Drivers of food-related agonism among urban capuchin monkeys, Sapajus libidinosus (Primates: Cebidae)

ABSTRACT

The capacity of a primate to evaluate the energy concentration of a resource is a key aspect of its evolutionary fitness. In primate groups, factors such as resource distribution and energy content influence competition for limited food. The availability of high-energy anthropogenic food sources in urban environments can increase aggression and impact social interactions among animals, particularly influencing female reproductive success. Based on this theoretical framework, we conducted an experiment on free-ranging tufted capuchins, Sapajus libidinosus (Spix, 1823), in an urban forest fragment in the city of Goiânia, Central Brazil. We manipulated the energy concentrations of 17 food types to test the relationship between resource value and the frequency of disputes over food access. We conducted 49 experimental sessions and used Generalized Linear Models (GLM) and Structural Equation Modeling (SEM) to analyze the relationships among environmental variables, food quality variables, and dispute frequency. Our results indicate that the energy content of the food resource was indirectly linked to the frequency of disputes, and this relationship was mediated by the number of females per experimental session. While the number of males per experimental session was more strongly related to the overall frequency of disputes, the number of females per experimental session was specifically associated with the energetic value of the food. Further studies are required to determine whether competition for specific nutrients is more important than overall energy content.

KEYWORDS
Aggression; contest competition; diet quality; disputes; foraging strategies; metabolizable energy

INTRODUCTION

When food resources are limited, competition for food is inevitable among members of the same primate group, as they are the primary competitors for available sustenance (Koenig 2002, Shultz and Dunbar 2022). Under favorable conditions, certain animals exhibit resource defense, hereafter referred to as disputes, in which dominant individuals actively guard the food resource (Fischer et al. 2023, Fouilloux et al. 2023). Disputes can manifest as aggressive threats, displacement, or physical attacks (Westergaard et al. 2003, Vogel and Janson 2007). Contest competition is more common when resource items are aggregated and easily monopolized (i.e., medium-sized and clustered in time and space; Hirsch 2007). In such cases, dominant individuals often use disputes to restrict subordinates’ access to resources (Holekamp and Strauss 2016).

A critical factor influencing the likelihood of disputes over resources is their value (Georgiev et al. 2013). Numerous studies have demonstrated that access to high-energy food is directly linked to reproductive output and competitive success across a wide range of species, including humans (Međedović and Bulut 2019); bears, Ursus arctos Linnaeus, 1758 (Skuban et al. 2016); chimpanzees, Pan troglodytes (Blumenbach, 1775) (Houle and Wrangham 2021); orangu­tans, Pongo pygmaeus (Linnaeus, 1760) (Knott et al. 2008); and hyenas, Crocuta Crocuta (Erxleben, 1777) (Mann et al. 2018). Individuals consuming more calories build greater energy reserves, providing advantages during resource scarcity (Marshall and Wrangham 2007, Hanya and Chapman 2013, Lousa et al. 2022). Increased energy intake also enhances physical strength, agility, and endurance, aiding in outcompeting rivals during hunting or foraging and thereby conferring fitness advantages (Kooijman 1986, Hubel et al. 2016). Within social groups, dominance hierarchies often emerge, with higher-ranking individuals gaining preferential access to resources (Janson and van Schaik 1988, Vogel 2005, Holekamp and Strauss 2016). An animal’s ability to compete for and maintain dominance is also influenced by caloric intake. Well-nourished individuals tend to be physically fit, assertive, and competitive, which allows them to attain and maintain dominant positions and to reproduce more frequently (Hirsch 2007, Stockley and Bro-Jørgensen 2011).

Males with access to high-energy food resources can allocate more energy to courtship displays, territorial defense, or physical competition, enhancing their chances of securing mates (Higham et al. 2011, Clutton-Brock and Huchard 2013a). However, the energetic content of food is particularly crucial for female primates (van Schaik 1996, Sterck et al. 1997, Stockley and Bro-Jørgensen 2011, Hare and Simmons 2019, Patterson et al. 2021). Female primates expend significantly more energy than males during parental investment, including gestation, lactation, and parental care (Stockley and Bro-Jørgensen 2011). Access to greater caloric intake enables females to invest more energy in reproduction, thereby providing their offspring with a competitive advantage (Verderane et al. 2013). Consequently, female fitness is constrained by the amount of energy they can obtain from their environment (Koenig 2002, Rosvall 2011, Stockley and Bro-Jørgensen 2011, Verderane et al. 2013).

