Comparative Primatology

Primates:

Lemurs
a)  Lemurs live only on the island of Madagascar and the Comoro Islands.  They once were found in old and new world, but now are extinct everywhere but this old world location off the coast of Africa.  Madagascar has 2 seasons "a hot, rainy season from November to April; and a cooler, dry season from May to October."  (http://www.wildmadagascar.org/overview/loc/19-climate.html#sthash.OioEXvqV.dpuf) It is tropical, hot and humid, and subject to cyclones.  Due to the origins of the Island and it's location before the landmass broke up, it shares certain kinds of plant and animal life with south america but not with the African Continent.  One example is the traveler's tree (www.wildmadagacar.org).  Madagascar was once totally covered with trees but is subject to deforestation for plots to grow rice on.  The trees are an important part of the Lemur's living environment since they are largely arboreal. 
b) True Lemurs are the size of a small to large house cat (http://anthro.palomar.edu/primate/prim_2.htm). Dwarf and Mouse Lemurs are the size of mice (like normal house mice, not the NYC subway dwelling rat.  That would be more like a true lemur).  The Indriidae are larger, some can measure nearly 4 feet from head to toe and can weigh around 20 pounds. Aye Aye's are smaller and less readily observed due to their nocturnal nature, as well as being relatively quiet and solitary. 
In terms of sexual dimorphism, females tend to dominate the males and tend to be the ones who take care of defending the group.  Females can also be quite aggressive towards others of lower social rank.  Males of higher rank tend to 'swagger' while lower ranked males tend to cower.  Their physical differences tend more to differences in color (for instance, in the ring tailed lemur, only males are all black), rather than substantial differences in size. 
c) The diversity of lemur species on the island of Madagascar has to do with the size and variation of the island, as well as it's isolation from the continent of Africa.  There are a wide number of Lemurs of different size. mostly arboreal some terrestrial, and mostly diurnal instead of nocturnal.  The little spur in the stink gland of the ring tailed lemur that helps them slash the bark of trees as well as the stink glands that they even use in battle (rubbing on their tails and then waving their tails around until the other guy gives up and leaves)... are examples of adaptation to the environment (the spur being a very arboreally handy trait).  
d)

Spider Monkey

a)Spider Monkeys are native to Central and northern South America, reaching as far north as the southern area of Mexico.  "The habitation of Spider monkeys primarily consists of the evergreen rainforests, semi deciduous and mangrove forests." http://www.angrydmonkey.com/guide-habitat-distribution.html  They live in trees (arboreal) and are awake during the day (diurnal). 

\b) Spider Monkeys can be fairly large growing up to 2 feet in size (http://www.srl.caltech.edu/personnel/krubal/rainforest/Edit560s6/www/animals/spidermonkeypage.html).  They have long arms and legs and a prehensile tail. They live in the upper layer of the trees and tend to find their food among the treetops.  They have hands like hooks and are acrobatic movers, some strides covering up to 40 feet (http://www.angrydmonkey.com/a-look-at-the-physical-characteristics.html).  There is not a great deal of sexual dimorphism (http://pin.primate.wisc.edu/factsheets/entry/black_spider_monkey), but they tend towards the same relative coloring and very similar sizes as well.  

c) Spider monkeys lack a thumb, but have a very long prehensile tail that they use for balance when walking on the ground as well as for stability when climbing and brachiating among the trees.  This lack of a thumb would seem to put them at a disadvantage, and yet these hook like hands make them excellent swingers and capable of swinging across great distances. 

this lack of a thumb would be an excellent adaptation for being able to stay in the top part of the trees, as would their extra long tails. 

d)

Baboon

a)Baboons are found in equatorial Africa in a more arid environment close to the savannah.  They live partly on the ground and partly in the trees, spending a more significant amount of their hunting time on the ground. 

They also lack a prehensile tail which definitely influences their interaction with their environment as well as choosing to spend most of their time on the ground. 

b)Baboons are 20-34 inches in height and their weight can vary widely from 30 to over 80 pounds.  One factor is the very obvious sexually dimorphic characteristics.  There are size as well as fur differences between the sexes in baboons.  In some baboons even the bones of their face are different (http://www.ncbi.nlm.nih.gov/pubmed/2021194).  Males are noticably larger, and if the species is colorful, the male is more colorful, more fluffy and more showy to gain the attention and sexual selection of the female. 

c) Their non-prehensile tail as well as physical strength and quadrapedal stride have definitely adapted to a mostly terrestrial lifestyle. 

Gibbon: 

a)Gibbons live in Forrest areas of southern Asia.  They are arboreal and, just the opposite of the aforementioned baboon, they rarely touch down from the trees.  Gibbons brachiate and can move through the forest as fast as 35 miles per hour (http://animals.nationalgeographic.com/animals/mammals/gibbon/?source=A-to-Z) and can bridge gaps as wide as 50 feet.  

When the Gibbon decends to the ground, they walk on two feet with their arms up for balance.  They are the most bipedal of the non-human primates (http://animals.nationalgeographic.com/animals/mammals/gibbon/?source=A-to-Z).  

b) They are sexually dimorphic, can vary somewhat in size and somewhat in coloring.  They are also said to be monogamous which is not a common primate trait (http://animals.nationalgeographic.com/animals/mammals/gibbon/?source=A-to-Z).  They seem to vary in color from male to female, as well.  

As with other primate species, their hooked hands and long arms make them excellent climbers and swingers, and are excellently adapted for living an arboreal life.  Their swinging capability also makes them able to travel safetly without leaving the trees to find food, keeping a relative distance from preditors that may be on the ground. 

Chimpanzee

Chimpanzee live in sub-Saharan Africa in the rain forests, woodlands, and grasslands.  They are well adapted to terrestrial or arboreal living, and can climb well. They are adapted to a wide variety of climates.  They are part of the ape class and do not, therefore have a prehensile tail. They have a generalized diet that includes seeds, fruit, plants, insects and sometimes meat.  The grow to 4 to 5.5 feet tall and 70 to 130 pounds in weight.  Males are generally larger than females, females have more obvious mammary tissue (specifically after having young).  Besides differences that are similar to human sexual differences, the differences between males and females are not too big.  

Their anatomy tends toward the fairly generalized which helps them to adapt to such varying areas and climates.  

Summary:
It does seem that environment does play a significant factor in the formation of some aspects of the primate physiology (such as arm length, hand shape, tail, etc... those with prehensile tails seem more likely to be arboreal whereas those without tend to be more terrestrial). In other senses, such as size there is somewhat of an effect (larger animals tend to be on the ground, smaller tend to be higher in the trees, though not exclusively), and sexual dimorphism tend to be less dramatically influenced by their need to adapt to their habitat.  There is not really an explaination in the habitat for the differences in the physical display among baboons, yet sexual selection and genetic heredity of desireable traits do seem to be excellent explainations for such things.  It also seems there is a wide variety among primates as to whether they are almost the same or very different between the genders within their own species.  This seems more of a speciated adaptation than one related to climate or living conditions.