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Context Line-transect sampling is considered to be a more efficient survey method than point-transect sampling to estimate population densities and abundance of many animal species. Aims In the present study, we tested whether this claim holds true when surveying arboreal fast-moving primate species occurring at low densities, and whether the potential difference in efficiency can be explained by the difference in the size of the survey area between the methods. We further examined the impact of survey effort for point-transect sampling. Methods We conducted line- and point-transect sampling for Geoffroy’s spider monkeys (Ateles geoffroyi) in the same locations and compared the numbers of detected individual monkeys and the probability of their occurrence per survey between the two methods. We further compared the data from point-transect sampling gathered within three different waiting periods. Key results We found a higher probability to detect monkeys and a higher number of monkeys during line-transect sampling than during point-transect sampling, but more spider monkeys were detected at point transects when controlling for the size of the survey area. More monkey detections were made during the first 10 min than during the second and third 10-min periods of point-transect surveys. Conclusions We showed that line-transect sampling is more efficient than point-transect sampling when surveying Geoffroy’s spider monkeys in a flat landscape of tropical forest with homogenous visibility. We discuss factors influencing survey results and recommend 20 min as the maximum waiting time at point transects when surveying arboreal mammals. Implications Our study has provided a quantitative approach to compare efficiency across survey methods for fast-moving arboreal animals that occur at low densities, and supports the use of point-transect sampling in sites where line-transect sampling is not feasible, such as in human-modified landscapes.

Access to sufficient water of suitable quality represents a challenge for achieving several dimensions of sustainable development. Currently, water access is restricted to three of 10 persons globally. In rural areas of Mexico and other low-income countries, coverage could be even less due to the absence of formal supply; thus, rural communities usually perform water management. Surrounding community-based water management, various socio-ecological interactions emerge that determine access to water. Access to water will depend on the obstacles or capacities that arise within the socio-ecological system in which the community is immersed. This work identifies barriers and bridges to water access in a rural environment through mixed methods. The article draws on three case studies in southeastern Mexico by analyzing 90 questionnaires conducted at the household level and three focus groups in parallel with water quality analysis and its relationship with management practices. The barriers and bridges were classified into six water access challenges: (i) access to water in a sufficient quantity, (ii) access to water of adequate quality, (iii) access to water for household crop irrigation, (iv) hygiene and sanitation facilities, (v) collective organization, and (vi) climate variability. The main findings indicate that households' water quantity and quality show deficiencies due to the lack of formal infrastructure and represent a health risk. Water fetching has the highest impact on women and children in poor rural areas, and it is a significant barrier to sustainable development. In contrast, the collective organization proved to be an essential bridge for water access in these communities.

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.

Table S1. Group composition and individual characteristics of spider monkeys (Ateles geoffroyi) in the Otoch Ma'ax Yetel Kooh reserve, Yucatan Peninsula, Mexico. Table S2. Results of each statistical model and Post hoc (Turkey test) comparisons. All assumptions for the GLMM analyses were met (collinearity and overdispersion). Table S3. Post-hoc comparison for the analysis of fission-fusion events vs. call rate. Results of each statistical model and Post hoc (Turkey test) comparisons. All assumptions for the GLMM and GLM analyses were met (collinearity and overdispersion). Table S4. Post-hoc comparison for the analysis of changes in audience composition on call vs. call rate. Results of each statistical model and Post hoc (Turkey test) comparisons. All assumptions for the GLMM and GLM analyses were met (collinearity and overdispersion).

Animal communication has long been thought to be subject to pressures and constraints associated with social relationships. However, our understanding of how the nature and quality of social relationships relates to the use and evolution of communication is limited by a lack of directly comparable methods across multiple levels of analysis. Here, we analysed observational data from 111 wild groups belonging to 26 non-human primate species, to test how vocal communication relates to dominance style (the strictness with which a dominance hierarchy is enforced, ranging from 'despotic' to 'tolerant'). At the individual-level, we found that dominant individuals who were more tolerant vocalized at a higher rate than their despotic counterparts. This indicates that tolerance within a relationship may place pressure on the dominant partner to communicate more during social interactions. At the species-level, however, despotic species exhibited a larger repertoire of hierarchy-related vocalizations than their tolerant counterparts. Findings suggest primate signals are used and evolve in tandem with the nature of interactions that characterize individuals' social relationships. Publisher PDF