In general, foods with higher energy content would be associated with a higher frequency of disputes compared to foods with lower energy content. This is because the potential reward for winning a dispute, i.e., greater energy intake, outweighs the energy expended in the conflict (Brown 1964) and can be invested more heavily in reproduction. High-energy foods would attract more individuals, prolong feeding time, and consequently increase opportunities for aggression (Vogel and Janson 2007, Heesen et al. 2014).

Urban environments offer food sources that are more appealing, digestible, and energy-rich than their natural counterparts. These foods typically contain high levels of simple carbohydrates, saturated fats, and proteins (Milton 1999). Human activities often create predictable food sources in terms of location and timing (Lousa et al. 2022, Lousa and Mendes 2024), leading to increased aggression over anthropogenic food compared to natural alternatives (Lousa and Mendes 2022, Lousa et al. 2024). Moreover, the consistent availability of urban food, often replenished at irregular intervals (Shochat et al. 2006), can serve as a reliable resource for animals during periods of natural food scarcity (Sha and Hanya 2013). However, these food sources can also pose health risks for primates (Back and Bicca-Marques 2025), including plastic ingestion (Lousa et al. 2022) and alterations to the gut microbiota (Amato et al. 2025).

Previous research has not consistently established a correlation between a resource’s energy content-measured as Crown Energy in tree fruit biomass × kJ/fruit-and the frequency of disputes (Vogel and Janson 2007, Back and Bicca-Marques 2019). However, some studies have observed a trend toward increased dispute frequency when individuals consume higher-energy foods (e.g., fruit versus flowers), even without precise energy measurements (Su and Birky 2007, Wheeler et al. 2013, Wright and Robbins 2014, González et al. 2018). It is important to note that these observational studies did not control for variations in feeding patch size, food presentation methods, or the nutritional and energetic quality of the food.

The opportunity for disputes-defined by feeding time and the number of individuals present-has emerged as the primary predictor of dispute frequency at food sources (Vogel and Janson 2007, Heesen et al. 2014). Ano­ther factor identified as a cause of disputes is that when individuals are highly clustered, they are in closer proximity to potential interaction partners, thereby increasing the likelihood of aggression (Seex et al. 2022). Nevertheless, these studies overlooked the potential influence of food energy content on dispute opportunities. High-energy foods might attract more individuals, extending feeding time and indirectly increasing the likelihood of disputes.

Unlike previous research (Vogel and Janson 2007, Heesen et al. 2014), this study employs a field experiment. Field experiments are an ideal approach for addressing this type of question in primatology because they combine the experimental control of variable manipulation with the ecological validity of natural settings (Janson 2012), thereby avoiding the artificiality of laboratory conditions.

This study investigated two groups of capuchin monkeys, Sapajus libidinosus (Spix, 1823), inhabiting an urban park in the city of Goiânia, Central Brazil. These animals are characterized by sexual dimorphism (Fragaszy et al. 2016), and dominant males are typically dominant over adult females (Lousa et al. 2022). Males may exchange access to food resources with females in return for copulations and grooming (Verderane et al. 2013).

We investigated the relationship between the energy content of food items (kcal/100 g of edible food) and the frequency of disputes during experimental sessions. Specifically, we aimed to determine whether this relationship is direct or mediated by other factors, such as the number of individuals present or feeding time. To this end, feeding experiments were conducted using several food items on a feeding platform. We also considered additional factors that may influence disputes, including individual food consumption, feeding context (e.g., activity on the platform and surrounding area), and number of individuals feeding. Our primary prediction was that higher energy content would be positively correlated with an increased frequency of disputes (Prediction 1).

We would expect a positive relationship between reduced interindividual spacing during foraging (i.e., a higher frequency of simultaneous feeding or a lower mean frequency of occupied quadrants) and the number of disputes observed during a given session, based on the premise that increased opportunities for interaction lead to a higher incidence of disputes (Vogel and Janson 2007; Prediction 2). Similarly, we would expect an increase in the opportunity for disputes when feeding time increases (Vogel and Janson 2007, Chancellor and Isbell 2009, Wright and Robbins 2014, Grueter et al. 2016; Prediction 3). The number of disputes observed during experimental sessions would positively correlate with the mean number of adult males and females recorded, as disputes are typically the behavioral strategy adults use to gain access to food resources (Clutton-Brock and Huchard 2013b; Predictions 4 and 5).

