Individualistic female dominance hierarchies with varying strength in a highly folivorous population of black-and-white colobus

Abstract

Females that do not experience strong contest competition for food are presumed to form 'egalitarian' relationships (i.e., lacking strong, linear dominance hierarchies). However, recent studies of Gorilla beringei beringei (mountain gorilla) have documented relatively strong, linear female dominance hierarchies despite them having a highly folivorous diet that generates relatively low levels of within-group contest competition (Robbins et al., 2005(Robbins et al., , 2007. To investigate if this pattern holds true for other highly folivorous species that may experience low levels of contest competition, we examined the linearity and strength of female dominance hierarchies in a population of Colobus vellerosus (ursine colobus or white-thighed colobus) at Boabeng-Fiema, Ghana. From 2004 to 2011, we collected data via ad libitum and focal sampling of 75 adult and subadult females in eight groups. Half of the study groups had few unknown submissive relationships, and females formed individualistic hierarchies with high linearity indices ranging from 0.9 to 1. There was between-group variation in all components of hierarchical strength (i.e., hierarchical expression, consistency, and stability). Groups showed varying rates of submission, and there was a short latency to detect a linear hierarchy in some groups and a long latency in other groups (i.e., varying levels of hierarchical expression). Females in most groups formed unidirectional and stable relationships. Maturing females challenged older females in some groups, and these groups had more non-linear relationships (i.e., dyads with more submissive interactions down rather than up the hierarchy) and higher rates of individual rank change than other groups. Based on low rates of submission, long latencies, and/or some inconsistencies, we conclude that most groups form relatively

Kinship and similarity in residency status structure female social networks in black‐and‐white colobus monkeys (colobus vellerosus)

“…Females with similar dominance ranks were less aggressive toward each other in a group with long-term hierarchical stability (Wikberg et al, 2013). In contrast, females with similar dominance ranks were more aggressive toward each other in one group with a less stable dominance hierarchy.…”

“…Maturational stage was not included as a predictor variable when analyzing the social networks in NP, OD, and RT group because these groups only contained adult females. We used submissive interactions (e.g., avoid, displace, flee, grimace, present, and snuffling vocalizations) collected ad libitum and during focal samples to determine the females' dominance ranks (Wikberg et al, 2013). The majority of dyads (96%) formed unidirectional submissive relationships, and we did not detect any rank changes during our study period (Wikberg et al, 2013).…”

“…We used submissive interactions (e.g., avoid, displace, flee, grimace, present, and snuffling vocalizations) collected ad libitum and during focal samples to determine the females' dominance ranks (Wikberg et al, 2013). The majority of dyads (96%) formed unidirectional submissive relationships, and we did not detect any rank changes during our study period (Wikberg et al, 2013). We used Elo-ratings to compute females' probabilistic dominance ranks (Neumann et al, 2011), and we standardized each female's rank by dividing it by the maximum rank in each group.…”

“…[Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] (Wikberg et al, 2013). Therefore, it is possible that close-ranking females were more aggressive toward each other either to ascertain their new dominance rank or as an attempt to increase in rank.…”

“…We focus here on a species with a different social structure, Colobus vellerosus (white-thighed colobus or ursine colobus). Females in our study population form individualistic dominance hierarchies of intermediate strength (Wikberg et al, 2013), show facultative dispersal (Teichroeb et al, 2009;Wikberg et al, 2012), and have varying access to female kin . These traits likely lead to a situation where dominance rank, kinship, and residency status do not always correspond with each other, in contrast to the common pattern in cercopithecines and hyenas.…”