Within-group Contest Research Articles

Social drivers of maturation age in female geladas.

Female reproductive maturation is a critical life-history milestone, initiating an individual's reproductive career. Studies in social mammals have often focused on how variables related to nutrition influence maturation age in females. However, parallel investigations have identified conspicuous male-mediated effects in which female maturation is sensitive to the presence and relatedness of males. Here, we evaluated whether the more "classic" socioecological variables (i.e., maternal rank, group size) predict maturation age in wild geladas-a primate species with known male-mediated effects on maturation and a grassy diet that is not expected to generate intense female competition. Females delayed maturation in the presence of their fathers and quickly matured when unrelated, dominant males arrived. Controlling for these male effects, however, higher-ranking daughters matured at earlier ages than lower-ranking daughters, suggesting an effect of within-group contest competition. However, contrary to predictions related to within-group scramble competition, females matured earliest in larger groups. We attribute this result to either: 1) a shift to "faster" development in response to the high infant mortality risk posed by larger groups; or 2) accelerated maturation triggered by brief, unobserved male visits. While earlier ages at maturation were indeed associated with earlier ages at first birth, these benefits were occasionally offset by male takeovers, which can delay successful reproduction via spontaneous abortion. In sum, rank-related effects on reproduction can still occur even when socioecological theory would predict otherwise, and males (and the risks they pose) may prompt female maturation even outside of successful takeovers.

Patterns of female social relationships in a primate with female-biased dispersal

In socially living mammals, females often form highly differentiated and stable social relationships, commonly with genetically related individuals, which leads to social clusters within groups (i.e. matrilines). However, in primates, research on female social relationships commonly focuses on species and populations with female philopatry and the frequent occurrence of affiliative and agonistic behaviours. Therefore, our aim was to investigate the long-term patterns of female social relationships in a primate with female-biased dispersal, where affiliative and agonistic behaviours among females are rare. We analysed 9 years of continuous data from female Ugandan red colobus monkeys, Piliocolobus tephrosceles , in Kibale National Park, Uganda, and used spatial proximity to establish social networks for 3- and 6-month periods. Then, we investigated the differentiation, stability and clustering of social relationships for each of these periods using several approaches. As expected for a primate with female-biased dispersal, our results largely confirmed the absence of temporally stable social relationships and social clusters within the group. However, in about half of the analysed time periods, females formed differentiated social relationships. This indicates that factors other than dispersal patterns and within-group contest competition contribute to the formation of the ephemeral relationships, as measured by spatial proximity, among female red colobus. Therefore, our results on the patterns of female social relationships in a primate with female-biased dispersal provide important empirical insight for the refinements of theories that aim to explain social evolution in mammals. • We analysed female social relationships over 9 years in a female-dispersed primate. • Females formed differentiated relationships during half of the analysed periods. • There was little indication for temporally stable relationships among females. • Females did not form social clusters often observed in primates with matrilines.

Be early or be tolerated: vervet monkey, Chlorocebus pygerythrus, foraging strategies in a dispersed resource

Among social foragers, individuals can actively search for and find food (the producers) or join already discovered food patches (the scroungers). Compared to scroungers, producers often occupy more dangerous outer spatial positions in the group, but they benefit from the finder's advantage, which is the amount of food eaten before the arrival of others. Scroungers may occupy safer positions but they face feeding competition when joining a patch already occupied by others. Here, we report factors influencing intragroup spatial position, feeding strategies and feeding success for a group of wild vervet monkeys, C. pygerythrus, at Lake Nabugabo, Uganda. We collected data using behavioural observations and field experimentation (N = 132 trials) where we set up an artificial food patch with dispersed food rewards. We found that individuals who spent more time in the front-outer position of a moving group produced more. Producers that had a greater finder's time advantage (fed undetected by group members for longer periods) had a greater finder's advantage (consumed more food items before the arrival of other group members), and scroungers that arrived earlier had greater overall feeding success. We found that when the scrounger was higher ranking than other individuals at the patch, they used displacement scrounging (supplanted at least one individual from the patch to gain access to the food resource). However, feeding success did not differ between displacement scrounging and tolerated scrounging (when the scrounger fed at the patch with at least one other individual). Interestingly, we did not find higher-ranking individuals to have greater feeding success than lower-ranking individuals. Our findings corroborate previous studies showing that even among species with a linear dominance hierarchy and high occurrences of within-group contest competition, dominant individuals do not benefit from feeding advantages at large, dispersed food patches since they cannot monopolize the resource. Furthermore, our results emphasize the need to understand factors influencing feeding tolerance, particularly for subordinate individuals, who need to process ecological and social elements to maximize their food acquisition.