Within comparative psychology, the evolution of animal cognition is typically studied either by comparing indirect measures of cognitive abilities (e.g., relative brain size) across many species or by conducting batteries of decision-making experiments among (typically) a few captive species. Here, we propose a third, complementary approach: inferring and comparing cognitive abilities through observational field records of natural information gradients and the associated variation in decision-making outcomes, using the ranging behavior of wild animals. To demonstrate the feasibility of our proposal, we present the results of a global survey assessing the availability of long-term ranging data sets from wild primates and the willingness of primatologists to share such data. We explore three ways in which such ranging data, with or without the associated behavioral and ecological data often collected by primatologists, might be used to infer and compare spatial cognition. Finally, we suggest how ecological complexity may be best incorporated into comparative analyses. Publisher PDF

Unlike animals living in cohesive groups, those in groups with high fission–fusion dynamics can separate temporarily from other group members. While mechanisms underlying collective decisions are not well understood, it is possible that these separations occur by a divergence of interests between individuals. We evaluated the collective foraging decisions made by a group of Geoffroy's spider monkeys, Ateles geoffroyi, in a tropical forest in the Yucatan peninsula, Mexico. We assessed whether each individual's centrality in the social network, years living in the group, age, sex and social relationships affected the collective decisions. We examined two collective dynamics: foraging movements and arrivals to novel food patches, and in the latter, identified knowledgeable and naive individuals. In both dynamics, spider monkeys exhibited partially shared leadership influenced by individual attributes, particularly the centrality in the social network, age and time in the group. These attributes have been associated with ecological knowledge. In arrivals to novel food patches, individuals most likely to have information about food resources (i.e. central individuals and males) had a greater likelihood to be followed, suggesting an influence of social information on the tendency to follow others. Also, we show evidence that social information could accelerate the arrival of naive individuals to these patches. Collective foraging dynamics in our study group seem to arise from local rules that each individual follows when foraging: when a naive individual needs social information to forage, it will follow the individual that is more likely to have this information, i.e. a central individual or a male; otherwise, when it is not possible or necessary to use social information, naive individuals will follow a partner with which they have a strong social relationship. Thus, the interaction between local decision rules and the structure of the social network could drive collective coordination in fission–fusion dynamics.

Population estimates are critical for making informed conservation decisions. However, methods for data collection and analysis of population estimates from wildlife surveys vary, often preventing comparisons between sites or years. In this study we compared population density estimates of spider monkeys, Ateles geoffroyi, derived from four commonly used methods to the actual density estimate based on known individual monkeys and home-range size and corroborated these results with surveys done on unhabituated monkeys in the same area. We recorded perpendicular distances of individual monkeys in the Otoch Ma’ax yetel Kooh Protected Area during two surveys: within the home range of an individually-recognized spider monkey group (survey one) and largely outside of the home range (survey two). We sighted 278 and 76 spider monkeys for a total effort of 93.74 and 42.78 km in surveys one and two, respectively. The actual density estimate was 65.4 individuals/km2 (survey one). This value lies closer to the population density estimate obtained using the Kelker method (58.2 individuals/km2) than conventional distance sampling (CDS; 92.9–93.8 individuals/km2). Density estimates obtained with King and maximum perpendicular distance methods deviated substantially from the actual density. Population density estimates using the Kelker method and CDS differed less in survey two. Population density estimates differed little whether transects were walked slow or fast. We recommend using the Kelker method and CDS to estimate population density with a correction for distance estimation errors. We demonstrate how studies on populations of known size can improve the methods to survey populations of unknown size.