We also examined whether variables such as the number of individuals present, their spatial distribution, or the total feeding time on the experimental food might mediate the relationship between caloric content and dispute frequency (Prediction 6). A summary of the study’s predictions can be found in Table 1 and Table S1.

Table 1
Initial predictions of relationships between the focal dependent variable and the six independent variables of the tested models.

Prediction	Dependent variable	Independent variable	Predicted relationship
1	Number of disputes	Caloric content	Positive
2	Number of disputes	Individuals feeding together on the feeding platform	Positive
3	Number of disputes	Time spent feeding	Positive
4	Number of disputes	Mean Adult Males per scan	Positive
5	Number of disputes	Mean Adult Females per scan	Positive
6	Number of disputes	Caloric content	Mediation

MATERIAL AND METHODS

Study site and population

The study was conducted in Bosque Bougainville Padre Cesário Galvão, a 9-ha forested municipal park located in Goiânia, Goiás State, central Brazil (-16.722443°, -49.228041°). The park hosts a resident population of S. libidinosus, which have frequent access to both human-provided food and discarded waste left by residents. A neighbor living adjacent to the park regularly supplied between two and three dozen bananas on a platform near the fence at predictable times, despite being advised by authorities and researchers not to feed the monkeys. Additionally, on a platform located deeper within the forest, staff from the Goiânia Environmental Agency (AMMA-Goiânia) provided the monkeys with assorted fruits and vegetables weekly, on varying days. The population consisted of 31 to 35 capuchins, organized into two stable social groups: the Dom Pedro group, composed of two adult males (one of which disappeared at the beginning of the study), eight adult females, and ten immatures; and the Cicatriz group, composed of three adult males, four adult females, and six immatures. All individuals were individually identified. For a more detailed description of the study groups and study site, see Lousa and Mendes (2022).

Experimental design

A 62-centimeter-diameter circular wooden platform (repurposed construction spool originally used for winding electrical cables) was secured to a 30-centimeter-high support. A black, concave feeding tray (60 cm in diameter) was fastened to the center of the platform with a screw (Fig. 1). The platform was positioned in a small clearing located 10 m from the forest edge, but still within the forest. Based on Janson’s (1996) observation that dominant individuals can control food access within a 10-meter radius for S. nigritus, we defined a 15.31-meter-radius experimental area centered on the platform to ensure that the entire setup functioned as a single food patch (Fig. 2A). Within this area, a few tall trees were present, although most of the vegetation consisted of shrubs. A Sony DCR-SR45 video camera was placed 5 m from the platform, at position B (Fig. 2B). The quadrants were numbered 1-4 to facilitate mapping the distribution of individuals within the experimental area.

Figure 1
The experimental feeding platform used in the present study: (A) lateral view showing the complete platform, 62 cm in diameter and 30 cm in height; (B) close-up of the black-painted, concave feeding tray (60 cm in diameter) containing chopped avocado.

Figure 2
Experimental design. A) A 15m radius from the platform edge defined the experimental area; B) the video camera was placed 5 m from the platform edge, between quadrants 2 and 3.

Capuchins were provided with 17 different food items selected based on variations in their carbohydrate (1.16-79.40 g/100 g edible portion) and lipid (0.21-62.4 g/100 g edible portion) content (TBCA 2023). Caloric values also varied significantly among the food items (Table 2, Table S2). To standardize food consistency, edible portions were processed in a blender, ensuring uniformity between seeds (e.g., oats) and larger pieces (e.g., avocado; Fig. 1B).

Table 2
Calorie content and experimental characteristics of each food item. Data obtained from TBCA (2023) unless otherwise stated.

Food	Kcal per 100 g	Mean amounts consumed (g)	Number of experimental sessions
Carrot	31	465	2
Avocado	76	230	3
Mango	77	465	3
Banana	109	483	3
Quail egg	157	487	3
Cassava	184	489	3
Apricot	254	214	3
Dried fig	257	500	3
White rice	346	53	3
Cornmeal	354	128	3
Oats	370	383	3
Coconut meat	423	479	3
Grated coconut *	501	242	3
Cashew nut	582	292	3
Almond	632	416	3
Sunflower seed	639	277	3
Hazelnut	673	303	2
Total/Mean	333	347.41	49

• *USDA (2012).