How socio-ecological factors influence the differentiation of social relationships: an integrated conceptual framework.

The extent of differentiation of social relationships within groups is a means to assess social complexity, with greater differentiation indicating greater social complexity. Socio-ecological factors are likely to influence social complexity, but no attempt has been made to explain the differentiation of social relationships using multiple socio-ecological factors. Here, we propose a conceptual framework based on four components underlying multiple socio-ecological factors that influence the differentiation of social relationships: the extent of within-group contest competition to access resources, the extent to which individuals differ in their ability to provide a variety of services, the need for group-level cooperation and the constraints on social interactions. We use the framework to make predictions about the degree of relationship differentiation that can be expected within a group according to the cumulative contribution of multiple socio-ecological factors to each of the four components. The framework has broad applicability, since the four components are likely to be relevant to a wide range of animal taxa and to additional socio-ecological factors not explicitly dealt with here. Hence, the framework can be used as the basis for the development of novel and testable hypotheses about intra- and interspecific differences in relationship differentiation and social complexity.

Do males bond? A study of male-male relationships in Nicobar long-tailed macaques Macaca fascicularis umbrosus

In primates, males compete for a mate, which is a non-sharable resource. This makes the conditions less conducive for males to have stable relationships. One such special kind of relationship is a bond where the interactions are reciprocated, equitable and differentiated. Bonds in macaque societies are based on the degree of within-group contest competition for mates which is dependent on the synchronization of female fertile phase and reliability of fertility signals. Species of the Fascicularis group, including Nicobar subspecies, show intermediate reliability in the signals with mild peaks, and studies have shown reciprocity but no differentiation. We conducted a study on a group of wild Nicobar long-tailed macaques Macaca fascicularis umbrosus to understand the existing patterns of male-male relationships. We examined whether there is reciprocity in affiliation among the individuals and whether the rate of affiliation is balanced. We also measured the dominance linearity and steepness in the group to understand the monopolizability of females. We used social network analysis to understand whether the relations are differentiated based on hierarchical position and whether the high-ranking individuals are the most central individuals in the distribution of grooming in the group. We found that there is reciprocity among the males although that is not equitable. There was no rankrelated differentiation of affiliation among the males of the group. Instead, the identities of individuals influenced affiliation patterns. Our results correspond to the existent strong relationships but lack of social bond otherwise found in the Fascicularis group of macaques.

Behavioural Variability in Macaques and Langurs of the Western Ghats, India

Studies that compare differences in the behavioural variability across species and genera are rare among south Asian primates. Such studies are important for understanding within-group feeding competition in primates as interindividual difference in frequency of behaviour is a good indicator of feeding competition. We compared the variability in individual activities of lion-tailed macaques, bonnet macaques, Nilgiri langurs, and black-footed grey langurs. Both macaque species showed variability in their activities, with bonnet macaques showing higher variability than lion-tailed macaques. This indicated higher within-group competition in bonnet macaques than in lion-tailed macaques. Folivorous Nilgiri langurs and black-footed grey langurs did not show variability in any behaviour, indicating weak or negligible within-group competition. Except in the bonnet macaque, the interindividual differences in activities in the other species were potentially due to the differences between lactating and non-lactating females. We observed that langurs were less variable than macaques, indicating higher within-group competition in macaques than in langurs. We also observed a higher frequency of aggressive interactions during feeding among macaques than langurs, substantiating higher within-group competition in macaques than in langurs. We further discuss the different possibilities of within-group contest and scramble competition in these species.

Understanding stable bi-female grouping in gibbons: feeding competition and reproductive success.

