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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.

Macaque reproductive patterns range from strictly seasonal breeding to non-seasonal breeding, but factors explaining this variation are not fully understood. Valid reproductive seasonality data are also still lacking for many wild macaque populations because the majority of birth data are from captive animals living outside of their geographic range. We evaluated whether the reproductive seasonality of wild northern pig-tailed macaques falls as expected by the ecological (latitude) or phylogenetic inertia hypotheses in comparison with other macaque species. We recorded monthly occurrences of births (N = 22), copulations (N = 563), and females exhibiting sex skin swellings (N = 18) in one group at Khao Yai National Park (KYNP), Thailand. Births, copulations, and females exhibiting sex skin swellings were significantly different from a random distribution. Using measures of circular statistics and the van Schaik and colleagues' (Schaik et al. Lee (ed), Comparative primate socioecology, Cambridge University Press, Cambridge, 1999) seasonality categorizations, the population at KYNP is best characterized as moderately seasonal breeding. Despite some inconsistency, macaque reproductive seasonality was significantly influenced by latitudinal location. We broadly found that: (1) non-seasonal breeding macaque populations (birth r-vector 0.3) lived at latitudes close to the equator between 1°S and 3°N, (2) moderately seasonal breeding macaque populations (0.3 birth r-vector 0.7) were found between 3°N and 14°N and at 5°S, and (3) strictly seasonal breeding macaque populations (birth r-vector 0.7) ranged ≥ 12°N. A strong phylogenetic signal in reproductive seasonality on the macaque phylogeny was also detected. However, further studies of wild macaque populations are still needed to better characterize reproductive seasonality in this taxon.

One of the goals in animal socioecology is to understand the functions and dynamics of group living. While observations of free-ranging animals are a crucial source of information, an experimental investigation that manipulates the size or composition, or both, of animal groups in captivity can also bring complementary contributions to the research inquiry. When paired with an automatic data collection by biologging technology, experimental studies on captive animals also allow for big data analyses based on recent machine learning techniques. As an initial exploration of this research paradigm, the present study inquired to what extent isolation of captive Japanese macaques (Macaca fuscata) changed their movement patterns. Using three-dimensional location trajectories of the macaques that were systematically collected via Bluetooth Low Energy beacons and a deep neural network, we estimated the identifiability of whether a macaque was behaving in isolation or in group. We found that the neural network identified the isolation vs. in-group conditions with more than 90% accuracy from a five-minute location trajectory, suggesting that the isolation caused notable changes from the canonical group-living behaviors. In addition, the isolation made each individual more identifiable from one another based on their location trajectories.

The transition from solitary life to sociality is considered one of the major transitions in evolution. In primates, this transition is currently not well understood. Traditional verbal models appear insufficient to unravel the complex interplay of environmental and demographic factors involved in the evolution of primate sociality, and recent phylogenetic reconstructions have produced conflicting results. We therefore analyze a theoretical model for the evolution of female social philopatry that sheds new light on the question why most primates live in groups. In individual-based simulations, we study the evolution of dispersal strategies of both resident females and their offspring. The model reveals that social philopatry can evolve through kin selection, even if retention of offspring is costly in terms of within-group resource competition and provides no direct benefits. Our model supports the role of predator avoidance as a selective pressure for group-living in primates, but it also suggests that a second benefit of group-living, communal resource defense, might be required to trigger the evolution of sizable groups. Lastly, our model reveals that seemingly small differences in demographic parameters can have profound effects on primate social evolution.

A growing body of work demonstrates that a species’ socioecology can impact its cognitive abilities. Indeed, even closely related species with different socioecological pressures often show different patterns of cognitive performance on the same task. Here, we explore whether major differences in social tolerance in two closely related macaque species can impact a core sociocognitive ability, the capacity to recognize what others see. Specifically, we compared the performance of Barbary macaques (Macaca sylvanus, n = 80) and rhesus macaques (Macaca mulatta, n = 62) on a standard test of visual perspective understanding. In contrast to the difference in performance, one might expect from these species’ divergent socioecologies that our results show similar performance across Barbary and rhesus macaques, with both species forming expectations about how another agent will act based on that agent’s visual perspective. These results suggest that differences in socioecology may not play as big of a role in the evolution of some theory of mind capacities as they do in other decision-making or foraging contexts.

Museum collections are critical resources for examination of comparative anatomy, developmental biology, and life history hypotheses. Skeletal collections provide insight into spatiotemporal, species, population, and individual variation associated with environmental, social, and epidemiological history. For endangered species such as great apes, these collections provide data that are nearly impossible to replicate today. In this second in a series of articles reviewing the great ape holdings of the Peabody Museum of Natural History at Yale University, we describe the Gorilla gorilla skeletal collection, comprising 16 individuals: 13 males, 2 females, and 1 of indeterminate sex. Evidence of socioecology, interindividual violence, hunting, captive management, predation, senescence, and infectious disease are present within the skeletal material. The collection exhibits possible taxonomic diversity as well. Our evaluation of the Yale Peabody Museum collection provides a baseline for future research and testable hypotheses for alternate techniques, such as isotopic analyses of dental calculus and noninvasive genetic testing. Museum collections continue to provide new insights into taxonomic and individual variation and environmental context, and ultimately allow for comparisons between modern and historical environmental and behavioral variables.

Squirrel monkeys are a long‐standing biomedical model, with multiple species and subspecies housed in research facilities. Few studies have examined the developmental differences between these subspecies, which may affect research outcomes. The primate neonatal neurobehavioral assessment was completed at 2 weeks of age with 279 dam‐reared squirrel monkeys (188 Saimiri boliviensis boliviensis, 45 S. b. peruviensis, and 46 Saimiri. sciureus sciureus). Activity, orientation to stimuli, state control, and motor maturity scores, as well as startle responses and number of vocalizations were compared across subspecies and sex using factorial analysis of covariance (ANCOVAs) controlling for birthweight. There were no differences in orientation or motor maturity scores (p > .05) among the three subspecies or between sexes; however, there were significant subspecies differences in motor activity and state control scores. Of the three subspecies, S. s. sciureus has the lowest state control and activity scores (p < .05). They also had the most exaggerated startle response/aversion to a sudden loud noise, vocalized significantly less, and were less likely to resist restraint during the assessment (p < .05). The three subspecies of squirrel monkeys did not differ in motor development and attention to external stimuli but were significantly different in state control and activity levels. Overall S. s. sciureus were less active, agitated, irritable, and easier to console compared to S. b. boliviensis and S. b. peruviensis. This supports field research on socioecology which documented different social structure and behavior in wild populations of S. s. sciureus compared to S. b. boliviensis and S. b. peruviensis.

