Primate Traits

1. Primate Environments

1a. Lemurs—formerly occupying other tropical regions on the earth, these primates have been confined to only the island of Madagascar and nearby Comoro Islands. Lemurs live in forests on Madagascar ranging from rainforest type regions to dry deciduous forests.

1b. Spider monkeys—these are arboreal primates that thrive in the upper canopy, which allows them isolation from competition. Sometimes they occupy deciduous and mangrove forests.

1c. Baboon—Baboons are highly adaptable primates capable of living in a wide variety of environments including savannahs, open grasslands, evergreen forests, and gallery forests.

1d. Gibbon—these primates live in tropical hill forests, often found about 1000 ft. They are also found to inhabit lowland forests, selectively logged primary freshwater swamp forests, selectively logged lowland forests, selectively logged hill forests, and submontane forests.

1e. Chimpanzee—Chimps are another highly adaptable primate and live in a wide variety of environments. Their habitats include dry savannahs, evergreen rainforests, montane forests, swamp forests, and dry-woodland savannah mosaics. 

2. Body Size and Sexual Dimorphism

            2a. Lemurs—There is some sexual dichromatism between some male and female lemurs. For the most part, there is not really any distinguishable size difference between the sexes.

            2b. Spider monkeys—As with lemurs, there is not much distinguishable dimorphism here. However, female spider monkeys do have a very slightly lower average size than males; aside from this, they are mostly similar.

            2c. Baboon—These primates show distinct sexual dimorphism. Males can often be up to two times as large as females, and there are distinct facial features—in dental structure, especially relating to the canines, as well as skull size.

            2d. Gibbon—Dimorphism for gibbons is less distinct, but existent. There are slight size differences, with males being slightly larger than females, but there are fur color differences in many species between the sexes.

            2e. Chimpanzee—Chimpanzees exhibit an average amount of dimorphism, with fully-grown females being about 25% smaller and about 15-20% shorter than fully-grown males.

3. Body Size and Sexual Dimorphism as an Environmental Adaptation

            3a. Lemurs—Given such a restricted environmental diversity, it is not surprising to see limited sexual dimorphism here. The dimorphism present in the fur colors could be related to sexual attraction, with more colored lemurs being more attractive. It could also serve as a sort of camouflage in different environments since lemurs are so small and vulnerable to predation.

            3b. Spider monkeys—Again we can see that restricted environment diversity is also paired with limited sexual dimorphism. The slight size differences between males and females could be from a slight difference in daily activities (if males hunt/gather more) or, again, sexual attraction (females being attracted to bigger males/males being attracted to smaller females).

            3c. Baboon—The sexual dimorphism is very prominent. With males being so much larger on average, as well as having distinct coloration, these could definitely be tied to sexual attraction. I would hypothesize, however, that given that their environments are less in the trees and more on the ground, there is little that these primates can do to escape each other if challenged. The more prominent canines in males could also be adapted to exude dominance. If one were to examine social behaviors and find that baboons are known to fight with each other over mates, food, living areas, etc., then these differences in size and color could be adapted by males bearing these traits (larger, more colorful, bigger teeth) winning challenges more often.

            3d. Gibbon—These only have slight expressions of dimorphism, though more than lemurs and spider monkeys, and their environments are also more varied. However, even though gibbons do live across more of the environmental spectrum, they are arboreal. Fur differences have been linked to sexual readiness or adequacy, and size may be linked to males needing to hunt/gather more than females.

            3e. Chimpanzee—Since chimps live across a wider variety of environments than gibbons, it is once again not very surprising to find a higher exhibition of sexual dimorphism. Males are distinctly larger and taller than females, though there are no notable differences in color. This size difference can be adapted to males hunting/gathering more than females, who would have to care for their young since they are placental mammals and bear their offspring before birth, essentially being hindered to compete for food.

4. In summary, I found that, in general, the more varied these primate’s environmental habitats were the more sexual dimorphism would be present in current species. This is a generalization, of course, because we see that baboons have what seems to be an extreme case of dimorphism. Regardless of how their traits adapted in the first place, they are present today and can be noted as clear evidence of an environment having a diverse effect even within a single species. Environmental effects do not have to be limited to sexual dimorphism, though. Spider monkeys, being arboreal, have tails that have adapted to function somewhat like a fifth hand or limb, with a furless tip that can hold on to and grip tree branches.

Lemurs

Spider Monkeys

 Baboons

Gibbons

Chimpanzees