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A Test of Foraging Models Using Dietary Diversity Indices for the Lomako Forest Bonobos
Abstract
Optimal diet and functional response models are used to understand the evolution of primate foraging strategies. The predictions of these models can be tested by examining the geographic and seasonal variation in dietary diversity. Dietary diversity is a useful tool that allows dietary comparisons across differing sampling locations and time periods. Bonobos ( Pan paniscus ) are considered primarily frugivorous and consume fruits, leaves, insects, vertebrates, terrestrial herbaceous vegetation, and flowers. Frugivores, like bonobos, are valuable for examining dietary diversity and testing foraging models because they eat a variety of species and are subject to seasonal shifts in fruit availability. Frugivorous primate species thus allow for tests of how variation in dietary diversity is correlated with variation in ecological factors. We investigated measures of dietary diversity in bonobos at two research camps across field seasons within the same protected area (N’dele and Iyema) in Lomako Forest, Democratic Republic of the Congo. We compared the results of behavioral observation (1984/1985, 1991, 1995, 2014, and 2017) and fecal washing analysis (2007 and 2009) between seasons and study period using three diversity indices (Shannon’s, Simpson’s, and SW evenness). The average yearly dietary diversity indices at N’dele were Shannon’s Hʹ = 2.04, Simpson’s D = 0.82, and SW evenness = 0.88 while at Iyema, the indices were Shannon’s Hʹ = 2.02, Simpson’s D = 0.82, and SW evenness = 0.88. Behavioral observation data sets yielded significantly higher dietary diversity indices than fecal washing data sets. We found that food item (fruit, leaf, and flower) consumption was not associated with seasonal food availability for the 2017 behavioral observation data set. Shannon’s index was lower during periods when fewer bonobo dietary items were available to consume and higher when fruit was abundant. Finally, we found that optimal diet models best-explained patterns of seasonal food availability and dietary diversity. Dietary diversity is an essential factor to consider when understanding primate diets and can be a tool in understanding variation in primate diets, particularly among frugivores. Dietary diversity varies across populations of the same species and across time, and it is critical in establishing a complete understanding of how primate diets change over time.
... Although not an exact proxy, the fecal microbiome reflects the trillions of microbes that reside in the gastrointestinal tract; microbes that collectively contribute to host digestion, immunity and pathogen defense, and intestinal barrier homeostasis [1]. While the composition of the fecal microbiome is highly dynamic and can correlate with a range of host factors including age [2,3], sex [4], body condition [5], diet [6,7], habitat [8,9], and antibiotic use [10], more persistent changes in composition have also been associated with disease and infections [11,12]. Compared to their healthy counterparts, the fecal microbiome of animals with the disease or infection may have reduced microbial diversity [13], decreased abundances of functionally important microbes like fermentative or short-chain fatty acid (SCFA)-producing bacteria [14], or elevated abundances of pathogenic taxa [15,16]. ...
There is growing interest in the application of fecal microbiota transplants (FMTs) in small animal medicine, but there are few published studies that have tested their effectiveness in the domestic cat (Felis catus). Here we use 16S rRNA gene sequencing to examine fecal microbiome changes in 68 domestic cats with chronic digestive issues that underwent FMT treatment using lyophilized stool that was delivered in oral capsules. Fecal samples were collected from FMT recipients before and two weeks after treatment, as well as from their stool donors, and healthy animals. We found that according to their owners, 77% of cats were reported to show improvement in their clinical signs (termed ‘Responders’), and 23% were reported to exhibit no change or a worsening of their clinical signs (termed ‘Non-Responders’). Variation in the fecal microbiomes of FMT recipients most strongly correlated with host clinical signs, diet, and IBD diagnosis. The relative abundances of Collinsella, Negativibacillus, Parabacteroides, and Peptoclostridium changed differentially in FMT recipients. Overall, on average 13% of the bacterial amplicon sequence variants (ASVs) were shared between stool donors and FMT recipients (excluding ASVs already present in FMT recipients prior to treatment). The most commonly shared ASVs were classified as Prevotella 9, Peptoclostridium, Bacteroides, Collinsella and unclassified Lachnospiraceae. Lastly, FMT recipients that had recently taken antibiotics exhibited increases in microbiome similarity to an age-matched healthy reference set compared to other cats. Cats that had diarrhea or diarrhea with vomiting became more similar to healthy cats than did cats exhibiting other clinical signs. Overall, our results suggest that oral capsule FMT treatment was effective in this group of cats and microbiome responses may be modulated by the FMT recipient’s initial presenting clinical signs, prior IBD diagnosis, recent antibiotic use, and their diet.