A key goal in behavioral ecology is to investigate the factors influencing the access to food resources and energetic condition of females, which are strong predictors of their reproductive success. We aimed to investigate how ecological factors, social factors, and reproductive state are associated with energetic condition in a wild neotropical primate using non-invasive measures. We first assessed and compared urinary C-peptide levels (uCP), the presence of urinary ketones (uKet), and behaviorally assessed energy balance (bEB) in female white-faced capuchin monkeys (Cebus imitator) living in Santa Rosa, Costa Rica. Then, we assessed how these measures were associated with feeding competition, dominance rank, and reproductive state. As predicted, uCP and bEB were positively associated with each other, and bEB was negatively associated with uKet. However, we did not find a relationship between uCP and uKet. Females showed lower uCP and bEB values during periods of intense feeding competition, but this relationship was not dependent on dominance rank. Furthermore, rank was not directly associated with uCP and bEB. Urinary ketones, on the other hand, were only produced in the most adverse conditions: by low-ranking, lactating females during periods of intense feeding competition. Behavioral strategies are assumed to maximize reproductive success and not energetic condition per se, which might explain why rank was not generally associated with energetic condition in our study population. This highlights the importance of considering potential differences between reproductive success and proxies of reproductive success, such as energetic condition or food intake, when investigating predictions of socioecological models.

Facial displays (or expressions) are a primary means of visual communication among conspecifics in many mammalian orders. Macaques are an ideal model among primates for investigating the co-evolution of facial musculature, facial displays, and social group size/behavior under the umbrella of "ecomorphology". While all macaque species share some social behaviors, dietary, and ecological parameters, they display a range of social dominance styles from despotic to tolerant. A previous study found a larger repertoire of facial displays in tolerant macaque species relative to despotic species. The present study was designed to further explore this finding by comparing the gross morphological features of mimetic muscles between the Sulawesi macaque (Macaca nigra), a tolerant species, and the rhesus macaque (M. mulatta), a despotic species. Five adult M. nigra heads were dissected and mimetic musculature was compared to those from M. mulatta. Results showed that there was general similarity in muscle presence/absence between the species as well as muscle form except for musculature around the external ear. M. mulatta had more musculature around the external ear than M. nigra. In addition, M. nigra lacked a zygomaticus minor while M. mulatta is reported to have one. These morphological differences match behavioral observations documenting a limited range of ear movements used by M. nigra during facial displays. Future studies focusing on a wider phylogenetic range of macaques with varying dominance styles may further elucidate the roles of phylogeny, ecology, and social variables in the evolution of mimetic muscles within Macaca Anat Rec, 299:1317-1324, 2016. © 2016 Wiley Periodicals, Inc.

Humans are unusual in having stable male-female breeding bonds within multi-level societies. Such societies are not found in other apes, but have evolved independently in other primates, including several African papionins: hamadryas and Guinea baboons and gelada monkeys. Stable breeding bonds have been proposed to evolve either (1) because males can monopolize females when food distribution forces females to forage in small groups or (2) because females exchange exclusive mating for male services, such as protection from infanticide. Comparative studies are needed to test these hypotheses. In the meantime, we used an agent-based computer model to test the plausibility of these hypotheses. We simulated primates living in social groups within a larger population using a model we call BEGET (Behavior, Ecology, Genetics, Evolution, and Tradeoffs), which employed decision vectors, experimental evolution, realistic trade-offs, and phenotypic plasticity. We employed experimental evolution to generate male genotypes that varied in their competitive ability and in their long-term mating strategy. "Rover" males searched for and mated with any sexually receptive females whereas "Loyalist" males formed stable associations with particular groups of females. Much like living primates, the virtual primates exhibited tradeoffs between contest and scramble competition for access to females: Loyalists evolved larger body size than Rovers. We tested the effect of female foraging group size and the presence of infanticide and infant protection on the relative success of these strategies. We found that Loyalists achieved greater reproductive success than Rovers only when females were in groups smaller than four. Both Rovers and Loyalists sometimes evolved infanticidal behavior, but the presence of infanticide benefited Rovers rather than Loyalists, suggesting that the evolution of stable breeding bonds depends on the spatial distribution of females, rather than the risk of infanticide.

Objectives How social groups govern their distribution in time and space is a central question in socioecology. The aim of this study is to explore the role of acoustic signaling for spacing and cohesiveness in a nocturnal, cohesive, pair-living strepsirrhine. Material and Methods The study was conducted in northwestern Madagascar. Six pairs of Avahi occidentalis were radio-collared and home range usage, vocalizations and call-associated behavior recorded using GPS-based focal animal sampling. Home range size was analyzed using ArcView GIS 3.3. Calls were characterized by a multiparametric sound analysis. Results Three frequently used, acoustically distinct call types were identified: the avahee call, the whistle call, and the growling call, the latter is a soft; the two others are loud calls. Call types are given by both sexes and convey individually-specific signatures. Call types are used primarily in the locomotion context in the non-core-area of home ranges. The least common avahee call is responded by the avahee call from farther away. The more common whistle call, given when partners become visually isolated, and the growling call emitted at close distances, were answered by the whistle and the growling call. Results suggest a spacing function for the avahee call and group coordination functions for the other call types. Discussion Our study provides first empirical evidence for a nocturnal, cohesive pair-living strepsirrhine that vocal signaling represents an important mechanism for spacing, group coordination and decision making. Findings contribute to a better understanding of the evolutionary roots of primate vocal communication

Recent comparative studies on the evolution of mammalian sociality came to opposite conclusions regarding the direction and drivers of evolutionary transitions in social organization, particularly concerning the evolution of pair-living among primates. Because the genus Eulemur is one of the few exceptional primate genera that contain both group- and pair-living species, eulemurs offer a rare opportunity to illuminate the processes driving social diversity among species with very similar life histories and ecologies. The aims of our study were therefore 1) to reconstruct the evolution of social organization in eulemurs with new demographic and phylogenetic data and 2) to evaluate several hypotheses about the evolution of pair-living with data from our long-term study of Eulemur rufifrons and published data on other eulemurs. Our review of published data confirmed that E. mongoz and E. rubriventer are pair-living, whereas the 10 other species of Eulemur live in groups with multiple adult males and females. Furthermore, pair-living evolved at least once among eulemurs from group-living ancestors. The available comparative evidence indicated that this evolutionary transition was probably not driven by male infanticide, social instability, or singular ecological factors. Instead, we propose that female competition has favored small female group size and that this effect may have been exacerbated by interspecific competition with sympatric congeners in the ancestors of the pair-living species. In conclusion, we confirmed that the evolution of pair-living from group-living ancestors among true lemurs is exceptional, but not unique, among mammals, and that commonly invoked hypotheses for the evolution of pair-living do not appear to be supported for this genus.

