- Suborder: Haplorrhini
- Infraorder: Simiiformes
- Superfamily: Hominoidea
- Family: Homindae
Gorillas can be split into two species Gorilla beringei (Eastern gorilla) and Gorilla gorilla (Western lowland gorillas). Western and eastern gorillas are very phenotypically similar, however they differ in dentition and craniometrical measurements as well as genetically (Rowe, 1996; Nowak 1999). However both species have several shared characteristics. This includes dark brown to black fur and black skin. The males have large sagittal crest. Males will also develop a silver coloration (silverbacks) from their shoulders and rump. Gorillas are sexually dimorphic and tend to outweigh females by two hundred to three hundred ponds (Tutin et al. 1996; Rowe, 1996).
Gorilla gorillas are called Western and Lowland gorillas because of their location in the western lowlands of Equatorial Africa. Western gorillas are split into two subspecies, Gorilla gorilla gorilla (Western lowland gorilla) and Gorilla gorilla diehli (Eastern lowland gorilla) (Deblase & Martin, 1981; Wilson and Reeder, 1993).
Lowland gorillas live in tropical secondary forest (Deblase & Martin, 1981; MacDonald, 1987).
Lowland gorillas live in groups of 5 to 15 individuals with one dominant male, females and their young. However, a smaller group of less dominant males will often be at the periphery of the core group. If a male is displaced from his group by another male gorilla they will typically leave the group and remain solitary (MacDonald, 1987; Walker, 1975). Another group structure is of multi male groups that will occur during brief times in which males do not belong to social groups of dominant males and females (Yamagiwa et al. 2003). Both sexes tend to disperse from groups however females appear to disperse far more then males (Watt, 1996). Males that remain in their natal groups will be subordinate to the silverback of their group but they may have opportunities to mate with females in the group or becoming dominant male after the silverback dies (Yamagiwa & Kahekwa, 2001).
The mating structure of lowland gorillas is polygynous. A single dominant male will mate with the females. Males become dominant through fighting abilities and overall ability to protect the females and their infants. If a new male displaces the old male, the new male may systemically kill the infants so the mother’s will no longer be nursing and thus start their reproductive cycling. This allows for the new male to reproduce offspring due to his uncertainty of tenure within the group (MacDonald, 1987; Walker, 1975).
Lowland gorillas have no seasonal breeding time and will menstruate every 28 days. Females will have a single infant every four years. The infant will nurse 3 to 4 years. Generally females will start having infants at ten years of age. Males because of intense competition will likely breed at the age of 15 or older (MacDonald, 1987; Walker, 1975). Females are the main providers of the infants. They provide transportation, food and socialization. However, males provide protection (MacDonald, 1987; Walker, 1975). Females will initiate copulation via pursing their lips and approaching males while maintaining prolonged eye contact. If the male does not react she will reach for him, touch him or slap the ground (Sicotte, 2001). Male can also initiate copulations by displaying at her or touching her (Watts, 1991).
Behaviorally are lowland gorillas are peaceful and shy. Males will however react aggressively when intruders are close to their social groups. Males will stand erect and beat their chests to intimidate and show their strength. Males will also charge each other but will rarely hit each other and instead charge while rushing past (MacDonald, 1987; Walker, 1975). Other behaviors expressed by males include hooting which acts as an alarm to the group members to be alert MacDonald, 1987; Walker, 1975).
Lowland gorillas will build day and night nests. Lowland gorillas are also diurnal and spend most of their days eating (MacDonald, 1987; Walker, 1975). Gorillas tend to eat stemmed plants, leaves, berries, fern and fibrous barks (MacDonald, 1987; Walker, 1975). The subspecies also differs in diet. For example eastern lowland gorillas depend heavily on fruit and they also eat ants (Yamagiwa et a. 1994). Both subspecies of lowland gorilla will also eat termites and ants (Tutin, 1996).
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