Abstract:When mothers continue to support their offspring beyond infancy, they can influence the fitness of those offspring, the strength of social relationships within their groups, and the life-history traits of their species. Using up to 30 years of demographic data from 58 groups of gorillas in two study sites, this study extends such findings by showing that mothers may also contribute to differences in social organization between closely related species. Female mountain gorillas remained with their sons for signi… Show more
“…Thus, when comparing the influence of the distributions of females on the distribution of males in groups in each gorilla species, it may be insightful to consider only the groups that contain potential male emigrants (i.e., multimale groups), rather than all groups. When considering only multimale groups (and excluding all‐male groups), the number of adult females in multimale groups was 5.3 ± 3.2 for mountain gorillas versus 1.6 ± 0.67 for western gorillas, which is greater than the difference for all groups (previous paragraph) . Thus, when focusing on groups with potential male emigrants (multimale groups), the comparison between gorilla species provides greater support for the hypothesis that the distribution of males is ultimately determined by the distribution of females …”
Section: Hypotheses For Variation In Social Organizationmentioning
confidence: 83%
“…The lack of immigration means that male philopatry is the primary proximate reason for the occurrence of multimale groups. In other words, multimale groups are rare among western gorillas because all of the subordinate males disperse as they reach adulthood …”
Section: Introductionmentioning
confidence: 99%
“…Approximately 5% of western gorilla groups and 5% of Grauer's gorilla groups are multimale (Table ) . Initially, multimale groups were thought to be only a temporary phase prior to the emigration of maturing males, creating what has also been referred to as “age‐graded groups.” This appears to be what occurs in western gorillas . However multimale groups in mountain gorillas are not simply a short, transient stage as males reach maturity and then eventually emigrate, but rather are more common and long‐lasting than initially expected with mature silverback males sometimes coresiding for a decade or longer …”
A focus of socioecological research is to understand how ecological, social, and life history factors influence the variability of social organization within and between species. The genus Gorilla exhibits variability in social organization with western gorilla groups being almost exclusively one‐male, yet approximately 40% of mountain gorilla groups are multimale. We review five ultimate causes for the variability in social organization within and among gorilla populations: human disturbance, ecological constraints on group size, risk of infanticide, life history patterns, and population density. We find the most evidence for the ecological constraints and life history hypotheses, but an over‐riding explanation remains elusive. The variability may hinge on variation in female dispersal patterns, as females seek a group of optimal size and with a good protector male. Our review illustrates the challenges of understanding why the social organization of closely related species may deviate from predictions based on socioecological and life history theory.
“…Thus, when comparing the influence of the distributions of females on the distribution of males in groups in each gorilla species, it may be insightful to consider only the groups that contain potential male emigrants (i.e., multimale groups), rather than all groups. When considering only multimale groups (and excluding all‐male groups), the number of adult females in multimale groups was 5.3 ± 3.2 for mountain gorillas versus 1.6 ± 0.67 for western gorillas, which is greater than the difference for all groups (previous paragraph) . Thus, when focusing on groups with potential male emigrants (multimale groups), the comparison between gorilla species provides greater support for the hypothesis that the distribution of males is ultimately determined by the distribution of females …”
Section: Hypotheses For Variation In Social Organizationmentioning
confidence: 83%
“…The lack of immigration means that male philopatry is the primary proximate reason for the occurrence of multimale groups. In other words, multimale groups are rare among western gorillas because all of the subordinate males disperse as they reach adulthood …”
Section: Introductionmentioning
confidence: 99%
“…Approximately 5% of western gorilla groups and 5% of Grauer's gorilla groups are multimale (Table ) . Initially, multimale groups were thought to be only a temporary phase prior to the emigration of maturing males, creating what has also been referred to as “age‐graded groups.” This appears to be what occurs in western gorillas . However multimale groups in mountain gorillas are not simply a short, transient stage as males reach maturity and then eventually emigrate, but rather are more common and long‐lasting than initially expected with mature silverback males sometimes coresiding for a decade or longer …”
A focus of socioecological research is to understand how ecological, social, and life history factors influence the variability of social organization within and between species. The genus Gorilla exhibits variability in social organization with western gorilla groups being almost exclusively one‐male, yet approximately 40% of mountain gorilla groups are multimale. We review five ultimate causes for the variability in social organization within and among gorilla populations: human disturbance, ecological constraints on group size, risk of infanticide, life history patterns, and population density. We find the most evidence for the ecological constraints and life history hypotheses, but an over‐riding explanation remains elusive. The variability may hinge on variation in female dispersal patterns, as females seek a group of optimal size and with a good protector male. Our review illustrates the challenges of understanding why the social organization of closely related species may deviate from predictions based on socioecological and life history theory.
“…Automated identification software could assist the manual identification process. Particularly, since group stability of western gorillas is low, individuals transfer between groups regularly, groups are formed or dissolved, and groups or individuals may immigrate in, or emigrate out of the bai population [72,57,62]. When unknown individuals appear in the bai, it can be challenging to establish with certainty if they are truly new to the population or if they were already known to prior research teams [5].…”
In this paper we report on the context and evaluation of a system for an automatic interpretation of sightings of individual western lowland gorillas (Gorilla gorilla gorilla) as captured in facial fieldVisual data acquisition in the field often captures sufficient information to establish encounters with individual gorillas. However, relevant information is locked within the pixel patterns measured, usually requiring expert knowledge and time-consuming efforts for identification. Computer vision can help to extract gorilla identities by performing automated species detection, followed by individual facial identification. We show that standard deep learning models combined with a traditional SVM classifier can be used for this task. To assist encounter processing, predictions can be presented graphically with known population information as shown.
“…The probability of male emigration does not appear to be influenced by the number of potential mates in the group, the number of potential competitors, or the age of dominant male (Stoinski et al 2009a; Watts 2000). Instead, mating opportunities and the presence of mothers may lead to male philopatry (Robbins et al 2016; Stoinski et al 2009a, b). Fig.…”
Dispersal is a key event in the life of an animal and it influences individual reproductive success. Male mountain gorillas exhibit both philopatry and dispersal, resulting in a mixed one-male and multimale social organization. However, little is known about the relationship between male dispersal or philopatry and reproductive careers in Bwindi mountain gorillas. Here we analyze data spanning from 1993 to 2017 on social groups in Bwindi Impenetrable National Park, Uganda to examine the proportion of males that disperse, age of dispersal, pathways to attaining alpha status, fate of dispersing males and philopatric males, and male tenure length as well as make comparisons of these variables to the Virunga mountain gorilla population. We report previously undocumented cases of dispersal by immature males and old males and we also observed the only known case of a fully mature male immigrating into a breeding group. We used genetic tracking of known individuals to estimate that a minimum of 25% of males that disperse to become solitary males eventually form new groups. No differences were found between the Bwindi and Virunga population in the age of male dispersal, the proportion of males that disperse, the age of alpha male acquisition, and dominance tenure length. The lack of differences may be due to small sample sizes or because the observed ecological variability does not lead to life history differences between the populations. Males in both populations follow variable strategies to attain alpha status leading to the variable one-male and multimale social organization, including dispersal to become solitary and eventually form a group, via group fissioning, usurping another alpha male, or inheriting the alpha position when a previous group leader dies.
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