Vector-borne diseases of importance to human and domestic animal health are listed and the increasing emergence of syndromes, new epidemiological cycles and distributions are highlighted. These diseases involve a multitude of vectors and hosts, frequently for the same pathogen, and involve natural enzootic cycles, wild reservoirs and secondary epidemiological cycles, sometimes affecting humans and domestic animals. On occasions the main reservoir is in the domestic environment. Drivers for secondary cycles are mainly related to human impacts and activities and therefore, for purposes of prevention and control, the focus needs to be on the socioecology of the diseases. Technical and therapeutical solutions exist, and for control there needs to be a clear understanding of the main vertebrate hosts or reservoirs and the main vectors. The targets of interventions are usually the vector and/or secondary epidemiological cycles and, in the case of humans and domestic animals, the spillover or incidental hosts are treated. More attention needs to be given to the importance of the political economy in relation to vector-borne diseases, as many key drivers arise from globalisation, climate change and changes in structural ecologies. Attention to reducing the risk of emergence of new infection cycles through better management of the human-animal-environment interface is urgently needed.

Multidimensional approaches support audiovisually coevolved large noses on the unique society of proboscis monkeys., Male proboscis monkeys have uniquely enlarged noses that are prominent adornments, which may have evolved through their sexually competitive harem group social system. Nevertheless, the ecological roles of the signals encoded by enlarged noses remain unclear. We found significant correlations among nose, body, and testis sizes and a clear link between nose size and number of harem females. Therefore, there is evidence supporting both male-male competition and female choice as causal factors in the evolution of enlarged male noses. We also observed that nasal enlargement systematically modifies the resonance properties of male vocalizations, which probably encode male quality. Our results indicate that the audiovisual contributions of enlarged male noses serve as advertisements to females in their mate selection. This is the first primate research to evaluate the evolutionary processes involved in linking morphology, acoustics, and socioecology with unique masculine characteristics.

Our understanding of chemical signals in mammals derives principally from studies in which researchers examine signal structure or function within a single species. Despite the unique information to be gained from applying comparable methods across multiple species, comparative studies of chemical signals are extremely limited. Here, we review the available literature on the evolution of chemosignals in male and female strepsirrhine primates (galagos, lorises and lemurs), all of which rely heavily on chemical communication. We draw from a few case studies, but focus our review on two comparative studies. In one, researchers examined the volatile chemical composition of urinary signals across 12 species representing most families within Strepsirrhini, including six 'urine-marking' species and six glandular or 'nonurine-marking' species. In the other, researchers examined the volatile chemical composition of glandular signals in eight Eulemur species differing in social or dominance structure. We highlight five findings. (1) Regardless of the scent source, chemical profiles differ substantially between species, providing reliable species 'scent signatures'. None the less, (2) urine markers express more compounds and have more distinguishable species scent signatures in their urine than do nonurine markers, suggesting specialization of function. Within Eulemur (3) chemical richness is greater in multimale-multifemale species than in pair-bonded species. Moreover, (4) whereas chemical richness of male signals is greater in sexually codominant species, chemical richness of female signals is greater in female-dominant species. Together, the findings from both comparative studies, coupled with case studies, suggest that signal richness is linked to some aspect of the focal species' socioecology. Lastly, (5) regardless of the scent source, strepsirrhine chemosignals evolve gradually over time, but at fast rates and homogeneously within different lineages. Comparative studies reveal patterns that cannot be detected from the single-species approach and are therefore critical for providing new insight into the function and evolution of olfactory signals.

Our recent work on Monk Parakeets (Myiopsitta monachus) reported dominance steepness values that were inaccurate because of a bug in the analysis program. Updated steepness values are more moderate than initially reported, which places captive Monk Parakeet groups midway between egalitarianism and despotism.

The prime-adult-dominated mortality profile of large bovids in the 1.8 Ma FLK Zinj assemblage, Olduvai Gorge, Tanzania, was recently attributed to ambush hunting by early Homo (Bunn, H.T., Pickering, T.R. 2010. Quat. Res. 74, 395–404). We now investigate a logical follow-up question: is enough known about the causes and pervasiveness of prime-adult-dominated mortality profiles (defined as >70% prime adults) from modern ecosystems and from archaeological sites to warrant their attribution solely to hominin hunting? Besides hominin hunting, three methods of scavenging could have provided the large bovids butchered at FLK Zinj: first-access scavenging from non-predator-related accidents; late-access passive scavenging from lion (or other) kills; early-access aggressive scavenging from lion (or other) kills. We present new data on hunted prey from Hadza bow hunting (e.g., N = 50 impala; N = 18 greater kudu) near Lake Eyasi, Tanzania, and from San bow hunting (N = 13 gemsbok) in the Kalahari Desert, Botswana, documenting non-selective, living-structure profiles. We present new data on drowned wildebeest (N = 175) from Lake Masek, in the Serengeti, documenting many prime adults but also a significantly high percentage of old adults, unlike the profile at FLK Zinj. We also examine mortality profiles from modern African lions and from Old World Pleistocene archaeological sites, revealing that while prime-dominated profiles are present in some archaeological assemblages, particularly some Late Pleistocene European sites involving cervids, they are not documented from lion or other larger carnivore predation; moreover, living-structure profiles with prime adults representing ∼50–60% of prey are common, particularly in African archaeological assemblages involving bovids hunted by humans. Although taphonomic bias, prey socioecology, and season of death may all influence mortality profiles, prime-dominated profiles require careful evaluation. The prime-dominated profile at FLK Zinj is significantly different from profiles formed by the three scavenging methods, which likely indicates hunting by Early Pleistocene Homo.

Bearded sakis (Chiropotes spp.) are among the least known primates in the world, particularly with regard to their social organization. However, extremely large and variable group size and growing evidence for affiliative relationships among males, make them a fascinating subject for studies of male–male tolerance and the evolution of large groups. During a 13-month study of free ranging Guianan bearded sakis (Chiropotes sagulatus) in continuous forest in Suriname, we documented variation in group size seasonally and social behaviour, particularly among males. We found that group size was smaller and more variable in the long dry season than the short wet season, perhaps in response to changes in resource availability. We found clear evidence of affiliative male–male relationships, with males being more social than females (89.2% of events involved one male versus 15.6% that involved one female) and typically socializing with other males (68.7% of events involved 2 or more males). We also found no evidence of hierarchical relationships between males (complete absence of agonistic interactions), and we documented unique male-affiliative behaviours and temporary all-male subgroups for the first time. To investigate potential explanations of male tolerance, we compared bearded saki social patterns to other multi-male group living primates (Ateline and Pan spp.). We found similarities with Brachyteles that suggest high intergroup mating competition and scramble competition for mates within groups.