Selon les modèles socio-écologiques développés pour les primates non-humains, la disponibilité spatio-temporelle des ressources dans l’environnement a une influence importante sur leurs stratégies écologiques et sociales. La variabilité des stratégies de recherche de nourriture adoptées par les individus d'une même espèce dans des habitats différents écologiquement représente une source d’informations précieuse pour évaluer leur flexibilité. L’étude de cette flexibilité écologique et comportementale ainsi que des facteurs biotiques et abiotiques influençant les stratégies développées chez les espèces les plus proches de l’humain phylogénétiquement est essentielle pour améliorer notre compréhension des mécanismes évolutifs dans la lignée des hominidés (grands singes et humains ainsi que leurs ancêtres fossiles). Elle contribue également à optimiser les projets de conservation de ces espèces menacées d’extinction et à anticiper les réponses écologiques et comportementales des individus aux changements environnementaux liés aux activités anthropiques. De telles études sont nécessaires chez les bonobos (Pan paniscus) car cette espèce endémique de la République Démocratique du Congo et classée En danger d’extinction (IUCN) reste encore peu étudiée et la majorité des sites d'étude sont situés en forêt continue, limitant ainsi notre perception des différences intraspécifiques existantes. Cette étude avait donc pour objectif d’explorer les stratégies de recherche alimentaire des bonobos dans un habitat peu représenté dans leur aire de répartition (mosaïque forêt-savane), et dans un environnement offrant a priori une grande stabilité alimentaire (parc zoologique), en intégrant l’étape d’acquisition des aliments avant leur consommation à travers l’évaluation des capacités de manipulation de cette espèce. Nous avons ainsi développé une approche innovante et pluridisciplinaire associant dans un même projet des concepts et des méthodologies relevant de l’écologie fondamentale et de l’anatomie fonctionnelle. Cette étude nous a permis de montrer une grande amplitude de variation du régime alimentaire chez les bonobos, en fonction des ressources présentes dans leur environnement et de leur variabilité temporelle. En milieu naturel de mosaïque forêt-savane, malgré la sélection d’une grande diversité d’aliments, incluant des espèces de savane, certains d’entre eux prédominent périodiquement le régime (Dialium angolense notamment) et influencent alors l’utilisation de l’habitat. En parc zoologique, la consommation opportuniste d’espèces autochtones sélectionnées dans l’enclos représente une part importante du temps d’alimentation en complément de la ration quotidienne avec une variabilité saisonnière importante. Dans les deux milieux, lors de la saisie et de la manipulation des aliments, nous avons décrit pour la première fois un répertoire de postures manuelles et podales aussi large et diversifié que celui décrit chez le chimpanzé (Pan troglodytes). Les capacités morpho-fonctionnelles et cognitives sont donc similaires chez les deux espèces et ne suffisent pas à expliquer l’émergence de l’utilisation d’outils en milieu naturel, rare chez le bonobo. Cette étude a également permis de montrer que dans deux contextes écologiques aussi différents qu’une mosaïque forêt-savane et un parc zoologique, les comportements de manipulation exprimés pour parvenir à la consommation des ressources varient. La mise en évidence de cette variabilité intraspécifique pour les comportements manipulatoires et pour la sélection des ressources alimentaires est cohérente avec celle décrite chez le chimpanzé pour l’utilisation d’outils et plus généralement pour les stratégies de recherche alimentaire. Ces résultats enrichissent les connaissances sur cette espèce sous-représentée, confirment la flexibilité comportementale et écologique existant au sein du genre Pan dans son ensemble et contribuent à interroger les déterminants de cette variabilité intra et interspécifique.
La compréhension des facteurs de sélection et de préférence alimentaires représente un enjeu majeur pour la conservation des espèces in situ mais également ex situ puisqu’elle participe à l’amélioration du bien-être des individus hébergés en parc zoologique. Chez les bonobos (Pan paniscus), espèce endémique de la République Démocratique du Congo et classée en danger d’extinction par l’Union Internationale pour la Conservation de la Nature (UICN), ces facteurs de sélection sont peu connus. Les sites d’études en milieu naturel sont en effet peu nombreux et difficiles d’accès et les études sur ces problématiques en captivité sont rares. L’objectif de cette étude était donc de caractériser la prise alimentaire opportuniste d’une communauté de 17 bonobos hébergée au parc zoologique de la Vallée des Singes (Romagne, France) et ayant accès à un enclos extérieur de 0,8 hectares pourvu d’une végétation autochtone, afin d’en étudier les déterminants nutritionnels et écologiques. Grâce à une méthodologie pluri-disciplinaire associant observations comportementales individuelles, recensement botanique, analyses nutritionnelles (macro et micronutriments) et entretiens avec les soigneurs, cette étude réalisée sur trois saisons a révélé la consommation de 46 aliments appartenant à 26 espèces végétales avec une variabilité saisonnière importante. Les bonobos semblent en effet éviter les aliments les plus fibreux lorsque la disponibilité dans l’enclos le permet. Néanmoins, ces aliments demeurent plus riches en fibres que la ration et semblent apporter un complément alimentaire par rapport à la ration (fibres et calcium notamment), mais également un enrichissement comportemental, permettant une diminution des comportements anormaux de régurgitation-réingestion. Cette étude, complémentaire de celles menées en milieu naturel afin d’identifier les mécanismes de sélection des aliments, présente un intérêt majeur pour améliorer la nutrition et le bien-être des espèces hébergées.
There is growing interest in the application of fecal microbiota transplants (FMTs) in small animal medicine, but there are few published studies that have tested their effects in the domestic cat (Felis catus). Here we use 16S rRNA gene sequencing to examine fecal microbiome changes in 46 domestic cats with chronic digestive issues that received FMTs using lyophilized stool that was delivered in oral capsules. Fecal samples were collected from FMT recipients before and two weeks after the end of the full course of 50 capsules, as well as from their stool donors (N = 10), and other healthy cats (N = 113). The fecal microbiomes of FMT recipients varied with host clinical signs and dry kibble consumption, and shifts in the relative abundances of Clostridium, Collinsella, Megamonas, Desulfovibrio and Escherichia were observed after FMT. Overall, donors shared 13% of their bacterial amplicon sequence variants (ASVs) with FMT recipients and the most commonly shared ASVs were classified as Prevotella 9, Peptoclostridium, Bacteroides, and Collinsella. Lastly, the fecal microbiomes of cats with diarrhea became more similar to the microbiomes of age-matched and diet-matched healthy cats compared to cats with constipation. Overall, our results suggest that microbiome responses to FMT may be modulated by the FMT recipient’s initial presenting clinical signs, diet, and their donor’s microbiome.
Recent advances in niche theory have stressed the importance of understanding dietary generalism at multiple levels, including the range of habitat and foods exploited by a species, foods exploited within populations, and patterns of nutrient intake. Here we apply this framework to examine the dietary strategy of the Macaca mulatta, a primate species that is second only to humans in their breadth of geographical distribution, and occupy diverse ecological habitats from cold temperate to tropical latitudes. A recent study showed that the Taihangshan subspecies ( M. mulatta tcheliensis) in China, which is found at the northern latitudinal limit of the species range, respond to ecologically constrained interannual variation in the macronutrient ratios of the spring diet in a way that theory predicts should be associated with ecological generalism. Here we further extend this study, examining the relationships between seasonal variation in food availability and the patterns of food selection across a full year. We found that, despite the ecological and macronutritional generalism of the species, Taihangshan macaques subsist on a relatively small range of foods (57 different foods, spread across 8 categories comprising seeds, fruits, buds, flowers, leaves, herbs, young bark, and twigs), but face considerable seasonal variation in the combinations available. In spring and summer, when seeds were scarce, leaves accounted for 60.3 ± 13.8% of their diet (dry matter [DM] %), and herbs contributed 31.7 ± 22.2%. However, in autumn and winter, when seeds were abundant, they contributed 68.5 ± 22.7% of the diet while herbs accounted for 18.9 ± 12.9% on a DM. Although young bark and twigs were available in all seasons, the macaques only fed on them in winter. We present comparative data from the literature on the diets of M. mulatta and other Macaca species, to interpret this pattern of resource use within the framework of multilevel niche theory.