Procedures

Behavioral data were collected over 49 days between March 2009 and September 2010. Food introduction followed a two-stage process: a preliminary stage and a subsequent experimental session. In the preliminary stage, on the day preceding each experimental session, 100 g of the target food were placed on the platform to mitigate neophobia.

Two observers conducted the experimental sessions, which began with placing 500 g of the target food on the platform at 8:00 a.m. Observations started when at least two individuals were within the experimental area and one was interacting with the platform. Scan sampling (Altmann 1974) was employed, consisting of 30-second observations separated by one-minute intervals. Data collected during each scan included an individual’s location within the experimental area (platform, 0-5 m, 5-10 m, or 10-15 m from the edge of the platform), quadrant (1-4), and feeding activity (consuming experimental food or other items). Each individual was categorized into one of 13 spatial categories (Fig. 2). Sessions concluded when all food was consumed or when the last individual moved beyond five meters from the platform (Fig. 2B).

In addition to scan sampling, a second observer employed all-occurrences sampling (Altmann 1974) to record disputes during each experimental session. For each dispute, they noted the initiator and target individuals. Video footage from the camera monitoring the feeding platform supplemented these observations. When food remained on the platform, it was weighed to determine the quantity consumed.

Study parameters

With one exception (Table 1), the caloric content of the food items used in this study was obtained from TBCA (2023). All caloric values were reported in kilocalories per 100 grams of edible portion. Only the edible portions of the food were presented on the platform (e.g., peeled bananas and mangos).

Disputes were defined based on three types of behavior: threats, displacements, and physical attacks. These behaviors were defined as follows: (i) threats - an indivi­dual directs agonistic postures or vocalizations toward one or more conspecifics without making physical contact; (ii) displacements - an individual approaches another, which immediately moves away, allowing the approaching indivi­dual to take its place (the approaching individual does not display overt aggression); and (iii) physical attacks - an individual advances toward one or more others and makes physical contact, such as forcefully pushing or biting. Each dispute was defined and scored as a single behavioral episode, from the initiation of the behavior to its conclusion (e.g., from the onset of a threat display, such as a capuchin monkey showing its teeth, until the individuals separated). The frequency of subcomponents (e.g., the number of times teeth were shown) was not counted within a single dispute, as the dispute itself represents the unit of analysis. We recorded the sex and age of the first individual to initiate the aggressive behavior and of the first individual to receive it, excluding cases in which additional individuals joined the interaction after the aggression had already begun.

The spatial distribution of competitors within the experimental area was assessed using two metrics: (i) mean frequency of quadrants - the total number of quadrants utilized by individuals divided by the experiment duration (indicative of group dispersion during foraging; fewer quadrants suggest closer proximity); and (ii) frequency of simultaneous feeding - the proportion of scan samples in which two or more individuals fed together on the platform (reflecting the potential for disputes due to increased individual overlap).

Capuchin participation in each experimental session was estimated by summing the mean number of observed adult females and adult males in scan samples. We also determined the number of different individuals that appeared during each experiment.

The total feeding time per experimental session was calculated based on scan samples in which at least one individual was observed consuming experimental food. Feeding time was considered continuous unless interrupted by more than three consecutive scan samples without feeding activity.

Data analysis

We analyzed the data in the R statistical environment (R Core Team 2024). To test which variables are associated with the frequency of agonistic disputes, we fitted a Gene­ralized Linear Model (GLM) with a negative binomial distribution and a log link function. We did not standardize dispute counts by total feeding time or include feeding time as an offset because dispute frequency showed a nonlinear relationship with total feeding time per session. For this reason, total feeding time was included as an independent predictor rather than as an offset term. The final model, implemented using the MASS package (Venables and Ripley 2002), included the following predictors: (i) feeding group size (mean number of adult females and adult males); (ii) competitor distribution (frequency of simultaneous feeding on the platform); (iii) total feeding time; and (iv) caloric content (kcal per 100 g of edible portion).

