fairly generalized so it can be used for many different modes of locomotion. Skeletal proportions have great variation among species, mostly related to locomotion type.

Ecology and Behavior

Habitats

Worldwide geographic distribution: Primates are fairly widely distributed; on 5 out of the 7 continents (Not Australia or Antarctica.) They're more restricted now than before, mostly due to climate changes- they're basically a tropical order. Mostly they're found in the rain forests of SE Asia, west-central Africa, and South America. Exceptions: Barberry Macaque in N Africa, Japanese Macaque in Japan, and some mountainous types.

Habitat types: These differences in habitat are caused by differences in rainfall, going from highest to lowest.
Primary forest: Tall trees with a dense, multi-level canopy.
Secondary forest: Spots where primary forest has been disturbed so it doesn't have tallest trees- more dense understory due to more light getting in.
Gallery forest: Develops along waterways in drier areas.
Woodland: Trees are sparser and shorter, with more shrubbery.
Savannah: Made up of grass and scattered trees (pretty dry here).
Within any given habitat, there are microhabitats:

Microhabitats: These are smaller divisions within the same habitat: You might have altitudinal gradience where two species live in the same habitat but at different altitudes. Also, within a forest, they might use different levels of the canopy: Highest is the emergent trees (up to 300ft tall) that poke out above canopy. Next comes the main canopy, which has a lot more horizontal branches and vines and things. The main story comes next, with more trunks and vines, and finally we find the ground. Certain species may specialize in one particular height level, rarely venturing out of it. (This type of microhabitat is also known as vertical distribution)


Activity Patterns

Most mammals are nocturnal: they sleep during the day. Primates on the other hand are mostly diurnal. The holdouts are the prosimians (the less-developed primates who also have smaller neo-cortexes.) All apes are diurnal. All monkeys except the 'night monkey' are diurnal. Some monkeys could be called crepuscular maybe, but not nocturnal.


Locomotion

Primates, being 'unguiculate,' not only have nails or claws, but usually have flat nails instead of claws. This is because hands and feet have become modified for grasping.The exception is the prosimians; they still have nails.

The Classifications a.k.a Different ways to move:
Quadrapedalism; May be arboreal(african monkeys) or terrestrial (macaques and baboons). A specialized form called knucklewalking is seen in african apes, gorillas, chimps, and bonobos.

Leaping; Seen in squirrel monkeys. Vertical leaping from a clinging position on a trunk is seen in the prosimians such as the tarsiers and indries (who still have claws).

Suspensory climbing; Hanging down from hands from branches. Orangutans do this. Gibbons do a special type of suspensory travel; they brachiate.

Bipedalism: Examples are us; also chimps and spider monkeys do it. Mostly they bipdedal (if that's a word) for shorter distances or when carrying something, but don't use it as their primary mode of movement.

Diets

'...well-developed caecum...' This is a sac in the digestive system which comes off at the top of the large intestine but leads nowhere. Its harbors bacteria used in the digestion of some nutrients that we can't break down, such as cellulose or complex carbohydrates. Bacteria in the caecum digests this stuff for us.

Gross dietary categories
frugivore fruit-eater: orangutans
folivore leaf eater: leaf-eating monkeys
insectivore insect eater: tarsiers
gummivore gum eater (saps and gums from injuries to trees): tamarins and marmosets
omnivore animal & plant eater
faunivore animal eater (includes insectivores) but this category also includes invertebrate-eaters
herbivore plant eater (includes leaf and fruit eaters)

*Note if we say an animal is one of these types it doesn't mean that's all they eat! Some animals have stricter diets than others.


Spacing systems-- Nomadic-migratory vs. Philopatry

Many animals move around quite a bit. Primates don't move so much. They are called philopatric which means they stay in the same place. This is Ścause they live in such a complex environment; they need to know where to find food, sleeping areas, and predators. Therefore they stick around within an area that they know. Maybe an animal will move to another territory once when it reaches adulthood, but that's usually it.

Range terminology:
How far they go in one day; day range (often measured in length)
How far they go in a longer period of time (like a year); home range (area)
The area in home range which is used most; core area (area)
If they actively defend their home range, then it's called a territory and if they don't, then it's just called a home range.

Examples: Gibbons have territory and they defend it. They move pretty quickly, so their day rage is pretty long, but their territory is relatively small since they do defend it. The orangutan moves more slowly so its day range is shorter. Its home range, not being a territory, is pretty big, however. When undefended, home ranges often overlap quite a bit.


Social Groups: Solitary vs. Gregarious

Mostly, primates are social animals. Most mammals aren't. Holdouts, as usual, are the prosimians many of whom are solitary. Monkeys and apes are almost all in groups, the prototypical example being baboons who live in huge groups. An exception is the orangutan who is a solitary beast.

A Classification of Social Group Types
Note that these often correspond to mating system classifications.

Noyau: Animals have overlapping home ranges, and the sexes don't live together. There's no territoriality. Each female has a home range while males have larger home ranges that cover several female ranges. This is the system seen in orangutans. Usually goes with a promiscuous mating system.

Monogamy: One territory for each pair and their offspring. An example is the gibbons. Goes hand-in-hand with the monogamous mating system.

Polyandry: Each territory has one female and many males. Guess which mating system they use.

Multi-male group: (Should really be called multi-male, multi-female group, since each territory has many of both sexes.) Macaques are an example. Usually a promiscuous mating system.

One-male group: Such as the leaf-monkey. Usually a polygynous mating system. The leftover males form bachelor herds who raid periodically to take power and women from aging reigning males.

Fission-fusion society: This type is less common, but can be seen in chimps, bonobos, and spider monkeys. A group has shared territory. All the members are friendly to each other and work to keep non-group members out, but they don't travel toge ther as a group. They have smaller subgroups that join and split almost constantly.

Hamadryas baboons: This category is used almost just to describe their systems, so they got the naming of it. It is a complex hierarchical system, with several levels. The basic unit is a one-male unit, with accompanying females, but the units co mbine into larger groups called clans. These are made up of related males' groups who merge for a while to forage and socialize, but don't share women. Clans will sometimes merge to form troops who share common sleeping sites, often on cliffsides. Sometimes a troop will move as unit to a new location, but usually during the day they split into clans. A similar system is seen in the golden monkey and proboscis monkey, but it hasn't been so well described.