Although predation has likely played a central role in the evolution of primate socioecology, we currently lack a thorough understanding of how fine-scale variation in perceived predation risk affects primates’ short-term space use patterns and predator avoidance strategies. We examined the spatial and ecological characteristics of predator encounters, as well as behavioral responses to perceived predation risk, in 5 groups of wild white-faced capuchins (Cebus capucinus) in Costa Rica over a 1.5-year period. Alarm-calling bouts directed at birds were more likely to originate in high forest strata, whereas alarm-calling bouts at snakes and terrestrial quadrupeds were more likely to originate near the ground. Relative risk maps based on the locations of predator encounters revealed that high-risk areas for birds and for all guilds combined consisted of more mature forest, whereas low-risk areas for these predators consisted of relatively younger forest. The animals were most vigilant near the ground, which may reflect greater perceived exposure to snakes and terrestrial predators in lower vertical levels. Incorporating the combined risk function into a predictive model of vigilance behavior improved prediction relative to null models of uniform risk or habitat-specific risk. Our results suggest that capuchin monkeys in this study system perceive reduced predation risk in the high and middle forest layers, and they adjust their vigilance behavior to small-scale spatial variation in perceived risk.

Effectively characterizing primate diets is fundamental to understanding primate behavior, ecology and morphology. Examining temporal variation in a species' diet, as well as comparing the responses of different species to variation in resource availability, can enhance understanding of the evolution of morphology and socioecology. In this study, we use feeding data collected over five years to describe the diets of two sympatric Southeast Asian primate species of similar body size: white-bearded gibbons (Hylobates albibarbis) and red leaf monkeys (Presbytis rubicunda rubida), in Gunung Palung National Park, West Kalimantan, Indonesia. Long-term data sets are especially important for characterizing primate diets in Southeast Asia, where the forests exhibit supra-annual mast fruiting events. We found that gibbons were mainly frugivorous, with fruit and figs comprising 70% of their 145 independent feeding observations, whereas leaf monkeys ate a substantial amount of seeds (26%), fruits and figs (26.5%) and leaves (30%, n = 219 independent feeding observations). Leaf monkeys consumed a higher number of plant genera, and this was due mostly to the non-frugivorous portion of their diet. To investigate resource selection by these primates we utilized two different approaches: the Manly Selectivity Ratio, which did not take into account temporal variation of resource availability, and a model selection framework which did incorporate temporal variation. Both species selected figs (Ficus) more than predicted based on their availability under the Manly Selectivity Ratio. Model selection allowed us to determine how these primates alter the proportion of leaves, flowers, seeds, figs and fruit in their diets in response to variation in fruit availability. When fruits were scarce, both gibbons and leaf monkeys incorporated more leaves and figs into their diets, indicating that these two food classes are fallback foods for these primates. We discuss how different measures of resource selection can provide seemingly contradictory results, and emphasize the importance of long term studies that combine independent feeding observations with rigorous assessment of temporal variation in resource availability when modelling feeding selectivity.

Objectives Great apes show considerable diversity in socioecology and life history, but knowledge of their physical growth in natural settings is scarce. We characterized linear body size growth in wild mountain gorillas from Volcanoes National Park, Rwanda, a population distinguished by its extreme folivory and accelerated life histories. Methods In 131 individuals (0.09–35.26 years), we used non-invasive parallel laser photogrammetry to measure body length, back width, arm length and two head dimensions. Nonparametric LOESS regression was used to characterize cross-sectional distance and velocity growth curves for males and females, and consider links with key life history milestones. Results Sex differences became evident between 8.5 and 10.0 years of age. Thereafter, female growth velocities declined, while males showed increased growth velocities until 10.0–14.5 years across dimensions. Body dimensions varied in growth; females and males reached 98% of maximum body length at 11.7 and 13.1 years, respectively. Females attained 95.3% of maximum body length by mean age at first birth. Neonates were 31% of maternal size, and doubled in size by mean weaning age. Males reached maximum body and arm length and back width before emigration, but experienced continued growth in head dimensions. Conclusions While comparable data are scarce, our findings provide preliminary support for the prediction that mountain gorillas reach maximum body size at earlier ages compared to more frugivorous western gorillas. Data from other wild populations are needed to better understand comparative great ape development, and investigate links between trajectories of physical, behavioral, and reproductive maturation.

Spotted hyenas (Crocuta crocuta) are large mammalian carnivores, but their societies, called ‘clans’, resemble those of such cercopithecine primates as baboons and macaques with respect to their size, hierarchical structure, and frequency of social interaction among both kin and unrelated group-mates. However, in contrast to cercopithecine primates, spotted hyenas regularly hunt antelope and compete with group-mates for access to kills, which are extremely rich food sources, but also rare and ephemeral. This unique occurrence of baboon-like sociality among top-level predators has favoured the evolution of many unusual traits in this species. We briefly review the relevant socioecology of spotted hyenas, document great demographic variation but little variation in social structure across the species’ range, and describe the long-term fitness consequences of rank-related variation in resource access among clan-mates. We then summarize patterns of genetic relatedness within and between clans, including some from a population that had recently gone through a population bottleneck, and consider the roles of sexually dimorphic dispersal and female mate choice in the generation of these patterns. Finally, we apply social network theory under varying regimes of resource availability to analyse the effects of kinship on the stability of social relationships among members of one large hyena clan in Kenya. Although social bonds among both kin and non-kin are weakest when resource competition is most intense, hyenas sustain strong social relationships with kin year-round, despite constraints imposed by resource limitation. Our analyses suggest that selection might act on both individuals and matrilineal kin groups within clans containing multiple matrilines.

Studies of chemical signals in vertebrates typically target single species; however, a broader understanding of olfactory communication may derive from comparative studies. We collected urine from 12 species representing most families of strepsirrhine primates--an excellent model clade because of variation in scent marking and socioecology. Using SPDE/GC-MS, we identified the volatile chemical composition of male and female urine from six 'urine marking' species and six glandular or 'non-urine marking' species. We found no sex differences, but as predicted, urine markers expressed the most chemically complex and distinctive urine. More distantly related species had more dissimilar urinary profiles, suggesting gradual signal evolution. Reconstructing ancestral chemical profiles revealed different evolutionary trajectories for urine and non-urine markers. We suggest that urine marking is an ancestral behaviour related to solitary, nocturnal living and that parallel evolutionary shifts towards greater reliance on derived glandular marking occurred in a family (Lemuridae) characterized by diurnality and sociality.