To investigate whether specific variables mediated the relationship between food caloric content and dispute frequency, we used a Structural Equation Model (SEM), specifically a mediation model. In this context, mediation occurs when the effect of an independent variable (caloric content) on a dependent variable (dispute frequency) is transmitted, in part or entirely, through one or more intermediate variables. The model was estimated using the lavaan package (Rosseel 2012) in R using fixed-effects mediation. We assessed the potential influence of caloric content on dispute frequency, considering mediating variables related to both calorie consumption and the disputes themselves. We tested all variables as potential mediators; the best-fitting model included the mean number of observed adult females and adult males per scan and the mean frequency of quadrants. Direct effects, which represent the independent variable’s influence on the dependent variable without a mediator, were measured through regression analyses. Indirect effects, representing the independent variable’s influence through a mediator, were also determined. The total effect was calculated as the sum of the direct and indirect effects. A bootstrap analysis with 1,000 resamples was conducted to calculate the 95% confidence intervals for the indirect effects. The datasets supporting the conclusions of this article are included in the Table S2.

RESULTS

A total of 145 disputes occurred across 34 of the 49 experimental sessions (mean = 2.96 ± 3.63 disputes/session). These included 105 threats, 26 displacements, and eight physical attacks. Both participants, actor and receiver, were identified in 95 disputes (70 threats, 22 displacements, 3 attacks; Table 3). On average, 371.72 grams of food (range: 2-500 g) were consumed per session, with a mean total feeding time of 40.02 ± 25.78 minutes per experimental session.

Table 3
Sex-age distribution of the different types of agonistic behavior (displacements, threats, and physical attacks) observed in the disputes recorded in the experiment between dyads in which both participants were identified individually. The actors are in the row; the recipients are in the column. Juvenile sex could not be determined.

	Adult Female	Adult Male	Juvenile	Total	Events per individual†
Displacements
Adult Female	7	0	5	12	0.92
Adult Male	1	2	5	8	2.25
Juvenile	1	0	3	4	0.38
Total	9	2	13	26†	0.87
Threats
Adult Female	15	7	10	32	3.31
Adult Male	7	3	13	23	9.75
Juvenile	5	2	3	10	1.00
Total	27	12	26	105‡	3.50
Physical attacks
Adult Female	0	0	1	1	0.08
Adult Male	0	0	1	1	1.00
Juvenile	1	0	0	1	0.23
Total	1	0	2	8₣	0.27

• †4 disputes with unidentified individuals; ‡37 disputes with unidentified individuals ₣5 disputes with unidentified individuals. †Events per individual refer to total occurrence of dispute events modeled by the quantity of individuals in each sex-age category here, i.e., total occurrences of disputes by sex-age category/total individuals by sex-age category.

Although more disputes involved adult females in absolute terms, especially displacements and threats (Table 3), adult males exhibited a disproportionately higher per-individual involvement in aggressive interactions.

Disputes

The best-fitting model (AIC = 192.52) for predicting dispute frequency included the following predictors: frequency of simultaneous feeding, feeding duration, and mean number of adult males and adult females per scan. The caloric value of the food was not included in the selected model (Table 4). Variance Inflation Factor (VIF) values were below 2, indicating no collinearity among predictors (Table S3).

Table 4
Summary of the Generalized Linear Model (GLM) for the Frequency of Disputes.

Variable	Beta	SE	Z Value	P Value
Simultaneous feeding	0.065	0.215	3.018	0.002
Duration	0.015	0.004	3.808	<0.001
Adult Male	0.726	0.304	2.384	0.017
Adult Female	0.611	0.227	2.692	0.007

Disputes vs. food caloric content

The total effect of food caloric content on dispute frequency was statistically significant (Z = 2.67; β = 0.007, p = 0.018). However, the direct effect was not significant (Z = 1.098; β = 0.003, p = 0.272).

The indirect effect through the mean number of adult females per scan was significant (Z= 2.027; β = 0.002, p = 0.043; Figs 3-5). In contrast, neither the mean frequency of quadrants (Z = 1.230; β = 0.002, p = 0.219) nor the mean number of adult males per scan (Z = 0.517; β = 0.001, p = 0.605) were significant mediators. This finding indicates that the mean number of adult females per scan significantly mediates the relationship between food caloric content and dispute frequency. Combined, all variables explained 64% of the variance in dispute frequency (Figs 3, Figs S1, S2). The variables exhibited low correlations with no indication of multicollinearity, and the model showed a good fit (χ² = 5.237, df = 3, p = 0.155; Fig. S3).

