Degree of Frugivory Predicts Rates of Food-Related Agonism and Intragroup Proximity in Wild Gray Woolly Monkeys (Lagothrix lagotricha cana)

Abstract

The main factors influencing feeding competition among members of diurnal primate groups are the distribution, availability, and quality of food resources. Socioecological models predict that temporal availability of preferred resources, such as fruit, can influence intragroup feeding competition, which is expected to affect rates of agonism and intragroup spatial patterns. We evaluated the effects of temporal variation in fruit availability on the degree of frugivory (i.e., the proportion of time spent feeding on fruit in relation to total food consumption) and the effects of fruit availability and degree of frugivory on rates of agonistic interactions, and intragroup proximity in two wild groups of gray woolly monkeys (Lagothrix lagotricha cana) in southwestern Brazilian Amazonia. We recorded 227 agonistic interactions via the all occurrences method and 3549 records of spacing via scan sampling during an 8-mo field study from March to October 2017. We found that fruit availability showed a positive relationship with the woolly monkeys' degree of frugivory, which in turn showed a positive relationship with the rates of agonism. We also found that degree of frugivory positively affected intragroup proximity in periods of lower fruit availability, and that agonistic interactions and proximity covaried positively. Conversely, as the degree of frugivory increased, monkeys exhibited greater interindividual distances and, consequently, lower rates of agonism, consistent with lower levels of feeding competition in periods of higher fruit availability. Therefore, we suggest that intragroup contest competition for fruits is an important cost of group living even for generalized, opportunistic frugivorous primates, such as woolly monkeys.

When partitioning is not an option: Resource availability predicts intraguild interactions in two isolated Amazonian primate assemblages

“…On one hand, the negative tendency between feeding‐related and agonistic‐related interactions with fruit availability when overall fruit production was lower than 5% (Figure S1) suggests that in periods of fruit scarcity, the species may switch their diet to include alternative food resources (e.g., flowers, seeds, and arthropods), broadening their diet niche and reducing the chances for interspecific interactions (e.g., Stevenson et al, 2000; Sushma & Singh, 2006). This behavioral strategy is typically employed by fruit specialists such as woolly and spider monkeys to avoid intraspecific contest competition (e.g., Cavalcante et al, 2021; Symington, 1990). We hypothesize that this behavioral flexibility would also prevent costly interspecific interactions at assemblage and guild level.…”

“…Data on rates of interspecific interactions are reported as mean ± SD throughout the text. Given that the study sites did not differ in fruit availability (Wilcoxon rank sum test, W = 51, p = .970), DBH size of trees monitored for fruit availability (W = 44, p = .829), and rates of interspecific interactions (W = 56, p = .391), we pooled the datasets from both sites (e.g., Cavalcante et al, 2021) to increase sample size and statistical power for subsequent analysis.…”

“…We did not observe any case of affiliative interaction (e.g., grooming, play) between gray woolly monkeys and other primate species. We also used the activity in which gray woolly monkeys were engaged during the occurrence of the interaction to classify interactions into feeding and non‐feeding (i.e., traveling, resting, socializing, and other behaviors) contexts (see Cavalcante et al, 2021 for more details on gray woolly monkey activity patterns). We finally recorded the directionality of agonistic interactions (i.e., aggressor and recipient).…”

“…Home range size can reach up to 1021 ha in gray woolly monkey groups (Peres, 1996). The diet of gray woolly monkeys is mainly composed of fruit (up to 80%), leaves, flowers, arthropods, and small vertebrates (Cavalcante et al, 2021;Peres, 1994).…”

“…Fruits are the most contested resource and an important modulator of gray woolly monkeys' social dynamics (Cavalcante et al, 2021).…”