Socioecology suggests that female distribution in space is determined by the distribution of food resources and the male distribution is influenced by female distribution. Though studies have traditionally focused on females, males have received increasing attention in recent years. We compared male–male relationships in lion-tailed macaques and bonnet macaques. Because bonnet macaques have a high adult male:female sex ratio and are seasonal breeders whereas lion-tailed macaques have a low adult male:female sex ratio and are largely aseasonal breeders, we predicted that bonnet macaque males would be spatially and socially more tolerant of each other and would have less linear dominance relationships than lion-tailed macaques. We recorded male–male and male–female relationships in 1 group of wild macaques of each species via scan sampling and 1–0 sampling. The results revealed that lion-tailed macaque males largely remained at a distance from each other whereas bonnet macaque males remained in close proximity to one another. Lion-tailed macaque males were more agonistic toward each other whereas bonnet macaque males showed more affiliative interactions. The dominance hierarchy among lion-tailed macaque males was more linear than among bonnet macaque males. Our data support the hypothesis that the study of spatial structuring, temporality of interactions, and linearity of social relationships may contribute to a better understanding of macaque social systems.

Variation in ranging behavior, social organization, and feeding ecology among capuchins (Cebus spp.) is a classic example of how closely related species may be differentially adapted to their local environments. Marked differences in all 3 areas occur among Cebus spp. between the untufted capuchins (Cebus capucinus, C. olivaceous, and C. albifrons) and the tufted capuchins (C. apella, C. xanthosternos, C. nigritus, and C. libidinosus). The key socioecological distinction between the 2 groups has traditionally been that, compared with the tufted group, untufted capuchins eat more ripe foods, as befits their more gracile masticatory system; range more broadly in search of high-quality foods; and live in larger groups with more males and more agonistic interactions between groups. Here I assess how well the basic socioecological characteristics —activity budget, ranging— of previously unstudied Ecuadorian Cebus albifrons fit within this model. Few researchers have conducted studies on Cebus albifrons, despite its prominent role in the initial development of the model for socioecology of Cebus. The results of my 1-yr study of a single social group support the model’s general characterization of untufted capuchins in ranging and feeding behaviors, but also suggest that direct ecological and demographic effects, in addition to adaptation to local conditions, may explain additional variation in group size across species of Cebus.

The Ivory Coast's Tai Forest is home to a diverse primate fauna, including eight monkey species that interact daily with the environment, each other, and a web of predators. These interactions have led to an array of adaptations, some of which conform to theoretical expectations, and others are at odds with current behavioral ecology models. In this paper, we draw on fifteen years of observations to examine two central issues. First, how do broad trends in diet and resource distribution influence group size and levels of sociality? Second, what mechanisms are used to counter pressures exerted by the predator community? The general picture that emerges is that while the pressure exerted by predators at Tai has led to a host of behavioral and cognitive adaptations, it is food preferences and foraging habits, not predation pressure, that are the main determinants, not only of group size, but also its direct consequences - mating systems and sociality levels.

Field studies on Japanese macaques on Yakushima Island started in the mid-1970s, >25 yr after the emergence of Japanese primatology, in response to criticism of methods using provisioning and the desire to find the socioecological factors influencing the social life of macaques in natural habitats. We habituated macaques without provisioning mainly in the coastal warm-temperate forest and found that they lived in small troops with a high socionomic sex ratio. Observations of several troop fissions and troop takeovers by nontroop males suggest that Yakushima macaques have a different social organization from that of Japanese macaques in other habitats. For example, youngest ascendancy as the dominance relationhip among sisters, which usually occurs in provisioned troops, was absent in Yakushima macaques. We compared their ecological and social features with those of Japanese macaques at Kinkazan (cool-temperate forests) and found that abundance of high-quality foods may cause stronger intra- and intertroop competition at Yakushima. Female Yakushima macaques may more positively solicit nontroop males to associate with them during the mating season. Such a tendency may promote frequent male movement between troops and frequent troop fissions. Though ecological factors form social features of Japanese macaques, some features such as male association and movements between troops are not accounted for via socioecology. Recent field studies have focused on macaques living at higher altitudes in Yakushima and on individual survival strategies by taking diverse viewpoints and using new technologies. DNA analysis of fecal samples shows low genetic diversity and suggests the macaques’ recent expansion from lowland to highland forests in Yakushima. The population censuses conducted annually indicate that the higher-altitude macaques have a larger home range but a similar group size versus their counterparts at low elevations. The unsolved issues in socioecology will pose a challenge to the younger generation of primatologists. Conservation of macaques and their habitat is one of our major activities at Yakushima. The level of protection has gradually increased in the National Park at Yakushima and, via our various conservation efforts, its most important area was designated a World Heritage Site by UNESCO in 1993. However, large-scale logging in the 1960s and 1970s caused the loss of macaque habitats and led to increased crop damage by them in the 1980s. We have proposed effective methods to protect cultivated fields from macaques as well as several plans for sustainable use of forests, such as ecotourism and a fieldwork course for university students. Local residents and researchers have created several nongovernment organizations (NGOs) to promote conservation and nature study at Yakushima. The role of local NGOs is particularly important to mitigate conflicts between people and wildlife. Though hundreds of macaques are still captured as pests annually in Yakushima, we continue the conservation measures and spread awareness of conservation in cooperation with the local NGOs.

Science is fairly certain that the gorilla lineage separated from the remainder of the hominoid clade about eight million years ago,2, 4 and that the chimpanzee lineage and hominin clade did so about a million years after that.1, 2 However, just this year, 2007, it was discovered that although the human head louse separated from the congeneric chimpanzee body louse (Pediculus) around the same time as the chimpanzee and hominin lineages split,3 the human pubic louse apparently split from its sister species, the congeneric gorilla louse, Pthirus, 4.5 million years after their host lineages split.3 No tested explanations exist for the discrepancy. Much is known about hominin evolution, but much remains to be discovered. The same is true of primate socioecology in general and gorilla socioecology in particular.

Escalated aggression has been studied both theoretically and empirically in many species of organisms. Most studies have focused on individuals competing for mates, territories or rank within a social hierarchy. In nonhuman primates, dyadic aggression has been studied in the context of feeding trees, whereas coalitions have been studied primarily in the context of mate or rank acquisition. Although coalitions can represent a substantial fraction of agonistic interactions at feeding trees, most studies have not taken into account the effect of present ecological conditions on the occurrence of coalition formation. We examined whether there is an ecological basis to escalated aggression, defined as overt dyadic aggression and polyadic coalition formation, in wild white-faced capuchin monkeys, Cebus capucinus. Our results indicate that ecological characteristics of the feeding trees, the availability of potential allies and rank differences between interactants are important in predicting escalated aggression in this species. This is the first field study to link ecology to escalations in the form of dyadic and polyadic aggression in nonhuman primates.