Understanding population responses to landscape structure is critical to improve landscape planning. Yet, large uncertainty remains about how such responses vary among regions with different disturbance intensity. This knowledge is particularly important for forest-specialist species, such as spider monkeys. Assessing the effect of landscape composition and configuration on the abundance and reproductive success of spider monkeys (Ateles geoffroyi) in two fragmented rainforests with different land-use intensity. We calculated the encounter rate (relative abundance) and immature-to-female ratio (reproductive success) of spider monkeys in two Mexican rainforest regions (12 forest patches per region, ~ 1140 h of field observations), and assessed their responses to three landscape predictors (forest cover, matrix functionality, and forest patch density) considering the scale of effect in each region. Spider monkeys showed different responses to landscape structure in each region. Encounter rate increased strongly with matrix functionality in the more disturbed region, and tended to be negatively impacted by patch density in the best-preserved region, but this latter association was weak. Forest cover was positively related to immature-to-female ratio in both regions, but such association was stronger in the best-preserved region. Our findings suggest that forest loss has stronger negative effects on spider monkeys than forest fragmentation, especially in best-preserved rainforests. Matrix composition is relatively more important in more disturbed regions, where monkeys may be pushed to use the matrix more frequently for feeding and/or traveling. Preventing forest loss and improving matrix quality should be a priority for the conservation of this endangered species.

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.

Ecological niche modeling is used to estimate species distributions based on occurrence records and environmental variables, but it seldom includes explicit biotic or historical factors that are important in determining the distribution of species. Expert knowledge can provide additional valuable information regarding ecological or historical attributes of species, but the influence of integrating this information in the modeling process has been poorly explored. Here, we integrated expert knowledge in different stages of the niche modeling process to improve the representation of the actual geographic distributions of Mexican primates (Ateles geoffroyi, Alouatta pigra, and A. palliata mexicana). We designed an elicitation process to acquire information from experts and such information was integrated by an iterative process that consisted of reviews of input data by experts, production of ecological niche models (ENMs), and evaluation of model outputs to provide feedback. We built ENMs using the maximum entropy algorithm along with a dataset of occurrence records gathered from a public source and records provided by the experts. Models without expert knowledge were also built for comparison, and both models, with and without expert knowledge, were evaluated using four validation metrics that provide a measure of accuracy for presence-absence predictions (specificity, sensitivity, kappa, true skill statistic). Integrating expert knowledge to build ENMs produced better results for potential distributions than models without expert knowledge, but a much greater improvement in the transition from potential to realized geographic distributions by reducing overprediction, resulting in better representations of the actual geographic distributions of species. Furthermore, with the combination of niche models and expert knowledge we were able to identify an area of sympatry between A. palliata mexicana and A. pigra. We argue that the inclusion of expert knowledge at different stages in the construction of niche models in an explicit and systematic fashion is a recommended practice as it produces overall positive results for representing realized species distributions.

The ability to collaborate and to share information about ecosystem dynamics and successful management practices is increasingly important in terms of addressing the constant changes and uncertaint...

Se presentan las percepciones sociales acerca del mono araña por parte de habitantes de once comunidades indígenas de las etnias mixe, zoque, zapoteca, mixteca y chinanteca, del noreste de Oaxaca, sur de México. Dichas percepciones son descritas desde el pensamiento de las mujeres y hombres, además de ser analizadas las implicaciones que estas tienen en la conservación de esta especie en peligro de extinción. Se obtuvieron 84 testimonios y entrevistas de hombres y mujeres, y de acuerdo con los datos recabados, en las cinco etnias las percepciones fueron similares: están ligadas al valor ecológico, al valor de uso, al valor asociado al ecoturismo, al temor y a la indiferencia. La percepción de las mujeres se relaciona con su quehacer cotidiano, y ésta difiere entre las mujeres dedicadas sólo al hogar con las que, además, realizan la recolección de algún recurso alimentario en la montaña. En los hombres se definen tres grupos: los que ven en el mono un blanco de caza secundario; aquellos para quienes representa un valor económico por la venta de crías para diversos fines, y aquellos otros que saben de su valor ecológico en las montañas. El mono araña no juega un papel importante en las actividades de los pobladores y en algunos grupos predomina la apreciación negativa. La situación actual de la especie no es alentadora, y si a esto se suma la percepción negativa de los grupos humanos que habitan cerca de ésta, el riesgo de extinción local se hace latente, por lo que es urgente invertir esfuerzos en su recuperación.