Dietary data are used to categorize species diets, but these categorizations do not take into account the mutability of food resources in time or space, the level of interspecific competition in various communities as these resources change, nor the dietary flexibility of species. In this study, we assess the diets of three sympatric species, Eulemur rufifrons, Propithecus edwardsi, and Varecia variegata, in the Vatoharanana site in Ranomafana National Park, Madagascar. We determine dietary diversity, overlap, and interannual variation with data collected from 2001 to 2003. We then compare results on food preference and time feeding with data collected on each species in the late 1980s and early 1990s to determine whether these findings are consistent over the long term. We found little interannual variation in the proportion of time spent eating particular plant parts for each of the lemur species during the three study years (2001–2003), and between the earlier and current study. Food items were not always consumed based solely on availability. Dietary diversity was lower in the two frugivorous species (V. variegata and E. rufifrons) compared with the folivorous species (P. edwardsi), and V. variegata and E. rufifrons were more likely to focus their feeding time on one particular genus and plant part in each year. The study species used different strategies to deal with food, particularly fruit, shortages such as a plastic social structure (V. variegata), habitat shifting (E. rufifrons), and dietary switching (P. edwardsi). Although there was low dietary overlap between the study species, they depended on a small number of shared fruits in each of the study years (Chrysophyllum, Syzygium, Ocotea, Plagioscyphus), which may indicate some potential for interspecific competition. Because these lemur species, like all primates, lead relatively long lives (avg. >30 years) and have slow rates of aging, longitudinal studies are needed to test hypotheses reliant on basic dietary information. © 2018 Springer Science+Business Media, LLC, part of Springer Nature
Evolutionary models consider hunting and food sharing to be milestones that paved the way from primate to human societies. Because fossil evidence is scarce, hominoid primates serve as referential models to assess our common ancestors' capacity in terms of communal use of resources, food sharing, and other forms of cooperation. Whereas chimpanzees form male-male bonds exhibiting resource-defense polygyny with intolerance and aggression toward nonresidents, bonobos form male-female and female-female bonds resulting in relaxed relations with neighboring groups. Here we report the first known case of meat sharing between members of two bonobo communities, revealing a new dimension of social tolerance in this species. This observation testifies to the behavioral plasticity that exists in the two Pan species and contributes to scenarios concerning the traits of the last common ancestor of Pan and Homo. It also contributes to the discussion of physiological triggers of in-group/out-group behavior and allows reconsideration of the emergence of social norms in prehuman societies.
Research on wild apes is not only fundamental for elucidating human origins but for their conservation as well. Despite their relative size, apes are difficult to observe in the wild prior to habituation, limiting our ability to accurately assess demography and kin relations. Non-invasive genetic sampling provides an indirect source of this information. Here, we present findings of a pilot genetic survey of a wild community of bonobos that are in the initial stages of being studied. Fifty-three fecal samples were collected over eight days near the Iyema field site in the Lomako Forest, DRC. DNA was first extracted and quantified using a qPCR assay. Samples with a sufficient amount of DNA were genotyped at 11 microsatellite loci and sexed using an amelogenin assay. Thirty-three of 53 samples yielded a sufficient amount of DNA for complete genotyping. We identified 19 individuals, including six males and 13 females. Mean allelic richness across all loci was 5.7 and expected heterozygosity was 0.69. Estimates of population size indicate between 26 and 66 individuals are present in the study area, but more than one community may be present. These results contribute to our ongoing efforts to study and monitor the bonobos at Iyema to better understand their demography, behavior, and conservation. Our study also highlights the utility of genetic analyses in pilot and survey research.
Eating is a risky affair. All animals have to offset risks of feeding such as exposure to plant toxins, increased vulnerability to predation, or conspecific aggression with a food's energetic and nutritional return. What, when, and where an individual eats can impact fitness and, ultimately, species-level adaptations. Here, we explore the variables that influence primate feeding preference: food availability, chemical defense, and nutrient content. We present information demonstrating that consumers manipulate nutrient and energy intake, indicating that what may be a less-than-optimal food for one state of an animal's phenotype may not be for another. This evidence suggests that factors previously assumed to be constraints in Optimal Foraging Theory, Functional Response, and-recently-Fallback Food feeding models would be better categorized as variables. We conclude that "fallback" is not an intrinsic state of the food or the consumer and that this conclusion complicates the application of this concept to morphological features in the fossil record.
The composition of the diet of a savanna-living population of wild chimpanzees (Pan troglodytes verus) at Mt. Assirik in Senegal is presented. The study site had a prolonged dry season, high temperatures, and vegetation dominated by grasses. Data came from direct observation, fecal specimens, and feeding traces; thus, strict criteria for acceptance of the indirect data were specified. Composition of diet was given in terms of species and family of prey, parts eaten, life-form, type of habitat, and criteria for inclusion. Forty-three species of plants with 60 parts were eaten; mostly fruits, from trees, in woodland. Nine species of animal prey were eaten, mostly social insects. An additional 41 species of plants with 53 parts were classed as likely to be eaten by chimpanzees, mostly on the grounds of their being eaten by sympatric anthropoids. Overall, the diet of the apes at Mt. Assirik resembles that of this species elsewhere in Africa, but the size of the dietary repertoire seems small and the proportion of low-quality foodstuffs high. The latter are mostly time-consuming to collect or tedious to obtain or process, and include underground storage organs.
Macroscopic inspection of feces has been used to investigate primate diet. The limitations of this method to identify food-items to species level have long been recognized, but ascertaining aspects of diet (e.g., folivory) are achievable by quantifying food-items in feces. Quantification methods applied include rating food-items using a scale of abundance, estimating their percentage volume, and weighing food-items. However, verification as to whether or not composition data differ, depending on which quantification method is used during macroscopic inspection, has not been done. We analyzed feces collected from ten adult chimpanzees (Pan troglodytes schweinfurthii) of the Kanyawara community in Kibale National Park, Uganda. We compare dietary composition totals obtained from using different quantification methods and ascertain if sieve mesh size influences totals calculated. Finally, this study validates findings from direct observation of feeding by the same individuals from whom the fecal samples had been collected. Contrasting diet composition totals obtained by using different quantification methods and sieve mesh sizes can influence folivory and frugivory estimates. However, our findings were based on the assumption that fibrous matter contained pith and leaf fragments only, which remains to be verified. We advocate macroscopic inspection of feces can be a valuable tool to provide a generalized overview of dietary composition for primate populations. As most populations remain unhabituated, scrutinizing and validating indirect measures are important if they are to be applied to further understand inter- and intra-species dietary variation. Am. J. Primatol. © 2014 Wiley Periodicals, Inc.
