Social structure and life‐history patterns in western gorillas (Gorilla gorilla gorilla)

Abstract

Life-history traits and ecological conditions have an important influence on primate social systems. Most of what we know about the life-history patterns and social structure of gorillas comes from studies of eastern gorillas (Gorilla beringei sp.), which live under dramatically different ecological conditions compared to western gorillas (Gorilla gorilla sp.). In this paper we present new data on western gorilla social structure and life histories from four study sites, and make comparisons with eastern gorilla populations. Data were obtained from two study sites with gorilla groups undergoing the habituation process (Lossi, Democratic Republic of Congo and Bai Hokou, Central African Republic) and two "bai" studies (Maya Nord and Mbeli Bai, Republic of Congo). The size and structure of these groups were similar to those seen in eastern gorillas. However, differences in the occurrence of various group transitions (group formations, changes between one-male and multimale composition, and group disintegrations) exist, and western gorillas notably exhibit much higher rates of male emigration and correspondingly fewer multimale groups compared to mountain gorillas. Certain phenomena have been observed only rarely, including predation by leopards. The preliminary data show no significant differences in birth rates between western gorillas and mountain gorillas. The ecological variability across gorilla habitats likely explains the flexibility in the social system of gorillas, but we need more information on the social relationships and ecology of western gorillas to elucidate the causes for the similarities and differences between western and eastern gorillas on the levels of individuals, social groups, and population dynamics.

Noninvasive Follow-Up of Simian Immunodeficiency Virus Infection in Wild-Living Nonhabituated Western Lowland Gorillas in Cameroon

“…Between 2010 and 2011, follow-up missions were conducted at shorter intervals, and as a consequence, resampling of individuals and groups increased accordingly. The identified social groups had overlapping home ranges and varied in size from 2 to 15 individuals, with different male/female sex ratios, which is typical of western lowland gorillas (1,15,43). We determined the SIV infection rates (13 to 29%) in four identified nonhabituated social groups.…”

Origin and Biology of Simian Immunodeficiency Virus in Wild-Living Western Gorillas

“…Western lowland gorillas live in family units of 2 to 30 individuals which typically comprise one dominant male (silverback), three or more sexually active adult females, their offspring, and possibly a few nondominant males (27,42,62,67). The silverback mates with all adult females in the group (27,48). Adolescent males typically leave their natal groups and become solitary (and highly mobile) until they form their own harems (23), while females also transfer between groups (63).…”

Allostatic load and biological anthropology

“…Western lowland gorillas commonly live in polygynous groups with a single silverback (Bradley, Doran-Sheehy, & Vigilant, 2007;Doran & McNeilage, 1998 Nadler, Herndon, & Wallis, 1986;Robbins, 2007;Robbins et al, 2004;Watts, 2012;Yamagiwa, Basabose, Kaleme, & Yumoto, 2003). While all females are submissive to the silverback, they also exercise considerable mate choice and may freely disperse to a new silverback during intergroup encounters.…”