Food abundance and distribution have played a central role in the conceptual theory of primate socioecology [Janson, Behaviour 105:53–76, 1988; Isbell, Behavioral Ecology 2:143–155, 1991; Sterck et al., Behavioral Ecology and Sociobiology 41:291–309, 1997; van Schaik, In: Standen V, Foley RA, editors, Comparative Socioecology. Oxford: Blackwell. p 195–218, 1989]. This theory predicts that agonistic (“contest”) competition should occur when food is distributed in discrete, defensible patches; in contrast, when food sources are distributed uniformly or randomly, non-agonistic (“scramble”) competition is expected. Primatologists usually measure resource density and patchiness from a botanical perspective, ignoring the biology of the animal being studied. Such an approach may be irrelevant in terms of how animals view the dispersion of resources. Using a novel focal-tree method that measures resource availability on a scale that is both spatially and temporally relevant to the animal under investigation, we take a cost-benefit approach to predict the frequency of food-related agonism in white-faced capuchin monkeys (Cebus capucinus) from 11 ecological and social variables. We retained four variables in the regression model: two representing the opportunity for aggression (i.e., feeding bout length and the number of feeding adult females), and two representing opportunity costs (i.e., fruit abundance and the number of potential feeding sites in the focal tree). The results of this study indicate that the amount of food-related aggression in white-faced capuchins can be predicted by variables representing the costs and benefits of contesting a food resource. Am. J. Primatol. 69:533–550, 2007. © 2006 Wiley-Liss, Inc.

The orang-utan is unique among apes in having an unusually long male developmental period and two distinct adult male morphs (flanged and unflanged), which generally, but not exclusively, employ different reproductive strategies (call-and-wait vs. sneak-and-rape). Both morphs have recently been shown to have roughly similar levels of reproductive success in the one site where such a study has been conducted. This is in stark contrast to the unimale polygynous gorilla, in which dominant males sire almost all infants. Despite this, evidence on sexual dimorphism, life history, diet, and socioecology of extant and extinct apes, as well as the ontogeny, reproductive morphology, and physiology of extant apes, all indicate that the orang-utan's present-day mating system most likely evolved from a gorilla-like base, with one dominant male guarding a harem of females. The available evidence indicates that, due chiefly to the likely onset of the El Niño Southern Oscillation (generally regarded as the trigger for mast fruiting in dipterocarps) approximately 3-5Ma, southeast Asian forests would have begun to experience longer and more severe periods of low food availability. This change in food availability would have meant that full-time gregariousness was no longer energetically tolerable and, as a result, females dispersed more widely in search of food and adult/flanged males were no longer able to effectively guard a harem of females. A niche for a quiet, quick, opportunistic "sexual predator" (i.e., the unflanged male) then became available. This finding implies that, despite being anatomically quite chimpanzee-like, the ancestral hominoid probably had a social and mating system more similar to the gorilla than any other living ape.

Relationships between conspecifics are influenced by both ecological factors and the social organization they live in. Systematic variation of both--consistent with predictions derived from socioecology models--is well documented, but there is considerable variation within species and populations that is poorly understood. The mountain gorilla (Gorilla beringei) is unusual because, despite possessing morphology associated with male contest competition (e.g., extreme sexual dimorphism), they are regularly observed in both single-male and multimale groups. Both male-female and male-infant bonds are strong because males provide protection against infanticide and/or predation. Risk of these threats varies with social structure, which may influence the strength of social relationships among group members (including females and offspring, if females with lower infant mortality risk are less protective of infants). Here, we investigate the relationship between group structure and the strength of proximity relationships between males and females, males and infants, and females and offspring. Data come from 10 social groups containing 1-7 adult males, monitored by the Dian Fossey Gorilla Fund's Karisoke Research Center in Volcanoes National Park, Rwanda. After controlling for group size and infant age, association strength was similar for male-female pairs across group types with both dominant and nondominant males, but male-infant relationships were strongest in single-male groups where paternity certainty was high and animals had fewer social partners to choose from. The male:female and male:infant ratios better predicted both male-female and male-infant associations than the absolute number of males, females, or infants did. The fewer the number of males per female or infant, the more both pair types associated. Dominant males in groups containing fewer males had higher eigenvector centrality (a measure of importance in a social network) than dominant males in groups with more males. Results indicate that nondominant males are an important influence on relationships between dominant males and females/infants despite their peripheral social positions, and that relationships between males and infants must be considered an important foundation of gorilla social structure.

Female social dominance (FSD) over males is unusual in mammals, yet characterizes most Malagasy lemurs, which represent almost 30% of all primates. Despite its prevalence in this suborder, both the evolutionary trajectory and proximate mechanism of FSD remain unclear. Potentially associated with FSD is a suite of behavioural, physiological and morphological traits in females that implicates (as a putative mechanism) ‘masculinization’ via androgen exposure; however, relative to conspecific males, female lemurs curiously show little evidence of raised androgen concentrations. By observing mixed‐sex pairs of related Eulemur species, we identified two key study groups ‐‐ one comprised of species expressing FSD and increased female scent marking, the other comprised of species (from a recently evolved clade) showing equal status between the sexes and the more traditional pattern of sexually dimorphic behaviour. Comparing females from these two groups, we show that FSD is associated with more masculine androgen profiles. Based on the widespread prevalence of male‐like features in female lemurs and a current phylogeny, we suggest that relaxation of hormonally mediated FSD emerged only recently and that female masculinization may be the ancestral lemur condition, an idea that could revolutionize our understanding of the ancient socioecology and evolution of primate social systems.

In this paper, we investigate the formation and function of the multilevelled, fission–fusion social structure in a free-ranging African elephant, Loxodonta africana, population. We quantitatively identified the existence of four social tiers by using cluster analysis on individual association data. We assessed the effects of season and study period on social structuring and levels of cohesion within and among social units. We found that second-tier units, potentially the equivalent of the ‘family’, were stable across seasonal periods but the number of units increased as the study progressed and the population grew. It appears that these units were sufficiently small not to be influenced by ecologically related factors, such as resource competition, that might otherwise lead to them splitting. On the other hand, third- and fourthtier units were significantly affected by season in a way that suggests a trade-off between ecological costs (e.g. from resource competition) and different social and ecological benefits (e.g. from predator defence, territoriality, knowledge sharing and rearing of young). Age structure also appeared to influence this multitiered social organization. The size of second-tier social units was significantly affected by the age of matriarchs: units lead by matriarchs likely to be grandmothers (i.e. females 35 years and older) were significantly larger than those lead by younger matriarchs. We present a conceptual framework for understanding the emergence of multiple-tier social structure from interactions driven by socioecological processes. This study is the first to use rigorous quantitative methods to statistically show the existence of four hierarchical tiers of social organization in a nonhuman animal. Additionally, our results elucidate the role that ecological processes play in producing complex social structures.