We review studies that consider how food affects primate population abundance. In order to explain spatial variation in primate abundance, various correlates that parameterize quality and quantity of food in the habitat have been examined. We propose two hypotheses concerning how resource availability and its seasonality determine animal abundance. When the quality of fallback foods (foods eaten during the scarcity of preferred foods) is too low to satisfy nutritional requirement, total annual food quantity should determine population size, but this relationship can be modified by the quality or the quantity of fallback foods. This mechanism has been established for Japanese macaques and sportive lemurs that survive lean seasons by fat storage or extremely low metabolism. Second, when fallback food quality is high enough to satisfy nutritional requirement but quantity is limited, quantity of fallback food should be a limiting factor of animal abundance. This is supported by the correlation between fig density, which is a high-quality fallback food, and gibbon and orangutan abundance. For a direct test of these hypotheses, we need more research that determines both the quality of food that animals require to satisfy their nutritional requirement and the quantity of food production. Leaves are often regarded as superabundant, but this assumption needs careful examination.
An important goal of primatology is to identify the ecological factors that affect primate abundance, diversity, demography, and social behavior. Understanding the nutritional needs of primates is central to understanding primate ecology because adequate nutrition is a prerequisite for successful reproduction. Here, we review nutritional methods and provide practical guidelines to measure nutrient intake by primates in field settings. We begin with an assessment of how to estimate food intake by primates using behavioral observations. We then describe how to collect, prepare, and preserve food samples. Finally, we suggest appropriate nutritional assays for estimating diet nutritional quality and point to the merits and limitations of each. We hope this review will inspire primatologists to use nutritional ecology to answer many unresolved questions in primatology.
In this 3-year investigation we documented patterns of density, diet, and activity of red colobus monkeys (Procolobus tephrosceles) in six areas in or near Kibale National Park, Uganda and related these patterns to availability of food resources. There were large differences in the density and behavior of the red colobus among the sites. For example, the red colobus at one site with a diverse plant community of more than 61 tree species, had a diet that included at least 42 species. In contrast, at a second site red colobus spent 92% of their feeding time eating from one species that dominated the tree community. The density of important red colobus food trees varied among sites from 32 trees/ha to 204 trees/ha, and red colobus density ranged from 0.70 groups/km(2) to 7.41 groups/km(2). Among sites, red colobus density was related to the cumulative DBH of important food trees, when one apparently anomalous site was excluded, and populations with more plant species in their diets tended to be those that were found at higher densities. Activity budgets of the red colobus populations varied markedly among sites. For example, feeding time ranged among sites from 29 to 55%, and traveling varied from 5 to 20%. When faced with increased foraging demands, red colobus reduced the time spent resting, while the time spent socializing remained fairly constant. Comparative socioecological studies typically contrast species separated by large geographical distances to ensure there is sufficient variation in the environment to detect behavioral responses. The marked differences in ecological conditions and red colobus behavior we documented over short geographical distances, suggests that small-scale contrasts are a useful tool to examine ecological determinants of behavior and community structure.
Chimpanzee diets are highly variable, but in all cases dominated by ripe fruit. Previous work has suggested that in the Budongo Forest Reserve, Uganda, ripe fruit remains available throughout the year, but dietary data for chimpanzees at this site remain sparse. This paper details the diet of a recently habituated community of Budongo chimpanzees living in the Sonso region. Chimpanzees of this community spent 64.5% of their feeding time eating fruit, and 19.7% eating arboreal leaves. Terrestrial herbaceous vegetation formed only a minor component of the diet. In these general dietary characteristics, Budongo chimpanzees show greater similarity to those of the Gombe National Park than they do to those in the geographically closer and floristically more similar Kibale Forest National Park. The diet was dominated by the fruit of four species and leaves of two species, although the composition of the diet varied from month to month, remaining diverse. Figs were consumed throughout much of the year, and in consequence, should perhaps be regarded as a staple, rather than fallback, food. A period of food scarcity was not apparent in this study and future comparative nutritional investigation will be required to determine whether these chimpanzees face a time of dietary hardship.
Food is vital for life. It provides nutrients for growth, maintenance, and reproduction, and is the source of energy that drives the chemical reactions occurring in every cell.1,2 However, most food, as it is initially procured, is not in a form suitable for use; it must first be broken down so that it can be transported through cell membranes.1 The breaking down of food molecules via a system of both mechanical and chemical processes so that they are of use to the body is called digestion.2,3 © 1998 Wiley-Liss, Inc.
Aim To analyse the biogeographical patterns in the feeding habits and trophic diversity of prey of the wildcat, Felis silvestris Schreber.
Location The Eurasian distribution range from the Caucasian mountains to the Iberian Peninsula and Scotland.
Methods We reviewed 15 studies to collate data on feeding behaviour across the current wildcat distribution range. We considered nine prey groups and recorded the latitude, whether the location was within a Mediterranean bioclimate area, and rabbit presence. Prey groups were reduced into four PCA factors. Regression analyses were performed to examine the relationships of latitude with PCA factors and trophic diversity. anova was used to test if trophic diversity was higher at locations with Mediterranean climates. We also analysed the relationship between small rodent consumption and both Mediterranean climates and rabbit presence using anova . Finally, we confirmed the relationship between the frequency of Murinae and Microtinae in the diets and the presence of rabbits and with respect to Mediterranean climates controlling for latitude ( mancova ).
Results Diet diversity was greatest in Mediterranean climates. Trophic diversity decreased when rodents formed the bulk of the diet, but increased with the inclusion of alternative prey such as rabbits and invertebrates. Small rodent consumption was also negatively related to rabbit consumption or presence. The inclusion of Murinae and Microtinae in the diet varied with latitude, with higher ingestion of the former in the southern locations and of the latter in northern areas.
