Apes are distinct from other primates such as monkeys for the one main reason that apes do not have tails. There are 16 species of ape alive today split into two families: hominidae (great apes) and hylobatidae (lesser apes). The great apes include humans, chimps, gorillas and orangutans, while the lesser apes are gibbons and siamangs. The two families are closely related scientifically and share several common traits, but also have marked differences.
The most obvious difference between greater and lesser apes is general size. The smallest great apes are the bonobo chimps which grow to between 3 and 4 feet in height and weigh between 59 to 134 pounds. In comparison, the siamang, which is the largest lesser ape, grows to between 2 and 3 feet in height and weighs 22 to 26 pounds. All lesser apes have very long thin arms in comparison to leg length, while in great apes this is less pronounced. In species such as humans and gorillas the arm to leg length difference is more even. The great apes also tend to have larger brain cases and more prominent facial features.
In relation to natural home range, for the most part, greater and lesser apes live in separate parts of the world. Most great apes live in Africa, with the exception of orangutans which live in Sumatra and Borneo, and humans who live all over the world. The lesser apes are only found in southeast Asia on the mainland and on islands such as Sumatra, Borneo and Java. Wild apes all tend to live in tropical forest habitats with lesser apes spending most of their lives in the trees. The great apes, with the exception of orangutans, tend to be more terrestrial although they can all climb.
The general diets of the two families are slightly different. Lesser apes are mostly vegetarian, while great apes are omnivores. The lesser apes feed mainly on fruits such as figs as well as the shoots and leaves of various plants. They will also eat insects and small vertebrates as well as bird eggs. Orangutans do have a similar diet but gorillas, chimps and humans have more meat in their diets and will actively hunt animals for food.
Most species of apes live in small family groups. This is the case for all the lesser apes who are found in troops of 2 to 6 animals. In the great ape family, gorillas and chimps are also social animals, while orangutans are solitary in their habits and humans, of course, can be either. The more complex social interactions of the human species make us more distinct from our wild relatives.
References:
http://www.worldwildlife.org/species/finder/mountaingorilla/WWFBinaryitem12893.pdf
http://nationalzoo.si.edu/animals/primates/facts/default.cfm
http://animaldiversity.ummz.umich.edu/site/accounts/information/Hominidae.html
http://animaldiversity.ummz.umich.edu/site/accounts/information/Hylobatidae.html