Figure 3
Direct effects between the variables examined in the model.

Figures 4-5
Effects of kcal on the number of females (4) and of the number of females on disputes (5).

DISCUSSION

In this experiment, we tested whether there was a relationship between food energy content (caloric value) and the frequency of disputes, or whether other variables were more influential, as suggested by previous studies (Vogel and Janson 2007, Heesen et al. 2014), such as opportunities for disputes and the aggregation of individuals at the food source. To address this question, we conducted an experiment that controlled the quantity and presentation of food on a feeding platform for urban capuchin monkeys. Our findings indicate that food caloric content predicted the number of females present, which in turn mediated the frequency of disputes.

There was no direct relationship between caloric content and the frequency of disputes during the experimental sessions, which does not support Prediction 1 (Tables 1, 5 and Table S1 summarize the study predictions). Our findings are consistent with previous primate studies (Vogel and Janson 2007, Heesen et al. 2014, Wheeler et al. 2013, Grueter et al. 2016), which also failed to establish a consistent relationship between energy availability and dispute frequency. An increase in the frequency of simultaneous feeding on the platform was associated with a higher frequency of disputes, corroborating Prediction 2. Our observations revealed a clear pattern of platform use: dominant individuals typically monopolized the feeding area, whereas subordinate individuals made brief, rapid visits to obtain food before retreating to avoid competition. Dominant monkeys frequently excluded subordinates from the platform and consequently consumed larger quantities of food directly on it. Subordinates foraged by quickly approaching the platform to seize food and then immediately retreating to consume it elsewhere. Disputes often occurred when subordinates attempted to gain access to the platform, suggesting that spatial dynamics and competitive exclusion around the feeding site were central drivers of aggression.

Table 5
Conclusions of the predictions and whether they were corroborated.

Prediction	Conclusion	Supported
1	An increase in calories does not directly lead to an increase in disputes.	No
2	An increase in the frequency of simultaneous feeding on the platform led to an increase in disputes.	Yes
3	An increase in feeding duration led to an increase in disputes.	Yes
4	An increase in the number of adult males led to an increase in disputes.	Yes
5	An increase in the number of adult females led to an increase in disputes.	Yes
6	The relationship between caloric content and disputes was mediated by the number of adult females.	Yes

An increase in feeding duration led to an increase in the frequency of disputes, supporting Prediction 3. As feeding time increases, the statistical probability of dispute occurrence also increases (Vogel and Janson 2007, Janson and Vogel 2006, Chancellor and Isbell 2009, Heesen et al. 2014; Table S4). However, this increase in disputes did not appear to be proportional to total feeding duration. Instead, disputes occurred more frequently at the beginning of the experimental sessions, when individuals were likely less satiated (Janson and Vogel 2006, Grant et al. 2002) and when more individuals were present at the food source.

The mean number of adult males and adult females within the experimental area was positively related to the frequency of disputes, supporting Predictions 4 and 5. Consistent with the findings of Vogel and Janson (2007) and Heesen et al. (2014), our data showed that only the number of adults influenced dispute frequency (Creel et al. 2013). Our results indicated a stronger effect of males: the presence of one additional male per scan increased the number of disputes by 106% (with other variables held constant), whereas the presence of one additional female per scan increased disputes by 84%.

Although the number of adult males had a greater impact on dispute frequency, the number of females mediated the relationship between food energy content and dispute frequency, supporting Prediction 6. The presence of adult males in the experimental area increased disputes independently of food energy content, suggesting that males may not necessarily be competing directly for the food resource itself (Clutton-Brock and Huchard 2013b).

Higher-quality food sources attracted more adult females, who then competed more intensely for these resources. In other words, adult females were drawn to foods with higher caloric value, resulting in increased aggression. This pattern indicates that females were competing for high-energy foods, as also reported by Pusey and Schroepfer-Walker (2013), given that their reproductive success is often constrained by the energetic value of their diet (Clutton-Brock and Huchard 2013a).