IntroductionSpecies of the order Primates are highly gregarious with most species living in permanent heterosexual social groups. According to theory in socioecology maximum social group size is limited by rates of intra-group feeding competition and associated increases in travel costs. Unlike other hylobatids, which are predominantly pair living, cao vit gibbons (Nomascus nasutus), and two other species of crested gibbon (Nomascus spp.) living in northern seasonal forest, regularly exhibit larger bi-female groups. To better understand the ability of northern gibbons to live in stable bi-female groups, we examined food distribution, feeding competition and reproductive success over a period of six years in a small cao vit gibbon population at Bangliang, Guangxi, China.ResultsIn general, we found weak evidences for within-group contest or scramble competition in our two study groups, which we attribute to high spatial and temporal heterogeneity in the distribution of their important food species. Nevertheless, the larger of the two groups studied increased feeding time and group spread during lean periods, factors that may limit cao vit gibbon group size to a maximum of two breeding females. Relative to tropical pair-living gibbons, there is no evidence that cao vit gibbons travel farther or spend more time feeding, but they did consume more leaves and buds and less fruit and figs. Despite their highly folivorous diet, the average inter-birth interval is comparable to tropical gibbon populations, and the survival rate of infants and juveniles in our study groups is high.ConclusionCao vit gibbons do not suffer obvious costs in terms of feeding competition and reproductive success by living in bi-female groups, but within-group feeding competition may determine the upper the limit of cao vit gibbon group size to a maximum of two breeding females. These findings contribute to a growing body of evidence that bi-female grouping can be a stable grouping pattern of gibbons in certain habitats and further emphasize the flexibility of gibbon social organization.

Group size, contest competition, and social structure in Cayo Santiago rhesus macaques

In non-human primate systems, the Ecological Model of Female Social Relationships (EMFSR) views variation in female social structure as adaptations to variation in recent past and/or current ecological conditions. Group size may be a major additional demographic factor affecting social structure through its effects on resource competition. In particular, in Resident Nepotistic Despotic (RND) societies, when resources are uniformly clumped, larger groups are expected to face higher levels of within-group contest competition (WGC) than smaller groups and to respond by showing more highly despotic social relationships than smaller groups. On the other hand, smaller groups are expected to face higher levels of between-group contest competition (BGC) and hence, show greater levels of intragroup tolerance (or lower despotism). While formal models do not explicitly predict this kind of variation within species, many researchers have investigated such intraspecific variation. Thus, we tested these predictions across three groups of free-ranging rhesus macaques (Macaca mulatta) of varying sizes on Cayo Santiago, Puerto Rico, where we were able to control for variation in resource-patch contestability and predation risk. Subjects were adult females. For each group, we collected data on (1) exposure and (2) behavioural reactions to WGC and BGC at two independent sets of clumped resources (feeding corrals and drinking stations) and (3) agonistic and affiliative social behaviour, using focal animal, all occurrences, and ad-libitum sampling methods. As predicted, our largest group showed the greatest levels of exposure and behavioural responses to WGC contexts. Likewise, our smallest group showed greatest levels of exposure and responses to BGC contexts. However, aspects of social structure did not vary across groups in directions predicted by the EMFSR. These findings are broadly consistent with several previous comparative tests of the model on other primate taxa that found strong links between group size, ecological factors and contest competitive regimes, but little or no evidence of links with social structure. Our study adds strength to these conclusions given our unique ability to control for several variables on Cayo Santiago. We suggest that our findings may be generalizable to several wild rhesus populations in North India, given that they have lived in similarly dense populations and have been frequently provisioned by humans for thousands of years.

Shirts Today, Skins Tomorrow: Dual Contests and the Effects of Fragmentation in Self-Determination Disputes

While theoretical models of conflict often treat actors as unitary, most self-determination groups are fragmented into a number of competing internal factions. This article presents a framework for understanding the dual contests that self-determination groups engage in — the first with their host state and the second between co-ethnic factions within groups. Using a new data set of the number of factions within a sample of self-determination groups from 1960 to 2008, the authors find that competition between co-ethnic factions is a key determinant of their conflict behavior. More competing factions are associated with higher instances of violence against the state as well as more factional fighting and attacks on co-ethnic civilians. More factions using violence increases the chances that other factions will do so, and the entry of a new faction prompts violence from existing factions in a within-group contest for political relevance. These findings have implications for both theory and policy.