Main conclusions The trophic diversity of the wildcat diet was associated with Mediterranean climatic conditions, being broader at more southern latitudes. At the continental scale, the wildcat cannot be considered a rodent specialist because rabbits were preferred when they were present. Thus, we consider the wildcat to be a facultative specialist. In addition, our results indicate that general trophic patterns in the diet of a species may not be accurately determined if the availability of alternative prey is not taken into account.
We studied seasonal change in habitat use by chimpanzees in the Kalinzu Forest, Uganda. The forest comprises various types of vegetation. For each vegetation type, we compared number of chimpanzees (per km2) that used the vegetation with fruit availability in different census periods. We estimated the number of chimpanzees by nest count and fruit availability via density of fallen fruit. The mixed mature forest contained a large amount of fruit during the high-fruiting season, but it decreased rapidly in the low-fruiting season. The number of chimpanzees also decreased in mixed mature forest in approximate proportion with fruit availability. In the Parinari-dominated mature and secondary forests, both fruit availability and number of chimpanzees were very low throughout the study. In the Musanga-dominated secondary forest, the number of chimpanzees increased toward the low-fruiting season, though the fruit availability decreased slightly. A multiple regression analysis showed that various fruits had significant effects on the number of chimpanzees during the high-fruiting season, while only Musanga
leo-errerae had a significant effect during the low-fruiting season. The results suggest that the fruit of Musanga leo-errerae functions as a fallback food, and a combination of different vegetation types supports the chimpanzees in the Kalinzu Forest.
Dietary data have been used to address numerous theoretical issues, yet we have little understanding of dietary flexibility
in primates. Previous comparative research has either explicitly or implicitly assumed that the closer the phylogenetic proximity
between two taxa, or the spatial proximity between two populations of the same taxon, the more similar their diets will be.
We examine such assumptions by making dietary comparisons among arboreal Cercopithecus species at the intergroup, interdemic, interpopulational, and interspecific levels. Our analyses reveal considerable variation
and sometimes the magnitude of the variation of particular contrasts is unexpected. We conclude that dietary flexibility blurs
our traditional trophic assessment of primate species. Thus, a study of the diet of a single group, in a specific habitat,
at one point in time may not be representative of the species as a whole. This flexibility suggests that a profitable avenue
of future research is quantifying the degree of flexibility that different primate lineages have in their digestive strategies.
Within this evolutionary framework, we can reasonably assume that feeding-related features observed in extant primates should be, at least in theory, demonstrably the result of natural selection. It is the demonstrable aspect of this important assumption that those concerned with dietary adaptations in the present and in the evolutionary past must confront. In addition to information derived from morphology, it is a truism that scientists studying extant primates have the luxury of observing the function of diet-related anatomy via direct observation of a feeding animal, while those scientists evaluating fossil species do so in the absence of such data (Kay, 1984). Yet, both scientists confront a similar challenge, and in evolutionary terms yield comparably synchronic interpretations; the ghost of selection past haunts us all. Hence, our use of the powerful combination of comparative models, extant species analogs, and correlative evaluations as tools for interpreting changes in form and function over evolutionary time.
Lemurs, lorises, and tarsiers are socially and ecologically diverse primates that include some of the most endangered mammals. We review results of long-term studies of 15 lemur species from 7 sites in Madagascar and 1 species each of loris and tarsier in Indonesia. We emphasize that the existence of long-term study populations is a crucial prerequisite for planning and conducting shorter studies on specific topics, as exemplified by various ecophysiological studies of lemurs. Extended studies of known individuals have revealed variation in social organization within and between ecologically similar species. Even for these primates with relatively fast life histories, it required more than a decade of paternity data to characterize male reproductive skew. The long-term consequences of female rank on reproductive success remain poorly known, however. Long-term monitoring of known individuals is the only method to obtain data on life-history adaptations, which appear to be shaped by predation in the species covered here; long-term studies are also needed for addressing particular questions in community ecology. The mere presence of long-term projects has a positive effect on the protection of study sites, and they generate unique data that are fundamental to conservation measures, such as close monitoring of populations.
Los lémures, lorises y tarseros son grupos de primates, muy diversos social y ecológicamente, que incluyen algunas de las especies de mamíferos más amenazadas. Se revisaron los resultados de estudios a largo plazo de 15 especies de lémures en 7 áreas de estudio en Madagascar y una especie de loris y otra de tarsero, en Indonesia. Se resalta la importancia de las áreas de estudio a largo plazo como prerrequisito esencial para planear y llevar a cabo estudios de menor duración sobre temas especificos, como lo ejemplifican varios estudios eco-fisiológicos en lemurs. Estudios a largo plazo de individuos conocidos, han revelado variacion en la organizacion social dentro y entre especies ecologicamente similares. Incluso en estos primates, con un ciclo de vida relativamente corto, se necesita recopilar más de una década de datos de paternidad para determinar el sesgo reproductivo de los machos. Sin embargo, aún se sabe poco de las consecuencias a largo plazo que la posición de las hembras en la jerarquía social puede tener en su éxito reproductivo. El monitoreo a largo plazo de individuos conocidos es el unico metodo para obtener datos sobre adaptaciones en su history natural, las cuales aparentemente son moduladas en function de la predacion a las especies estudiadas en este trabajo. Estos estudios a largo plazo son tambien necesarios para afrontar temas específicos sobre la ecología de estas comunidades. La simple presencia de proyectos a largo plazo tienen un efecto positive en la proteccion de los lugares de studio, como asi tambien generan datos unicos que son fundamentals para apoyar medidas de conservacion tales como el monitoreo de poblaciones.
The great apes (chimpanzees, bonobos, gorillas and orangutans) are our closest living relatives, sharing a common ancestor only five million years ago. We also share key features such as high intelligence, omnivorous diets, prolonged child-rearing and rich social lives. The great apes show a surprising diversity of adaptations, particularly in social life, ranging from the solitary life of orangutans, through patriarchy in gorillas to complex but different social organisations in bonobos and chimpanzees. As great apes are so close to humans, comparisons yield essential knowledge for modelling human evolutionary origins. Great Ape Societies provides comprehensive up-to-date syntheses of work on all four species, drawing on decades of international field work, zoo and laboratory studies. It will be essential reading for students and researchers in primatology, anthropology, psychology and human evolution.
