Search

In May and June 2024, a die-off of Mexican mantled howler monkeys (Alouatta palliata mexicana) occurred in southern Mexico. This commentary documents the event, attributing it to extreme heatwaves, drought, wildfires, and habitat impoverishment. Despite their reported resilience to habitat disturbances, mantled howler monkey mortality rate in some areas reached 31%. Key evidence points to heatstroke as the primary cause of death, exacerbated by limited hydration and reduced dietary diversity in disturbed habitats. Immediate responses included community-led rescues (e.g., hydrating the monkeys), coordination of rescue activities by nongovernmental organizations (NGOs) (e.g., managing donations), involvement of scientists (e.g., monitoring of primate populations), and assistance from government officials (e.g., providing legal support for animal management). This event underscores the urgency of developing action plans to prevent and attend future crises. Among other actions, we highlight (i) establishing primate care infrastructure with medical and rehabilitation centers; (ii) developing protocols and training programs to ensure rapid crisis response; (iii) fostering collaboration among government, NGOs, and academic institutions for effective crisis management; and (iv) developing targeted research on climate change impacts, predictive models, and long-term health monitoring. We emphasize the critical need for coordinated conservation efforts to protect wild primates and maintain natural ecosystem resilience in the face of escalating climate challenges., (© 2024 Wiley Periodicals LLC.)

Among mammals, the order Primates is exceptional in having a high taxonomic richness in which the taxa are arboreal, semiterrestrial, or terrestrial. Although habitual terrestriality is pervasive among the apes and African and Asian monkeys (catarrhines), it is largely absent among monkeys of the Americas (platyrrhines), as well as galagos, lemurs, and lorises (strepsirrhines), which are mostly arboreal. Numerous ecological drivers and species-specific factors are suggested to set the conditions for an evolutionary shift from arboreality to terrestriality, and current environmental conditions may provide analogous scenarios to those transitional periods. Therefore, we investigated predominantly arboreal, diurnal primate genera from the Americas and Madagascar that lack fully terrestrial taxa, to determine whether ecological drivers (habitat canopy cover, predation risk, maximum temperature, precipitation, primate species richness, human population density, and distance to roads) or species-specific traits (body mass, group size, and degree of frugivory) associate with increased terrestriality. We collated 150,961 observation hours across 2,227 months from 47 species at 20 sites in Madagascar and 48 sites in the Americas. Multiple factors were associated with ground use in these otherwise arboreal species, including increased temperature, a decrease in canopy cover, a dietary shift away from frugivory, and larger group size. These factors mostly explain intraspecific differences in terrestriality. As humanity modifies habitats and causes climate change, our results suggest that species already inhabiting hot, sparsely canopied sites, and exhibiting more generalized diets, are more likely to shift toward greater ground use.

Recent work suggests that collective computation of social structure can minimize uncertainty about the social and physical environment, facilitating adaptation. We explore these ideas by studying how fission-fusion social structure arises in spider monkey ( Ateles geoffroyi ) groups, exploring whether monkeys use social knowledge to collectively compute subgroup size distributions adaptive for foraging in variable environments. We assess whether individual decisions to stay in or leave subgroups are conditioned on strategies based on the presence or absence of others. We search for this evidence in a time series of subgroup membership. We find that individuals have multiple strategies, suggesting that the social knowledge of different individuals is important. These stay-leave strategies provide microscopic inputs to a stochastic model of collective computation encoded in a family of circuits. Each circuit represents an hypothesis for how collectives combine strategies to make decisions, and how these produce various subgroup size distributions. By running these circuits forward in simulation we generate new subgroup size distributions and measure how well they match food abundance in the environment using transfer entropies. We find that spider monkeys decide to stay or go using information from multiple individuals and that they can collectively compute a distribution of subgroup size that makes efficient use of ephemeral sources of nutrition. We are able to artificially tune circuits with subgroup size distributions that are a better fit to the environment than the observed. This suggests that a combination of measurement error, constraint, and adaptive lag are diminishing the power of collective computation in this system. These results are relevant for a more general understanding of the emergence of ordered states in multi-scale social systems with adaptive properties-both natural and engineered., (Copyright © 2020 Ramos-Fernandez, Smith Aguilar, Krakauer and Flack.)

Some social species exhibit high levels of fission-fusion dynamics (FFD) that improve foraging efficiency. In this study, we shed light on the way that FFD allows animal groups to cope with fluctuations in fruit availability. We explore the relative contribution of fruit availability and social factors like sex in determining association and proximity patterns in spider monkeys. We tested the influence of fruit availability and social factors on the association and proximity patterns using three-year data from a group of spider monkeys in the Yucatan Peninsula of Mexico. We identified subgroup members and estimated their Interindividual distances through instantaneous scan sampling. We evaluated fruit availability by monitoring the phenology of the 10 most important food tree species for spider monkeys in the study site. Social network analyses allowed us to evaluate association and proximity patterns in subgroups. We showed that association patterns vary between seasons, respond to changes in fruit availability, and are influenced by the sex of individuals, likely reflecting biological and behavioral differences between sexes and the interplay between ecological and social factors. In contrast, proximity patterns were minimally affected by changes in fruit availability, suggesting that social factors are more important than food availability in determining cohesion within subgroups., (© 2019 Wiley Periodicals, Inc.)