Socioecological theory proposes that the flexibility in grouping patterns afforded by fission–fusion dynamics allows animals to cope with spatiotemporal variability in food abundance. We investigate the influence of fruit tree abundance and foraging environment heterogeneity on fission–fusion dynamics in a group of spider monkeys (Ateles geoffroyi) in the Yucatan peninsula, Mexico. We collected 1300 h of behavioral data and 23 samples of biweekly ecological data from August 2009 to July 2010. We measured fission–fusion dynamics through the temporal variation in the size and composition of subgroups, the spatial dispersion within and between subgroups, and the frequency of fissions and fusions. We measured habitat-wide food abundance of preferred species, including two that differ greatly in their relative abundance: Brosimum alicastrum (a hyperabundant resource) and Ficus spp. (a not so abundant resource but often represented by large trees). We evaluated the foraging environment heterogeneity through the variance in the number of trees with fruit between species. Our results show that, although habitat-wide food abundance is important, the availability of key resources strongly influences the spider monkeys’ fission–fusion dynamics. When there was a high abundance of fruit of Brosimum, subgroups tended to be more stable, smaller, and mixed sex, and their members remained close. In contrast, when Brosimum trees with fruit were scarce, females often formed large, more fluid and dispersed subgroups. Foraging environment heterogeneity had a positive effect on within-subgroup spatial dispersion and rates of fission and fusion. The complex relationships we have uncovered suggest that the flexibility afforded by fission–fusion dynamics is an adaptation to highly variable foraging environments.

The fast movement and high degree of fission-fusion dynamics of spider monkeys (Ateles spp.) make them notoriously difficult to survey. We examined which aspects of survey design affect spider monkey sightings along transects in a group of individually recognized spider monkeys (Ateles geoffroyi) in Punta Laguna, Yucatan, Mexico. We calculated the number of monkeys and subgroups sighted per transect walk. Using generalized linear models, we found no effect of the number of observers, transect type (new vs. existing), walking speed, or time of day on individual monkey counts or subgroup counts. Recounting of individuals was relatively rare and occurred when transects were walked relatively slowly. We missed more young than adult monkeys. The group composition based on survey data was similar to the known group composition. Based on our findings we recommend that surveys performed on relatively flat terrain be conducted at speeds similar to or faster than the moving speed of spider monkeys to minimize recounting of individuals and that young:adult female ratios based on survey data be interpreted as conservative indicators of population health. The novel methods presented to determine sources of bias in population estimates are applicable to a wide range of primates that are difficult to survey.

Living in groups brings benefits to many animals, such as a protection against predators and an improved capacity for sensing and making decisions while searching for resources in uncertain environments. A body of studies has shown how collective behaviors within animal groups on the move can be useful for pooling information about the current state of the environment. The effects of interactions on collective motion have been mostly studied in models of agents with no memory. Thus, whether coordinated behaviors can emerge from individuals with memory and different foraging experiences is still poorly understood. By means of an agent based model, we quantify how individual memory and information fluxes can contribute to improving the foraging success of a group in complex environments. In this context, we define collective learning as a coordinated change of behavior within a group resulting from individual experiences and information transfer. We show that an initially scattered population of foragers visiting dispersed resources can gradually achieve cohesion and become selectively localized in space around the most salient resource sites. Coordination is lost when memory or information transfer among individuals is suppressed. The present modelling framework provides predictions for empirical studies of collective learning and could also find applications in swarm robotics and motivate new search algorithms based on reinforcement., Comment: 10 pages, 4 Figures, accepted in J.R.S. Interface

Social network analysis and agent-based modeling are two approaches used to study biological and artificial multi-agent systems. However, so far there is little work integrating these two approache...