Primate behavioral ecology is a subfield of primatology that employs evolutionary and ecological approaches to investigate the behavior of living primates. The approach is predicated on the assumption that behavioral traits, similar to morphological and physiological traits, are shaped by evolutionary selection pressures because of the differential fitness benefits they confer on individuals. Many features of primate social organization can be explained by the resulting behavioral strategies, which differ for females and males because of the sex differences in reproductive potential. New challenges include identifying facultative responses to the altered ecological and demographic conditions under which many primates now live and incorporating intraspecific behavioral variation into predictive, phylogenetically controlled models of social evolution.
Objectives:
Primates have an extended period of juvenility before adulthood. Although dietary complexity plays a prominent role in hypotheses regarding the evolution of extended juvenility, the development of feeding behavior is still poorly understood. Indeed, few studies have investigated the timing and nature of feeding transitions in apes, including chimpanzees. We describe general patterns of feeding development in wild chimpanzees and evaluate predictions of the needing-to-learn hypothesis.
Materials and methods:
We analyzed 4 years of behavioral data (2010-2013) from 26 immature chimpanzees and 31 adult chimpanzees of the Kanyawara community in Kibale National Park, Uganda. Specifically, we examined milestones of nutritional independence (first consumption of solid food and cessation of suckling) as well as developmental changes in feeding time, diet composition, diet breadth, and ingestion rates.
Results:
Chimpanzees first fed on solid food at 5.1 months and, on average, suckled until 4.8 years. Daily feeding time of immature individuals reached adult levels between 4 and 6 years, while diet composition showed minor changes with age. By juvenility (5-10 years), individuals had a complete adult diet breadth. Ingestion rates for five ripe fruit species remained below adult levels until juvenility but continued to show absolute increases into adolescence.
Discussion:
Chimpanzees acquired adult-like patterns on all feeding measures by infancy or juvenility. These data are inconsistent with the needing-to-learn hypothesis; moreover, where delays exist, alternatives hypotheses make similar predictions but implicate physical constraints rather than learning as causal factors. We outline predictions for how future studies might distinguish between hypotheses for the evolution of extended juvenility.
Three markedly different models of multispecies competition—one mechanistic, one phenomenological, and one statistical—all predict that greater diversity increases the temporal stability of the entire community, decreases the temporal stability of individual populations, and increases community productivity. We define temporal stability as the ratio of mean abundance to its standard deviation. Interestingly, the temporal stability of entire communities is predicted to increase fairly linearly, without clear saturation, as diversity increases. Species composition is predicted to be as important as diversity in affecting community stability and productivity. The greater temporal stability of more diverse communities is caused by higher productivity at higher diversity (the “overyielding” effect), competitive interactions (the “covariance” effect), and statistical averaging (the “portfolio” effect). The relative contribution of each cause of temporal stability changes as diversity increases, but the net effect is that greater diversity stabilizes the community even though it destabilizes individual populations. This theory agrees with recent experiments and provides a degree of resolution to the diversity‐stability debate: both sides of the longstanding debate were correct, but one addressed population stability and the other addressed community stability.
The isotope ecology of great apes is a useful reference for palaeodietary reconstructions in fossil hominins. As extant apes live in C3-dominated habitats, variation in isotope signatures is assumed to be low compared to hominoids exploiting C4-plant resources. However, isotopic differences between sites and between and within individuals are poorly understood due to the lack of vegetation baseline data. In this comparative study, we included all species of free-ranging African great apes (Pan troglodytes, Pan paniscus, Gorilla sp.). First, we explore differences in isotope baselines across different habitats and whether isotopic signatures in apes can be related to feeding niches (faunivory and folivory). Secondly, we illustrate how stable isotopic variations within African ape populations compare to other extant and extinct primates and discuss possible implications for dietary flexibility. Using 701 carbon and nitrogen isotope data points resulting from 148 sectioned hair samples and an additional collection of 189 fruit samples, we compare six different great ape sites. We investigate the relationship between vegetation baselines and climatic variables, and subsequently correct great ape isotope data to a standardized plant baseline from the respective sites. We obtained temporal isotopic profiles of individual animals by sectioning hair along its growth trajectory. Isotopic signatures of great apes differed between sites, mainly as vegetation isotope baselines were correlated with site-specific climatic conditions. We show that controlling for plant isotopic characteristics at a given site is essential for faunal data interpretation. While accounting for plant baseline effects, we found distinct isotopic profiles for each great ape population. Based on evidence from habituated groups and sympatric great ape species, these differences could possibly be related to faunivory and folivory. Dietary flexibility in apes varied, but temporal variation was overall lower than in fossil hominins and extant baboons, shifting from C3 to C4-resources, providing new perspectives on comparisons between extinct and extant primates.
Chimpanzees (Pan troglodytes) and bonobos (P. paniscus) are our closest living relatives, with the human lineage diverging from the Pan lineage only around five to seven Mya, but possibly as early as eight Mya.1–2 Chimpanzees and bonobos even share genetic similarities with humans that they do not share with each other.2 Given their close genetic relationship to humans, both Pan species represent crucial living models for reconstructing our last common ancestor (LCA) and identifying uniquely human features. Comparing the similarities and differences of the two Pan is thus essential for constructing balanced models of human evolution.3
In recent years, intensive field studies on pygmy chimpanzees (Pan paniscus), have been carried out in at least four localities within their range in the Zaire (Congo) forest: Wamba, Lomako, Lake Tumba, and Yalosidi (Fig. 1). Of these four localities, reports from study sites other than Wamba have centered around the ecology of pygmy chimpanzees [e.g., Badrian and Badrian (1977) and Badrian et al. (1981) from Lomako; Horn (1980) from Tumba; Kano (1983) from Yalosidi]. At Wamba, field studies have been in progress since 1974, focusing on behavior (Kuroda, 1980, and this volume; Kano, 1980, 1982a, b, and 1984) and social organization (Kuroda, 1979; Kano, 1982a; Kitamura, 1983), with ecology a secondary concern.
Chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), otherwise known as pygmy chimpanzees, are the only two species of the genus Pan. As they are our nearest relatives, there has been much research devoted to investigating the similarities and differences between them. This book offers an extensive review of the most recent observations to come from field studies on the diversity of Pan social behaviour, with contributions from many of the world's leading experts in this field. A wide range of social behaviours is discussed including tool use, hunting, reproductive strategies and conflict management as well as demographic variables and ecological constraints. In addition to interspecies behavioural diversity, this text describes exciting new research into variations between different populations of the same species. Researchers and students working in the fields of primatology, anthropology and zoology will find this a fascinating read.