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

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, 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

Socioecology of wild bearded capuchin monkeys (Sapajus libidinosus): an analysis of social relationships among female primates that use tools in feeding

Socioecology considers that the features of food sources affect female social relationships in group-living species. Among primates, the tests of socioecological models are largely focused on Old World species and do not evaluate if the use of feeding tools affects the competitive regime over food and females’ relations in wild populations. We studied female social relationships among a wild population of bearded capuchins monkeys (Sapajus libidinosus) that use percussive tools (stones) to crack encased foods, in a semi-arid habitat in Brazil. Females fed mainly on clumped, high quality resources, indicating that the habitat provides a high quality diet year-round. Females experienced contest competition within and between-groups. As predicted by socioecological models, females’ social relationships were characterized by philopatry, linear dominance hierarchies, coalitions, and tolerance in feeding bouts. Females spent a small proportion of their feeding time using tools. Nevertheless, tool sites generated high rates of contest competition and lower indices of tolerance among females. Although the social structure of our study population did not differ significantly from the pattern observed in wild populations of Sapajus that do not use tools, tool use increased within-group contest competition and apparently contributed to the linearity of the dominance hierarchies established among females. We predict that when tool use results in usurpable food resources, it will increase contest competition within group-living species.

Effects of age, reproductive state, and the number of competitors on the dominance dynamics of wild female Hanuman langurs

Female dominance hierarchies form as a result of individual differences in resource holding potential, social processes such as winner-loser effects or coalitions, and ecological conditions that favor contest competition. Contest competition is assumed to result in despotic, nepotistic, and stable hierarchies. However, female Hanuman langurs are exceptions to this pattern, with data from provisioned populations indicating despotic, yet individualistic (age-inversed) and unstable hierarchies despite strong within-group contest. We present data on hierarchical linearity, stability, and the determinants of female rank and rank change in a population of unprovisioned, wild Hanuman langurs (Ramnagar, Nepal). Based on 12 490 dyadic displacement interactions collected over 5 years from a medium-sized group (P group, mean = 6.9 adult females) and a large group (O group, mean = 13.6 adult females), stable periods (P group, ; O group, ) were identified and dominance hierarchies constructed with the program MatMan. In both groups, dominance hierarchies were linear (), with high directional consistency within dyads. Rank was negatively related with age, while the presence of maternal kin had no effect. Reproductive state affected dominance rank in the larger group, with females ascending the hierarchy prior to conception, and dropping in rank after birth. Ranks were unstable, with group size and the number of juvenile females driving the effect (GLMM, ). These results match earlier findings for provisioned populations. In female Hanuman langurs, competition seems most intense around conception and during gestation, creating rank instability, which is further exacerbated by the number of adult as well as maturing females.

Shirts Today, Skins Tomorrow

While theoretical models of conflict often treat actors as unitary, most self-determination groups are fragmented into a number of competing internal factions. This article presents a framework for understanding the “dual contests” that self-determination groups engage in—the first with their host state and the second between co-ethnic factions within groups. Using a new data set of the number of factions within a sample of self-determination groups from 1960 to 2008, the authors find that competition between co-ethnic factions is a key determinant of their conflict behavior. More competing factions are associated with higher instances of violence against the state as well as more factional fighting and attacks on co-ethnic civilians. More factions using violence increases the chances that other factions will do so, and the entry of a new faction prompts violence from existing factions in a within-group contest for political relevance. These findings have implications for both theory and policy.

Using biological markets principles to examine patterns of grooming exchange in Macaca thibetana