Nonhuman primates’ vocal repertoire has shown little plasticity, with immatures producing adult-like acoustic structures. Yet, the use of different call types shows a degree of socially dependent flexibility during development. In several nonhuman primate species, group members exchange contact calls respecting a set of social and temporal rules that may be learned (e.g., overlap avoidance, turn-taking, social selection of interacting partners, and call type matching). Here, we study the use of contact calls in free-living adult and immature (old and young) spider monkeys (Ateles geoffroyi). We focused our study in two contact call types of the species’ repertoire: whinnies and high-whinnies. Our results suggest that individuals in all age classes produced both call types, with immatures producing less frequently the whinny call type. Immature individuals exchanged calls less often than adults, although their contribution increased with age. Conversely, mature individuals regulated their emissions by (1) exchanging more calls with their preferred affiliative partner and (2) matching the call type, while immatures did not. Our results show that contact call usage changes during development and suggest that adult rules might be learned. We argue that call matching is a “conversational rule” that young individuals acquire with apparent call-type-dependent variations during development. Our findings support the idea that social factors influence vocal development in nonhuman primates. We studied the social rules underlying vocal interaction patterns in free-ranging spider monkeys. We found that, while both immature (old and young) and mature individuals were able to produce the two species contact call types, they differed strongly in the way they used them. Matures called more often and exchanged more, while the vocal response rates of immature individuals increased with age. Also, mature individuals exchanged preferentially with their close associates and matched their call types while immatures did not. As in other species, we predict that these exchange patterns serve as a social rule to maintain and strengthen social bonds between individuals. We discuss our findings in light of the probable role of social learning during acquisition of the appropriate context of calling and of the response to others’ calls. These findings support the idea that social influences guide vocal development in nonhuman primates.

Fission-fusion dynamics (FFD) encompass a behavioral strategy present in many animal species that reduces the costs and increases the benefits of group living. In this case study, we investigated how group characteristics (size and composition) and fission rates in spider monkeys varied in space and time with rainfall, fruit availability, and fruit variability in two sites, each presenting different characteristics regarding the distribution and size of food patches and rainfall. Habitat characteristics strongly influenced FFD in spider monkeys, particularly subgroup size and fission rate. Subgroup size varied with fruit availability and its variability, while fission rates varied with rainfall and fruit variability. However, both subgroup size and fission rate varied in opposite ways, depending upon habitat type. Subgroups tended to present stable mixed-sex composition regardless of fruit availability. We conclude that for spider monkeys, FFD are part of a flexible behavioral strategy to cope with a locally fluctuating environment and with different environments within the geographic range of the species. Fission-fusion dynamics (FFD) constitute a form of social organization that allows some species to take advantage of living in groups under different environmental conditions. The relationship between social organization and environmental variables has been well studied, but inconsistencies remain. One potential reason for these inconsistencies may be the focus of most studies on a single habitat type, with few formal comparisons of FFD in the various habitats occupied by a species. We evaluated how habitat characteristics (e.g., food availability and rainfall) affect FFD (assessed through subgroup size, subgroup composition, and fission rate) in spider monkeys (Ateles geoffroyi) in two different habitat types. We found that within a single habitat type, food availability, variability, and rainfall affected subgroup size and fission rate. Crucially, these relationships contrasted sharply, depending on habitat type. Our study shows that FFD are flexible within and across habitats, indicating the importance of considering habitat characteristics when conducting socio-ecological observations. We caution against generalizations based upon single-habitat studies.

Dung beetles are secondary seed dispersers, incidentally moving many of the seeds defecated by mammals vertically (seed burial) and/or horizontally as they process and relocate dung. Although several studies have quantified this ecological function of dung beetles, very few have followed seed fate until seedling establishment, and most of these have focused on the effects of seed burial. We know very little about the effects of horizontal seed movement by dung beetles, though it is generally assumed that it will affect plant recruitment positively through diminishing seed clumping. The objective of our study was to assess the effects of dung beetle activity on the spatial distribution of seeds and seedlings, and on the probability of seedling establishment. In a tropical rainforest in Mexico we carried out two complementary field experiments for each of two tree species (Bursera simaruba and Poulsenia armata), using seeds experimentally imbedded in pig dung and recording their fate and spatial location over time. For both species, dung beetle activity reduced the spatial clumping of seeds and seedlings; however, it did not increase the probability of seedling establishment. We discuss the context- and species-specificity of the combined effects of horizontal and vertical dispersal of seeds by dung beetles, and the need to quantify long-term seedling fates to more accurately determine the effects of seed movement by dung beetles on plant recruitment.