Network analysis has increasingly expanded our understanding of social structure in primates and other animal species. However, most studies use networks representing only one interaction type, when social relationships (and the emerging social structure) are the result of many types of interactions and their interplay through time. The recent development of tools facilitating the integrated analysis of multiple interaction types using multiplex networks has opened the possibility of extending the insight provided by social network analysis. We use a multiplex representation of interactions among the members of a group of wild Geoffroy's spider monkeys (Ateles geoffroyi), to study their social structure. We constructed a six-layered multiplex network based on three indices of overt social interactions (aggression, embraces, grooming) and three distance-based indices (contact, proximity, and association). With tools provided by the MuxViz software, we assessed the relevance of including all six indices in our analysis, the role of individuals in the network (through node versatility), and the presence of modules and non-random triadic structures or motifs. The multiplex provided information which was not equivalent to any individual layer or to the simple aggregation of layers. Network patterns based on associations did not correspond with those observed for overt-interactions or for the multiplex structure. Males were the most versatile individuals, while multiplex modularity and motifs highlighted the relevance of different interaction types for the overall connectivity of the network. We conclude that the multiplex approach improves on previous methods by retaining valuable information from each interaction type and how it is patterned among individuals.

We report 2 cases of predation on an adult and a subadult spider monkey (Ateles geoffroyi) by a puma (Puma concolor) and an unidentified terrestrial predator at the natural protected area of Otoch Ma'ax yetel Kooh, in the Yucatan Peninsula, Mexico. Although spider monkeys are believed to experience overall low predation pressure compared to other primate species, our observations show that predation occurs in the study area and therefore behavioral strategies are likely to be in place to reduce predation risk. Our observations are further evidence that terrestrial predators are a threat for both young and full-grown spider monkeys., (© 2018 S. Karger AG, Basel.)

Ecological and social factors influence individual movement and group membership decisions, which ultimately determine how animal groups adjust their behavior in spatially and temporally heterogeneous environments. The mechanisms behind these behavioral adjustments can be better understood by studying the relationship between association and space use patterns of groups and how these change over time. We examined the socio-spatial patterns of adult individuals in a free-ranging group of spider monkeys (Ateles geoffroyi), a species with high fission-fusion dynamics. Data comprised 4916 subgroup scans collected during 325 days throughout a 20-month period and was used to evaluate changes from fruit-scarce to fruit-abundant periods in individual core-area size, subgroup size and two types of association measures: spatial (core-area overlap) and spatio-temporal (occurrence in the same subgroup) associations. We developed a 3-level analysis framework to distinguish passive associations, where individuals are mostly brought together by resources of common interest, from active association, where individuals actively seek or avoid certain others. Results indicated a more concentrated use of space, increased individual gregariousness and higher spatio-temporal association rates in the fruit-abundant seasons, as is compatible with an increase in passive associations. Nevertheless, results also suggested active associations in all the periods analyzed, although associations differed across seasons. In particular, females seem to actively avoid males, perhaps prompted by an increased probability of random encounters among individuals, resulting from the contraction of individual core areas. Our framework proved useful in investigating the interplay between ecological and social constraints and how these constraints can influence individual ranging and grouping decisions in spider monkeys, and possibly other species with high fission-fusion dynamics.

Animal home ranges may vary little in their size and location in the short term but nevertheless show more variability in the long term. We evaluated the degree of site fidelity of two groups of spider monkeys (Ateles geoffroyi) over a 10- and 13-year period, respectively, in the northeastern Yucatan peninsula, Mexico. We used the Local Convex Hull method to estimate yearly home ranges and core areas (defined as the 60% probability contour) for the two groups. Home ranges varied from 7.7 to 49.6 ha and core areas varied from 3.1 to 9.2 ha. We evaluated the degree of site fidelity by quantifying the number of years in which different areas were used as either home ranges or core areas. Large tracts were used only as home ranges and only for a few years, whereas small areas were used as either core area or home range for the duration of the study. The sum of the yearly core areas coincided partially with the yearly home ranges, indicating that home ranges contain areas used intermittently. Home ranges, and especially core areas, contained a higher proportion of mature forest than the larger study site as a whole. Across years and only in one group, the size of core areas was positively correlated with the proportion of adult males in the group, while the size of home ranges was positively correlated with both the proportion of males and the number of tree species included in the diet. Our findings suggest that spider monkey home ranges are the result of a combination of long-term site fidelity and year-to-year use variation to enable exploration of new resources.