Biological markets principles offer testable hypotheses to explain variation in grooming exchange patterns among nonhuman primates. They predict that when within-group contest competition (WGC) is high and dominance hierarchies steep, grooming interchange with other "commodity" behaviors (such as agonistic support) should prevail. In contrast, when WGC is low and gradients shallow, market theory predicts that grooming reciprocity should prevail. We tested these predictions in a wild, provisioned Tibetan macaque (Macaca thibetana) group across six time periods during which the group had been subjected to varying degrees of range restriction. Data on female-female aggression, grooming, and support were collected using all-occurrences and focal animal sampling techniques, and analyzed using ANCOVA methods and correlation analyses. We found that hierarchical steepness varied significantly across periods, but did not correlate with two indirect indicators of WGC (group size and range restriction) in predicted directions. Contrary to expectations, we found a negative correlation between steepness and group size, perhaps because the responses of group members to external risks (i.e. prolonged and unavoidable exposure to humans) may have overshadowed the effects of WGC. As predicted, grooming reciprocity was significant in each period and negatively correlated with steepness, even after we controlled group size, kinship, rank differences, and proximity. In contrast, there was no evidence for grooming interchange with agonistic support or for a positive relationship between interchange and steepness. We hypothesize that stressful conditions and/or the presence of stable hierarchies during each period may have led to a greater market demand for grooming than support. We suggest that future studies testing these predictions consider more direct measures of WGC and commodities in addition to support, such as feeding tolerance and access to infants.

Females go where the food is: does the socio-ecological model explain variation in social organisation of solitary foragers?

The socio-ecological model (SEM) links ecological factors with characteristics of social systems and allows predictions about the relationships between resource distribution, type of competition and social organisation. It has been mainly applied to group-living species but ought to explain variation in social organisation of solitary species as well. The aim of this study was to test basic predictions of the SEM in two solitary primates, which differ in two characteristics of female association patterns: (1) spatial ranging and (2) sleeping associations. Beginning in August 2002, we regularly (re-)captured and marked individuals of sympatric populations of Madame Berthe's and grey mouse lemurs (Microcebus berthae, Microcebus murinus) in Kirindy Forest (Madagascar). We recorded data on spatial patterns, feeding and social behaviour by means of direct observation of radio-collared females. The major food sources of M. berthae occurred in small dispersed patches leading to strong within-group scramble competition and over-dispersed females with a low potential for female associations. In contrast, M. murinus additionally used patchily distributed, high-quality (large) resources facilitating within-group contest competition. The combined influence of less strong within-group scramble and contest as well as between-group contest over non-food resources allowed females of this species to cluster in space. Additionally, we experimentally manipulated the spatial distribution of food sources and found that females adjusted their spatial patterns to food resource distribution. Thus, our results support basic predictions of the SEM and demonstrated that it can also explain variation in social organisation of solitary foragers.

Formal submission, tolerance and socioecological models: a test with female Hanuman langurs

Patterns of agonistic relationships among group-living mammalian females are suggested to reflect differences in feeding competition. Socioecological models predict that within-group contest (WGC) competition leads to despotic relationships that are linear, consistent, and stable, in which subordinate individuals use formal submission to acknowledge rank. Between-group contest (BGC) competition and risk of infanticide are predicted to add tolerance, as evidenced by frequent reconciliation, low-intensity aggression and counteraggression. We examined the predicted effects for formal submission and two criteria of tolerance for a group of Hanuman langurs ( Semnopithecus entellus ) in a population known to experience WGC and BGC as well as high rates of infanticide. Results were based on focal animal sampling of eight of 13 adult females (419 h) and ad libitum sampling of all 13 females (711 contact hours) in the group Kailana I (Jodhpur, India). The behaviour ‘presenting’ ( N = 281) qualified as formal submission, adhering to most proposed criteria (e.g. linear, consistent, predictive of other agonistic relationships and hierarchies, 40.9% spontaneous). Thus, regarding formal submission, the predicted effects of WGC hold, and support the explanatory value of this aspect of socioecological models. In contrast, agonistic relationships were nontolerant, with frequent high-intensity aggression (48.9% of N = 231) and almost no counteraggression (

Social factors enhancing foraging success of a wild group of Japanese macaques (Macaca fuscata) in a patchy food environment

We evaluated the effects of social factors and food quality on patch use by a wild group of Japanese macaques (Macaca fuscata) that experienced no inter-group feeding competition or predation risk. We obtained the following results: (1) Food patch depletion and within-group scramble competition for food apparently did not affect patch use. (2) Within-group contest competition (aggressive interactions related to social-dominance rank) also did not strongly affect patch use. (3) The number of co-feeders in the same patch consistently showed positive effects on patch use, while food quality did not have consistent effects. These results suggest that the presence of co-feeders enhances foraging success in a patchy food environment.