Primates along with many other animal taxa are forced to cope with large shifts in basic ecological conditions because of rapid anthropogenically induced changes of their habitats. One of the coping strategies for primates is to adjust their diet to these changes, and several studies have demonstrated the importance of fallback resources for this. Bonobos, like chimpanzees, might be particularly vulnerable to habitat fragmentation because of their high dependence on fruit availability. Little is known, however, about bonobo feeding ecology in fragmented habitats and their use of fallback resources. In this study, we investigate diet seasonal variation and the exploitation of preferred and fallback foods in a bonobo population living in forest-savannah mosaics. Results show that bonobos have adapted to this fragmented habitat by feeding on only a few fruit species, including an important number of non-tree species (liana, herb and savannah shrub), in comparison to populations living in dense forests. These non-tree plants have been defined as fallback and non-preferred foods, which are most probably consumed to maintain high frugivory. Interestingly, we identified that preferred foods are all typical of mature forests while fallback resources are mainly found in forest edges or disturbed areas. This finding indicates that bonobos prefer to use mature forests when feeding, as they do for nesting, but extend their range use to forest areas in close proximity to humans when the availability of preferred fruits is low. Finally, we show that bonobo diet relies heavily on two abundant fallback fruits: Musanga cecropioides and Marantochloa leucantha. Other studies have demonstrated that the selection of abundant fallback resources enables primates to subsist at high densities and to maintain cohesive groups, as observed at this study site. Our findings suggest that bonobos living in forest-savannah mosaics can be considered as staple fallback food consumers. Am. J. Primatol. © 2015 Wiley Periodicals, Inc.
© 2015 Wiley Periodicals, Inc.
The assessment of fruit abundance is critical for studies of frugivore ecology A variety of methods have been used to estimate habitat-wide fruit abundance. However, since the methods have not been calibrated with each other, it is difficult to compare results of different studies. Here we compare three methods used simultaneously to collect fruit abundance data in the Kibale Forest, Uganda. Estimates of fruit abundance derived from fruit traps were not correlated with estimates derived from either systematic transect sampling or estimates obtained from observing fruiting phenology of key species on a fruit trail. However, estimates based on fruit trail data and transect data were correlated. We review the advantages and disadvantages of methods that have been used to assess habitat-wide fruit abundance.
The black-faced black spider monkey, Ateles paniscus chamek, was studied at Cocha Cashu, Manu National Park, Peru, from June to August 1982. The density of independently locomoting individuals was found to be 31/km2, and the average party size was 3.15. Data on age and sex compositions of parties, activity patterns, and diet composition are presented. The spider monkeys spend approximately 30% of observed time feeding, 44% resting, and 25% moving. They ate 80% fruit and 17% new leaves. Spider monkeys appear to be important seed dispersers. The best dispersal observed was for fruits with few, relatively large seeds. A rough day-range of 2,400 m was estimated from measured travel times and distances. The social system of Ateles is discussed.
Over an eight-year period, a total of 174 food items were recorded for chimpanzees (Pan t. troglodytes) in the Lopé Reserve in central Gabon. Plant foods, principally fruit, dominated the diet but insects were eaten regularly, and predation on at least three species of mammal occurred infrequently. The diversity of the vegetative component of the diet (leaves, stems, and bark) was probably underestimated by fecal analysis. Comparison of chimpanzee diet at Lopé with that of sympatric lowland gorillas showed the majority of foods were eaten by both species (73% of chimpanzee food items and 57% of gorilla food items). The overlap of fruit species was greater (82% and 79%, respectively) than that of other food classes. Both chimpanzees and gorillas harvested the majority of their plant foods arboreally (76% and 69%, respectively). The high degree of dietary overlap suggested that ecological competition between these two closely related species might exist. Few overt signs of competition for food either between or within species were observed but when fruit was scarce, the diets of the two species showed greatest divergence. The major differences between chimpanzee and gorilla diet at Lopé were the larger quantities of vegetative foods regularly eaten by gorillas and their ability to resort to a diet dominated by vegetative foods when fruit was scarce. In these respects, chimpanzees at Lopé resembled populations of Pan troglodytes studied elsewhere while Lopé gorillas resembled mountain gorillas (Gorilla g. beringei) and bonobos (Pan paniscus) in their greater dependence on vegetative foods. © 1993 Wiley-Liss, Inc.
Many types of biological studies require the estimation of food abundance in tropical forests, and a variety of methods have been used to estimate this parameter. Here we compare the accuracy and precision of three methods for estimating the fruit abundance (biomass and number) of tropical tree species: tree diameter, crown volume, and visual estimation. Diameter at breast height (DBH) was the most consistently accurate method and exhibited low levels of interobserver variability. Generally, crown volume was neither precise nor accurate. The visual estimation method was accurate for trees with very large fruit, but exhibited high interobserver variability.
Summary • The science of nutritional ecology spans a wide range of fields, including ecology, nutrition, behaviour, morphology, physiology, life history and evolutionary biology. But does nutritional ecology have a unique theoretical framework and research program and thus qualify as a field of research in its own right? • We suggest that the distinctive feature of nutritional ecology is its integrative nature, and that the field would benefit from more attention to formalizing a theoretical and quantitative framework for developing this. • Such a framework, we propose, should satisfy three minimal requirements: it should be nutritionally explicit, organismally explicit, and ecologically explicit. • We evaluate against these criteria four existing frameworks (Optimal Foraging Theory, Classical Insect Nutritional Ecology, the Geometric Framework for nutrition, and Ecological Stoichiometry), and conclude that each needs development with respect to at least one criterion. • We end with an initial attempt at assessing the expansion of our own contribution, the Geometric Framework, to better satisfy the criterion of ecological explicitness.
Attempts to relate interspecific differences in social organisation
among primates to gross differences in habitat or diet type have been
largely unsuccessful. This is probably partly because distantly related
species have adapted to similar ecological situations in different ways
and partly because much finer ecological differences are important.
