![]() ![]() ![]() Dispersal also includes involuntary transfers, in which an immature male joins a new group following the disintegration of his previous group, typically due to the death of the silverback. Dispersal includes males who emigrate to become solitary, as well as males who leave their group with other gorillas as part of a group fission (Stoinski et al. Variation in male dispersal patterns has implications for group structure and possible variation in male tenure length and reproductive success between the two species (Robbins and Robbins 2018).įor male mountain gorillas, the first decision of their reproductive career is whether to disperse or remain philopatric (Fig. Because multimale groups form as a result of male philopatry and not takeovers by outsider males, multimale groups in western gorillas are extremely rare in comparison to both mountain gorilla populations that contain about 40% multimale groups (Robbins et al. In contrast, male western gorillas appear to have universal male dispersal (Robbins et al. Mountain gorillas are an interesting species in which to examine patterns of male dispersal and reproductive careers because they exhibit both philopatry and dispersal, which may lead to variation in male reproductive success (Harcourt 1978 Robbins 1995 Robbins et al. For example, in societies where male rank influences reproductive success, dispersal strategies may be determined by the viability of attaining the alpha position via tactics such as challenging a current dominant male, forming a new group by attracting females, or a group fission (van Noordwijk and van Schaik 2004). In primates, components of maturation and male dispersal patterns can have implications for the reproductive careers and variance in reproductive success of individual males (Alberts 2012 Alberts and Altmann 1995 Port et al. 2015 Koenig and Borries 2012 Ostro et al. 2015) or both philopatry and dispersal (Chowdhury et al. Despite most primate species exhibiting universal male dispersal (Pusey and Packer 1987), some species have universal male philopatry (Furuichi et al. In social living species, such as primates, dispersal patterns result in within- and between-species variation in social organization (Chapman and Rothman 2009 Kappeler and van Schaik 2002 Pusey and Packer 1987). Furthermore, the future success of dispersing individuals may vary, depending on the age at dispersal as well as the opportunities to acquire mates outside of the natal group (Clutton-Brock 2016 Davidian et al. Dispersal decisions and dispersal distance are influenced by many factors including reproductive opportunities, risk of inbreeding, competition for resources, and ecological conditions (Clutton-Brock 2016 Gilroy and Lockwood 2012). ![]() 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.ĭispersal is a key event in the life of an animal because of the linkages to population dynamics, life history strategies, genetic and social structuring of a population, and variance in reproductive success (Dobson 2013 Greenwood 1980). 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. 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. 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. 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. 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. However, little is known about the relationship between male dispersal or philopatry and reproductive careers in Bwindi mountain gorillas. Male mountain gorillas exhibit both philopatry and dispersal, resulting in a mixed one-male and multimale social organization. Dispersal is a key event in the life of an animal and it influences individual reproductive success. ![]()
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