Funding was provided by CONACYT and Instituto Politécnico Nacional (G.R.F.), Santander Mobility Award/Swansea University (A.J.K.), Wildlife Conservation Society, National Geographic Society, Leakey Foundation, National Science Foundation and the National Institute on Aging (T.J.B., J.C.B. and N.S.M.), National Geographic, CONACYT and Chester Zoo (F.A. and C.S.), UNAM PAPIIT-105015 (D.B.), NSF IOS-1255974, BCS-0715179 (T.B. and J.B.), SBE-1723237 and NIH R00-AG051764 (N.S.M.) (T.B. and J.B.) and NSF III 1514174 and David and Lucile Packard Foundation 2016-65130 (M.C.C.). Groups of animals (including humans) may showflexible grouping patterns, in which temporary aggregations or subgroups come together and split, changing composition over short temporal scales, (i.e. fission and fusion). A high degree of fission–fusion dynamics may constrain the regulation of social relationships, introducing uncertainty in interactions between group members. Here we use Shannon’s entropy to quantify the predictability of subgroup composition for three species known to differ in the way their subgroups come together and split over time: spider monkeys (Ateles geoffroyi), chimpanzees (Pan troglodytes) and geladas (Theropithecus gelada). We formulate a random expectation of entropy that considers subgroup size variation and sample size, against which the observed entropy in subgroup composition can be compared. Using the theory of set partitioning, we also develop a method to estimate the number of subgroups that the group is likely to be divided into, based on the composition and size of single focal subgroups. Our results indicate that Shannon’s entropy and the estimated number of subgroups present at a given time provide quantitative metrics of uncertainty in the social environment (within which social relationships must be regulated) for groups with different degrees of fission–fusion dynamics. These metrics also represent an indirect quantification of the cognitive challenges posed by socially dynamic environments. Overall, our novel methodological approach provides new insight for understanding the evolution of social complexity and the mechanisms to cope with the uncertainty that results from fission–fusion dynamics. Postprint

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.

The social brain hypothesis postulates the increasing complexity of social interactions as a driving force for the evolution of cognitive abilities. Whereas dyadic and triadic relations play a basic role in defining social behaviours and pose many challenges for the social brain, individuals in animal societies typically belong to relatively large networks. How the structure and dynamics of these networks also contribute to the evolution of cognition, and vice versa, is less understood. Here we review how collective phenomena can occur in systems where social agents do not require sophisticated cognitive skills, and how complex networks can grow from simple probabilistic rules, or even emerge from the interaction between agents and their environment, without explicit social factors. We further show that the analysis of social networks can be used to develop good indicators of social complexity beyond the individual or dyadic level. We also discuss the types of challenges that the social brain must cope within structured groups, such as higher information fluxes, originating from individuals playing different roles in the network, or dyadic contacts of widely varying durations and frequencies. We discuss the relevance of these ideas for primates and other animals’ societies.

Many species show fission-fusion group dynamics because it has clear advantages for flexibly exploiting heterogeneous environments. However, the mechanisms by which these dynamics arise are not well known. We used a hierarchical Bayesian model to disentangle the different influences on spider monkey (Ateles geoffroyi) individual fissions and fusions, including the three dimensions of fission-fusion dynamics (subgroup size, dispersion, and composition). Furthermore, we considered the influences of other individuals also leaving or joining a subgroup at the same time. We found that the most important influence on individual fissions and fusions is whether other individuals are also doing the same. Subgroup size and dispersion did not have clear effects on the probability that an individual fissioned or fusioned, while individuals tended to leave subgroups that were biased toward the opposite sex and to join subgroups that were biased toward their own sex. The networks constructed by the interindividual influences during fissions and fusions were cohesive and did not show assortativity by sex or by degree. Individuals had a similar degree in both networks and each was influenced by a different set of individuals, suggesting a high fluidity in the social networks. We suggest that these networks reflect the way in which information about the environment flows as individuals follow one another during fissions and fusions. Fil: Ramos Fernandez, Gabriel. Instituto Politécnico Nacional; México Fil: Morales, Juan Manuel. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Laboratorio de Ecotono; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; Argentina