The effects of human activity on population and social structure are a pantropical concern for primate conservation. We compare census data and social group counts from two forests in the Udzungwa Mountains, Tanzania. The main aim is to relate differences within and between the forests to current theory on the effect of human disturbance on primate abundance and group size. The survey reveals the presence of the restricted-range red colobus, Procolobus gordonorum, in New Dabaga/Ulangambi Forest Reserve (NDUFR). The primate community of NDUFR is impoverished compared to that in Ndundulu forest. Red colobus and black-and-white colobus (Colobus angolensis palliatus) abundance and group size are lowest in NDUFR. Fission-fusion of red colobus social groups may be occurring in previously logged areas of both forests. Our observations are consistent with current theory on the effect of habitat degradation and hunting on primates, but the relative effects of the 2 factors could not be differentiated. We pooled the results with previous data to show that abundance of red colobus in the Udzungwa Mountains is lowest at high elevations. Low red colobus group sizes appear to be related to human activity rather than elevation. Black-and-white colobus and Sykes monkeys ( Cercopithecus mitis) show no relationship with elevation. Future studies will require more detailed information on vegetation, diet and ranging patterns to interpret fully intraspecific variation in population demography and social structure in the Udzungwa Mountains.

The mongoose family, Herpestidae, includes several species that comprise the most social small Carnivora. The small Indian mongooseHerpestes javanicus (E. Geoffroy Saint-Hilaire, 1818), a South Asian species that has been introduced to numerous Caribbean and Pacific islands, has not been reported to show complex sociality. A radio-tracking study conducted on Oahu, Hawaii, revealed that a group of at least 5, and perhaps more than 10, large males in the study area shared a single, large home range during the breeding season. Members of this group spent far more time than expected within 20 m of fellow members. Group members frequently shared dens, sleeping within 50 cm of each other. Females maintained very small, overlapping home ranges inside the male group’s range. Male breeding coalitions have previously been reported in a congeneric species, the slender mongooseHerpestes sanguineus.

Food availability is one of the basic factors affecting primate density and socioecology, but food availability is difficult to assess. Two different ways to obtain accurate estimates of food availability have been proposed: using phenology data or using the behaviour of animals. Phenology data can be refined by only including trees that are large enough to be used; including (potential) tree species in which by the concerned primate species forage; or including (fruiting) trees of these species that actually produce fruit. Alternatively, the sizes of the actually visited trees (foraging trees) give an estimate of fruit availability. These measures are compared for three sympatric primate species at the Ketambe Research Station, Sumatra, Indonesia: the Thomas langur, the long-tailed macaque and the orangutan. The sizes of fruiting trees and the foraging trees are larger than the potential trees. The sizes of the potential trees and of the fruiting trees are similar for the three primate species. This, however, is not reflected in the use of trees: the langurs forage on average in trees of similar size to those producing fruit, whereas the macaques and orangutans forage in trees larger than those producing fruit. The use of trees does not necessitate a different cut off point of included dbhs for the three compared primate species. The use of trees of different sizes, however, may be regulated by food competition. This indicates that sympatric primates make different foraging decisions and that behavioural measures of food availability will be less reliable.

Previous researchers of hamadryas baboons have described a star-shaped sociogram, whereby the strongest social bonds within hamadryas one-male units are between a leader male and his females and bonds among females are weak by comparison. This type of social organization is also known as cross-bonding to distinguish it from the female-bonding found in most papionin monkeys. Models of female primate socioecology suggest that hamadryas baboons lack female bonding due to their reliance on scarce, widely-dispersed food resources. Here, I report observational data from a wild population of hamadryas baboons in Ethiopia indicating that, while females varied widely in their frequency of social interaction with other females, most females spent about as much social time with other females as they did with the leader male and some females even crossed unit boundaries to interact with one another. The size of a unit was positively correlated with the tendency of its females to interact with other females and was negatively correlated with the tendency of its females to interact with the leader male. Females were equally likely to spend social time with other females whether or not the leader male was available for social interaction at the time. Overall, this study suggests that a star-shaped sociogram does not characterize all hamadryas baboons and that female hamadryas may be, to some extent, female-bonded as well as cross-bonded. The lack of more pronounced female bonding in hamadryas is probably due to the behavior of males rather than to ecological factors.

The social organization of the kinkajou Potos flavus is described from 380 h of observations on habituated, free-ranging animals. Individuals were most often alone while feeding at night, yet they regularly interacted in stable social groups. Four social groups were observed, each consisting of a single adult female, two adult males, one sub-adult and one juvenile. At least one breeding female was solitary and did not reside within a group. Social groups were consolidated primarily at denning sites and large fruiting trees by group feeding, allogrooming and scent marking. However, kinkajous were most often observed solitarily, as social feeding only occurred in 19.6 of total feeding bouts (mainly among males) and individuals rarely travelled together. Although the composition of social groups was polyandrous, males also copulated with non-group females which suggests a promiscuous mating system. Female-biased dispersal and patterns of male association seem to be patrilineal and based on resource defence. The evolution of social organization in the kinkajou is discussed in relation to predation risk, resource availability, and convergence with primates of similar fission–fusion socioecology.

Male and female Red-Backed Salamanders (Plethodon cinereus) establish territories under cover objects (rocks, logs) on forest floors of northeastern North America. Because females should be food limited and males mate limited in terms of fitness, we tested the hypothesis that territorial residents and invaders should differ intersexually in certain morphological or behavioral traits. We displaced males and females from cover objects on the forest floor at Mountain Lake Biological Station, Virginia, and monitored homing by displaced individuals and invasion of vacated cover objects by novel individuals. Neither residents nor invaders differed significantly intersexually in snout–vent lengths, total lengths, or sizes of cover objects inhabited. Also, the number of male versus female residents that successfully returned to their cover objects did not differ significantly. However, significantly more females than males invaded vacated cover objects, and they did so significantly faster. These data su...