Our results are particularly applicable to urban parks. Anthropogenic foods, such as provisioned items and garbage, are more abundant in these areas (Lousa et al. 2022) and, like our experimental platform, tend to be more energy-rich (Milton 1999) and spatially clumped (Lousa and Mendes 2022, Lousa et al. 2024), likely increasing aggressive interactions (i.e., disputes) among primates, especially adults.

Understanding the relationship between food energy content and aggression offers insights into the complex dynamics of resource availability, competition, and primate social behavior. Our results show that caloric content influenced the number of females present, which in turn mediated the frequency of disputes. Consistent with previous research, contest competition was primarily driven by the number of adult competitors rather than by resource quality.

It is possible that individuals compete for specific nutrients rather than total energy (Righini 2017). If this is the case, competitive interactions may vary idiosyncratically among individuals rather than following a universal pattern. Investigating this hypothesis would require detailed monitoring of individual feeding behavior, which was beyond the scope of this study.

Another limitation concerns the relatively small number of experimental sessions, as it was not feasible to provide large quantities of food to the monkeys, resulting in only a few sessions per month. Additional research is needed to clarify the mechanisms linking energetic content, resource competition, and aggressive interactions across different primate species.

Data Availability Statement

All data generated and/or analyzed are included in this article and its Supplementary Materials.

Supplementary Materials

Table S1

Predictions of relationships between dependent and independent variables of the tested models and whether the predictions were corroborated. Data type: Predictions.

Table S2

Table used in analyses. Data type: Database.

Table S3

Variance Inflation Factor (VIF) values for each of the independent variables in the model Data type: VIF values.

Table S4

Proportion of agonistic disputes occurring in each third of the experimental sessions, showing a decline in dispute frequency over time. Data type: Proportion data.

Figure S1

Regression lines illustrating the effect of caloric content (kcal) on the mean number of adult females, adult males, and the mean frequency of quadrants. Data type: Regression lines

Figure S2

Linear regressions depicting the effect of the mean number of adult females, adult males, and qua­drants on dispute frequency. Data type: Statistical data

Figure S3

Scatterplot and correlation matrix of independent variables. The diagonal panels display the histograms and density curves illustrating the distribution of each variable (Quadrant, Male, Female). The upper right panels present the linear correlation coefficients (Pearson’s r) between the variable pairs. The lower left panels exhibit the scatterplots, along with a non-parametric smoothing line (red curve) to visualize the pattern of the relationship between the variable pairs. Correlation coefficients close to zero indicate low intercorrelation among the variables, confirming the absence of multicollinearity. Data type: Scatterplot and correlation matrix.

Author: Lousa TC.

Copyright notice: This dataset is made available under the Open Database License - ODBbL (https://opendatacommons.org/licenses/odbl/1.0/). The ODbL is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.

Link: https://doi.org/10.1590/S1984-4689.v43.e25097

ACKNOWLEDGMENTS

We thank Patrícia Izar for assistance with experimental design; Thallita de Grande and Priscylla Amora for field assistance; the Agência Municipal do Meio Ambiente (AMMA) for research authorization; and two anonymous reviewers for constructive comments. We also thank Universidade de Brasília (UnB) and Pontifícia Universidade Católica de Goiás (PUC-GO) for institutional support.

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• https://zoobank.org/A475C277-6DDF-4203-A0B6-308FC955DD6F
• Funding Statement
  This study was financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES Finance Code 001).
• Ethical Statement
  Ethical committee approval was not legally required for these procedures at the time the fieldwork was conducted (2009-2010). Fieldwork was carried out under authorization from the Municipal Environmental Agency of Goiânia (AMMA, permit 2539000/2008).
• AI Statement
  Artificial intelligence tools were used solely to assist with language editing and grammar.
• How to cite this article
  Lousa TC, Mendes FDC (2026) Drivers of food-related agonism among urban capuchin monkeys, Sapajus libidinosus (Primates: Cebidae). Zoologia 43: e25097. https://doi.org/10.1590/S1984-4689.v43.e25097
• Published by
  Sociedade Brasileira de Zoologia at Scientific Electronic Library Online - https://www.scielo.br/zool

Edited by

• Editorial responsibility:
  Guilherme Garbino

Publication Dates

• Publication in this collection
  07 Sept 2026
• Date of issue
  2026

History

• Received
  13 Oct 2025
• Accepted
  28 Apr 2026