This paper is a comparative study of two primates: ateles and avahi. Ateles’ common name is spider monkeys. It has an average size of 14-26 inches, an average weight of 13.25 lbs, and the average life span of 22 years. Ateles live in the tropical rainforests in South and Central America (National Geographic, 2018). Most ateles are black in color, but there are also brown and grey individuals in the sub-species. One of the most distinguished features of ateles is their gripping tails, acting almost like a fifth limb. The tails help ateles to hold on tightly to the braches even during their sleep. Avahi, with the common name Woolly indri, it a species found in Madagasgar. It has an average weight of about 2.2 lbs, and an average size of 14 inches. Avahi are greyish brown in color, with limbs in reddish brown. They have relatively short hands and longer feet. The subspecies of avahi include Avahi unicolor, Avahi occidentalis, and Avahi laniger, which reside in the eastern and western forests in Madagascar. In the western regions of the island, the sub-species of avahi is being endangered due to the excessive hunting and destruction of their natural habitat due to human activities (Primate Info Net, 2011).
Primates have a set of traits that classify them into the primate order. In the mammal class, primates are the ones that have “collar bones and grasping fingers (Lecture Notes).” Their thumbs are usually opposable relative to the other four fingers (or toes). This feature enables primates to grip onto things with their hands or feet. Both ateles and avahi have this feature with their hands and feet. Primates have short faces, small noses and eyes positioned backwards. Their sight line is pointing forward. These features give them a decreased sense of smell and a three-dimensional vision that is able to sense depth (Lecture Notes). Primates have a combination of cutting, crushing, and grinding teeth, which enable them to have a diversified source of food, including insects, fruits, and leaves. Primates are also able to make sounds for the purpose of communication. The relatively advanced brain among mammals make primate one of the most sophisticated and intelligent orders. Their highly developed brains enable them to have facial expressions, social behaviors, and advanced emotions. The dependency on social behavior of primates generates a series of features, including longer gestation (over 7 months for ateles, 5 months for avahi), less babies, delayed maturation, dependency on learned behaviors, and social group living (Lecture Notes). These features are found in both ateles and avahi, which classify them as primates.
Ateles have slim, long arms that help them hop on the treetops freely. Their tails are able to grip onto the branches as well, making it easy for them to move quickly in the forest (National Geographic, 2018). The tails of ateles can be as long as 35 inches, even longer than their bodies. There are extremely developed and act as hands functionally to grip onto the branches. The long hands and flexible tails are the main adaptive features of ateles, since an extensive amount of climbing is required to survive in the tropical forests. The most specialized features of avahi are the small body size and large eyes relative to its face. Despite being of approximate lengths, the weight of the avahi is only about one sixth of the ateles. This small body size is adaptive because it is easier for smaller animals to survive in adverse environment, they eat less, and are more difficult to be spotted by the natural enemies. The large eyes of the avahi are adaptive as well, since the animal is nocturnal (Thalmann, 2001). Large eyes enable better night vision by letting in more light. This gives the avahi a better chance to find food at night.
Ateles have social behaviors to gather in groups of two to three dozen. These large groups split into smaller groups at night, with several ateles sleeping close to each other. These smaller groups also feed together, searching in the treetops for nuts, fruits, and eggs. It has been found that spider monkeys in San Juan modify certain aggression behaviors in the habitats with a higher ateles density (Abondano & Link, 2012). These social behaviors are an adaptive response to the fragmentation and loss of habitats, because hunting in groups increases the chance of safety and survival than solitude. For avahi, a stable monogamous pattern has been found to be a social adaptation to limited resources (Thalmann, 2001). Since avahi is limited in all seasons in the resources, they tend to repeatedly exploit the “under-represented resources.” Limitation in the resources makes it worth to defend a location of food resources. Female avahi are inclined to stick to one spouse because they have already established a sense of familiarity over it (Thalmann, 2001). And the cooperative mode of a pair of avahi may be the safest and most stable. The shared knowledge of the location and the motivation to defend the resources make the monogamy the opti