Controversy over the application of current socioecological models to folivorous primates: Colobus vellerosus fits the predictions

We explore the applicability of the current socio-ecological model to characterize the social structure of Colobus vellerosus, a folivorous primate. The current socio-ecological model predicts that female social relationships should respond in predictable ways to food abundance and distribution and associated competitive regimes. It appears to successfully explain variation in social structure in some primate species; however, recent research indicates that several folivorous or folivore-frugivorous species seem to be exceptions. We present data on social relationships and social structure in two groups of C. vellerosus over 15 months at Boabeng-Fiema, Ghana. As predicted by the model, our results indicate the co-occurrence of 1) low levels of grooming between female C. vellerosus when compared with other species, 2) an absence of female coalitions over food, and 3) female dispersal. Taken together, these traits suggest a "Dispersal-Egalitarian" species. However, our results also indicate female-female affiliation was higher than male-female affiliation, which was more indicative of a "female resident" species. Our data also suggests inter-sexual affiliation varied among groups. This variation in inter-sexual affiliation could be due to variation in the intensity of infanticidal threats between groups. The combination of these social characteristics lead us to conclude that C. vellerosus' social structure is largely congruent with the ecological indicators of food distribution and female competitive regime that we have previously documented, which indicated high quality foods were not monopolizable or usurpable and behavioral evidence of within-group contest competition (i.e. supplantations over food) was rare. But the combination of higher female-female affiliation (compared to male-female) and female dispersal is difficult to explain in light of predictions, unless future work reveals female residency is more predominant than female dispersal in our population. We also discuss reasons why some folivores do not appear to fit the predictions of the current socio-ecological model.

Socioecological influences on the reproductive success of female mountain gorillas (Gorilla beringei beringei)

Over the past few decades, socioecological models have been developed to explain the relationships between the ecological conditions, social systems, and reproductive success of primates. Feeding competition, predation pressures, and risk of infanticide are predicted to influence how female reproductive success (FRS) depends upon their dominance rank, group size, and mate choices. This paper examines how those factors affected the reproductive success of female mountain gorillas (Gorilla beringei beringei) of the Virunga Volcanoes, Rwanda from 1967–2004. Reproductive success was measured through analyses of interbirth intervals, infant survival, and surviving infant birth rates using data from 214 infants born to 67 females. Mountain gorillas were predicted to have “within-group scramble” feeding competition, but we found no evidence of lower FRS in larger groups, even as those groups became two to five times larger than the population average. The gorillas are considered to have negligible “within-group contest” competition, yet higher ranked mothers had shorter interbirth intervals. Infant survival was higher in multimale groups, which was expected because infanticide occurs when the male dies in a one-male group. The combination of those results led to higher surviving birth rates for higher ranking females in multimale groups. Overall, however, the socioecological factors accounted for a relatively small portion of the variance in FRS, as expected for a species that feeds on abundant, evenly distributed foliage.

Rank differences in energy intake rates in white-faced capuchin monkeys, Cebus capucinus: the effects of contest competition

The effect of aggressive competition over food resources on energy intake rate is analyzed for individuals of three groups of 25–35 white-faced capuchin monkeys, Cebus capucinus, living in and near Lomas Barbudal Biological Reserve, Costa Rica. An individual’s energy intake rate on a given food species was affected by its rank and the number of agonistic interactions within the feeding tree. Dominant group members had higher energy intake rates relative to subordinate group members whether or not there was agonism within the feeding tree. Low- and mid-ranked individuals had lower energy intake rates in trees with higher amounts of aggression, while energy intake rate of high-ranked individuals was not affected by the amount of aggression in the feeding tree. Energy intake was not influenced by the sex of the individual when rank was held constant statistically. Energy intake was positively correlated with total crown energy (measured in kilojoules) within the feeding tree for two of three study groups. This difference may be explained by the quality of each group’s territory. Finally, high-ranked individuals are responsible for the majority of agonism within feeding trees and target middle- and low-ranked individuals equally. These findings fit the predictions of current socioecological models for within-group contest competition over food resources. The results of this study suggest that within-group competition affects energy intake rate in white-faced capuchin monkeys.