Contact calls, which function to coordinate group movement and maintain contact between conspecifics, are predicted to show high levels of acoustic variability and individual distinctiveness. We investigated interindividual variation in whinnies, a contact call, between two geographically distinct communities of wild Geoffroyi’s spider monkeys (Ateles geoffroyi), which were experiencing different degrees of stability in membership due to immigration. We recorded whinnies from 18 subjects, including 9 females ranging within the Otoch Ma’ax Yetal Kooh Reserve, Punta Laguna, Mexico, and 9 females ranging within the Santa Rosa Sector, Area de Conservacion Guanacaste, Costa Rica. We examined 13 acoustic parameters of female whinnies using principal component analysis and discriminant function analysis. Individual acoustic variability was significantly different between the two communities. A higher percentage of the whinnies of females were assigned to the correct caller in the community with only 3 individuals immigrating within 36 mo before and during data collection than in the community with 15 immigrant individuals during the same period. We suggest that the variation in interindividual distinctiveness for each community was influenced by the stability of the vocal environment, which was quantitatively different between communities because of changes in membership.

© 2016 Smith-Aguilar et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 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 sociospatial 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.

In many primates, including humans, the vocalizations of males and females differ dramatically, with male vocalizations and vocal anatomy often seeming to exaggerate apparent body size. These traits may be favoured by sexual selection because low-frequency male vocalizations intimidate rivals and/or attract females, but this hypothesis has not been systematically tested across primates, nor is it clear why competitors and potential mates should attend to vocalization frequencies. Here we show across anthropoids that sexual dimorphism in fundamental frequency ( F 0 ) increased during evolutionary transitions towards polygyny, and decreased during transitions towards monogamy. Surprisingly, humans exhibit greater F 0 sexual dimorphism than any other ape. We also show that low- F 0 vocalizations predict perceptions of men's dominance and attractiveness, and predict hormone profiles (low cortisol and high testosterone) related to immune function. These results suggest that low male F 0 signals condition to competitors and mates, and evolved in male anthropoids in response to the intensity of mating competition.

Hurricanes can bring about dramatic changes to ecosystems and adversely affect animals that live in them. We monitored behavioral responses in wild spider monkeys (Ateles geoffroyi yucatanensis) in the aftermath of two hurricanes (Emily and Wilma) that moved through the Yucatan peninsula in 2005. We predicted that the monkeys would shift their diets depending on relative food availability and experience a change in the distribution of activity patterns. Because spider monkeys’ social organization is characterized by a high degree of fission–fusion dynamics, we predicted they would form smaller subgroups subsequent to the hurricanes to mitigate competition over limited food resources. We compared their responses in the immediate aftermath of Hurricane Emily and across the dry seasons before and after both hurricanes, to control for seasonal changes, by examining their activity budgets, foods consumed, and subgrouping dynamics. In the immediate aftermath of Hurricane Emily spider monkeys spent less time moving and more time feeding on leaves than before the hurricane and they were in smaller subgroups. In the dry season after both hurricanes the monkeys spent more time resting and less time moving than before the hurricanes, and leaves replaced fruit as their primary food resource. They fused into larger subgroups less often and had smaller subgroup sizes in the dry season after than before the hurricanes. Thus, the high degree of fission–fusion dynamics of spider monkeys was instrumental in affording the behavioral flexibility critical to cope with the negative post-hurricane consequences.

Flexibility in spatial cohesion allows species with high fission–fusion dynamics to exploit variable habitats and decrease the costs of feeding competition. However, coordination among highly dispersed group members becomes problematic. In spider monkeys (Ateles spp.), individuals can spread over wide areas, forming several subgroups that appear to travel independently from each other. To explore their relative travel patterns, we compare the distance between different subgroups with the distance predicted by a null model of independent travel. Observations of distance between subgroups come from simultaneous follows of ≥2 subgroups in 2 different groups of spider monkeys in Punta Laguna, Mexico. We estimated space use using the kernel method, which produces areas with a given probability of presence of the subgroups, based on the frequency with which they were observed in each location. The null model consisted of the frequency distribution of distances between randomly chosen pairs of points within the home range, choosing each point independently with a probability proportional to the corresponding observed probability of presence. In all cases, the observed distances between subgroups were very close to those predicted by the null model, which suggests that subgroups do not coordinate their relative travel patterns. Also, the distance separating 2 individuals when in different subgroups was not affected by their sex or association index. These findings underscore the low cohesiveness between group members in species with high fission–fusion dynamics and challenge us to find the mechanisms by which groups maintain their social structure.