Linnaeus' original scientific description of Lemur catta, the ringtailed lemur, was based on a living animal brought to England in 1749. Although there were many brief descriptions of wild ringtailed lemurs, it was not until Jolly wrote her now classic book, Lemur Behavior, that we had our first detailed description of the natural history of these beautiful animals (Fig. 1). Since then, long-term field studies, mainly from two study sites in Madagascar, Berenty and Beza Mahafaly (Fig. 2), as well as studies on forest-living groups in captivity at the Duke University Primate Center in Durham, North Carolina, have greatly expanded our knowledge of the ecology and behavior of this species (Table 1, Box 1). Thirty-five years of research on this species at these various sites indicates that Lemur catta is proving to be every bit as complex in its behavior as are many anthropoid primates. This very complexity has been reflected in the current controversies and questions concerning the ecology and behavior of this species.

Large-scale habitat destruction and poaching in the 1950s, 1960s, and 1970s had major impacts on the population size and demography of mountain gorillas (Gorilla beringei beringei) in Rwanda. In those three decades, the population of the Virunga Volcanoes was halved: groups became unstable, and infanticide was relatively common. Intensive conservation efforts began in the 1980s and have enabled the gorilla population to recover. The present study took place during a period of social stability in the lives of three Karisoke gorilla groups. Characterized by few female transfers, no known infanticide, and only one silverback male departure from the research groups, there were striking increases in both group size and the number of adult males per group. I consider how these changes have occurred and implications for the management of this Critically Endangered primate. Despite encouraging growth, this population is so small that it remains extremely vulnerable to human disturbance. If mountain gorillas are to survive in this volatile region, a hands-on approach to their conservation may be justified.

The African great apes live in such diverse habitats as lowland tropical forests, montane forests, and dry savannas, and they show great flexibility in their ecological and social features. To identify the factors causing variations in these features, we examined their ranging, grouping, and life history traits in relationship to their dietary preferences. Analysis of their dietary compositions shows that both gorillas and chimpanzees have strong preferences for ripe fruits but with different folivorous and faunivorous diets as their fallback strategies. Dietary variation mainly caused by fluctuation in fruit availability does not constrain group cohesion, but it affects the daily path length of gorillas and influences the party size and fluidity of chimpanzees. High gregariousness among female bonobos and western chimpanzees may be explained by their low feeding competition over supplementary food resources derived from the absence of the sympatric gorillas in their habitats. Although high association and linear hierarchy among female western chimpanzees are attributed to abundant and monopolizable fruit resources, the high female–male association observed in western chimpanzees and bonobos is not explained solely by ecological factors. The higher reliance on fruits leads to a slower life history for gorillas and a faster life history for chimpanzees. Male mating strategies have great influence on the sociality of the female African great apes. Infanticide by males may stimulate female gorillas to join multimale groups and promote rapid reproduction. By contrast, sexual coercion including infanticide by males may prevent female chimpanzees from forming a prolonged association with males, thus promoting slow reproduction. These observations imply that associations between ecological, behavioral, and social features have evolved in different ways with their different life history strategies between the genera Gorilla and Pan.

This chapter provides a basic introduction to the terminology and general concepts of primate behavior and ecology. It discusses the types of habitats primates occupy and their characteristics. Primate species differ in their patterns of land use, including home ranges and day ranges. Activity patterns describe whether a species in diurnal, nocturnal or cathemeral, and how much time is spent each day on different behaviors including feeding, travel, resting, and social behavior. Primates differ in their dietary habits, and show varying degrees of faunivory, frugivory, and folivory. Locomotor behavior includes arboreal quadrupedalism, terrestrial quadrupedalism, climbing, and bipedalism. Primates live in many different social structures, including monogamy, polyandry, single-male groups, multi-male groups, and fission-fusion societies. Patterns of social organization are the result of many factors, including food distribution, predation, and threat of infanticide. Primate life histories can be characterized along many different parameters.

Various ecological factors shape the structure and dynamics of primate societies, and many of these are increasingly being influenced by anthropogenic processes. The bonnet macaque Macaca radiata, endemic to peninsular India, usually lives in seasonal tropical deciduous forests and typically occurs in large multimale–multifemale associations. A particular population of this species in the Bandipur-Mudumalai wildlife sanctuaries of southern India, however, appears to have evolved, in recent years, a fairly high proportion of small, but reasonably stable, unimale troops with unique demographic and behavioral features. Food provisioning by tourists visiting these sanctuaries may have led to the evolution of this social organization, unique for a seasonally breeding cercopithecine primate. Provisioning also leads to a significant increase in aggressive competition among individuals within these groups for the newly available resources. Here, we explore how the simple act of feeding monkeys, an act considered virtuous by most Indians, has thus profoundly influenced the socioecology of this macaque population at two organizational levels, those of the society and the individual, and appears to undermine the survival of this population itself.

Considerations of primate behavioral evolution often proceed by assuming the ecological and competitive milieus of particular taxa via their relative exploitation of gross food types, such as fruits versus leaves. Although this “fruit/leaf dichotomy” has been repeatedly criticized, it continues to be implicitly invoked in discussions of primate socioecology and female social relationships, and explicitly invoked in models of brain evolution. An expanding literature suggests that such views have severely limited our knowledge of the social and ecological complexities of primate folivory. This paper examines the behavior of primate folivore-frugivores, with particular emphasis on gray langurs (traditionally, Semnopithecus entellus) within the broader context of evolutionary ecology. Although possessing morphological characters that have been associated with folivory and constrained activity patterns, gray langurs are known for remarkable plasticity in ecology and behavior. Their diets are generally quite broad and can be discussed in relation to “Liem’s paradox,” the odd coupling of anatomical feeding specializations with a generalist foraging strategy. Gray langurs, not coincidentally, inhabit arguably the widest range of habitats for a nonhuman primate, including high elevations in the Himalayas. They provide an excellent focal point for examining the assumptions and predictions of behavioral, socioecological, and cognitive evolutionary models. Contrary to the classical descriptions of the primate folivore, Himalayan and other gray langurs—and, in actuality, many leaf eating primates—range widely and engage in resource competition (both of which have previously been noted for primate folivores) as well as solve ecological problems rivaling those of more frugivorous primates (which has rarely been argued for primate folivores). It is maintained that questions of primate folivore adaptation, temperate primate adaptation, and primate evolution more generally cannot be answered by the frequent approach of broad characterizations, categorization models, crude variables, weakly correlative evidence, and subjective definitions. As a corollary, many current avenues of study are inadequate for explaining primate adaptation. A true understanding of primate ecology can only be achieved through the utilization of mainstream evolutionary ecology, and thorough linkage of both proximate and ultimate mechanisms.