The relative importance of feeding competition in Pan paniscus and Pan troglodytes schweinfurthii is examined in an attempt to understand the major differences in social organization of the two species. P. paniscus at Lomako is characterized by a stronger tendency for association among females than among female P. troglodytes at Gombe. Party size in P. paniscus is dependent on patch size. Feeding competition was more important in small patches than in large patches. The total amount of feeding time by a party in a patch (chimp-minutes) was a measure of patch size that was available for both chimpanzee species. P. paniscus was found to have larger party sizes and to use larger food patches than P. troglodytes. The importance of dispersed ground foods for each species of chimpanzee was compared and, although the results are not conclusive, they indicate that this type of food was equally important in the diets of both populations. Two hypotheses of the ecological basis for differences in social structure are compared in light of this evidence.
Primates tend to prefer specific plant foods, and primate home ranges may contain only a subset of food species present in an area. Thus, primate feeding strategies should be sensitive to the phenology of specific species encountered within the home range in addition to responding to larger scale phenomena such as seasonal changes in rainfall or temperature. We studied three groups of Javan gibbons (Hylobates moloch) in the Gunung Halimun-Salak National Park, Indonesia from April 2008 to March 2009 and used general linear mixed models (GLMM) and a model selection procedure to investigate the effects of variation in fruit and flower availability on gibbon behavior. Preferred foods were defined as foods that are overselected relative to their abundance, while important food species were those that comprised >5% of feeding time. All important species were also preferred. Season and measurements of flower and fruit availability affected fruit-feeding time, daily path lengths (DPL), and dietary breadth. Models that included the availability of preferred foods as independent variables generally showed better explanatory power than models that used overall fruit or flower availability. For one group, fruit and preferred fruit abundance had the strongest effects on diets and DPL in the models selected, while another group was more responsive to changes in flower availability. Temporal variation in plant part consumption was not correlated in neighboring groups. Our results suggest that fine-scale local factors are important determinants of gibbon foraging strategies. Am. J. Primatol. 00:1-14, 2012. © 2012 Wiley Periodicals, Inc.
In an earlier study (Holling, 1959) the basic and subsidiary components of predation were demonstrated in a predator-prey situation involving the predation of sawfly cocoons by small mammals. One of the basic components, termed the functional response, was a response of the consumption of prey by individual predators to changes of prey density, and it appeared to be at least theoretically important in population regulation: Because of this importance the functional response has been further examined in an attempt to explain its characteristics.
Two test diets with different acid detergent fiber (ADF) concentrations (15% ADF, 30% ADF) were fed to seven adult hindgut-and seven adult foregut-fermenting primates. Apparent digestibilities (%) of dietary dry matter (DM), gross energy (GE), and fiber components (neutral detergent fiber [NDF], ADF, hemicellulose [HC], and cellulose [C]) were measured. Rates of digesta transit (TT1) and retention (RGIT) times were assessed using acetate beads, Co-ethylenediaminetetraacetic acid, and Cr-mordanted fiber as markers. Apparent digestibilities (%) of components of the 15ADF and 30ADF diets, respectively, by hindgut versus foregut fermenters were 69.3 and 61.7 versus 81.2 and 76.7 for DM, 68.5 and 61.5 versus 80.9 and 75.6 for GE, and 44.8 and 47.4 versus 77.1 and 74.7 for NDF. No significant differences in TT1 or RGIT between dietary treatments or markers were detected. The role of plant fiber in maintaining the health and normal function of the gastrointestinal tract in captive leaf-eating primates is discussed. Zoo Biol 18:537–549, 1999. © 1999 Wiley-Liss, Inc.
Data are presented here on the feeding ecology of wild mountain gorillas (Gorilla gorilla beringei) which were observed for approximately 2,400 hours over a 17-month period in the Parc National des Volcans, Rwanda. Aspects of the relationship between the composition, diversity, and temporal consistency of the gorillas' diet and spatial and temporal variability in food distribution patterns are described. Mountain gorillas are folivores that show considerable specialization on plant parts, species and families. This pattern is facilitated by the general richness of their habitat. Their environment is heterogeneous, and spatial variability in food distribution is more pronounced than temporal variability. The gorillas rely almost completely on perennially available foliage of herbs and vines. Their diet varies little in association with seasonal factors but varies markedly in space in association with variability in the vegetational composition of the habitat. Individuals in the main study group shared basically similar patterns of food choice. Different groups also shared a similar general pattern, although there were differences in detail that apparently resulted largely from vegetational contrasts between home ranges. The gorillas' behavioral responses to environmental complexity lend general support to recent ideas concerning the evolution of their social system.
Descriptions of social organization based on interactions are difficult for fission-fusion primates, such as pygmy chimpanzees, as interactions may depend on association in parties. Frequencies of male-male and male-female affiliative and female-male and female-female aggressive interactions among Lomako pygmy chimpanzees occurred in proportion to the presence of each sex in parties. Male-male aggression and female-male affiliation, however, were more frequent than expected on the basis of party membership. Females with small swellings received more grooming and less mating than expected. Patterns of interactions at Lomako also varied with party size. Female-female affiliation predominated in small parties, while male-female affiliation predominated in larger parties. This trend parallels observed differences between the Lomako and Wamba study sites. Male-female affiliation is more frequent at Wamba where party sizes are larger. Differences between study sites may also reflect provisioning, habituation, predator threat, and habitat. Provisioning at Wamba may result in higher frequencies of aggression among males and lower levels of aggression among females. Comparison between earlier and later Lomako studies suggests that increased habituation is associated with greater differences from, rather than more similarity to, results from Wamba. Differences between Lomako and Wamba in habitat, provisioning, and human (but not non-human) predation, by affecting party size and composition, most likely account for the observed differences in social organization between the two sites.
Aim Studies comparing feeding habits across a genus in different geographical regions or habitats can identify factors associated with adaptive feeding behaviour, linking key ecological traits between consumers and their environment. We investigated biogeographical patterns in dietary composition and trophic diversity across the genus Martes in relation to geographical range and environmental variables. We hypothesized that widely distributed opportunistic Martes species should demonstrate adaptive variations in dietary composition and trophic diversity relative to regional geographical location (e.g. latitude, elevation), environmental variation (e.g. temperature, rainfall, snow cover and primary productivity) and concomitant variation in food supply.
The assumption that nonseasonal, evergreen, rain forests contain more continuously available food resources than seasonal rain forests is fundamental to comparisons made between the socioecology of the male-bonded Pan troglodytes and the female-based social system of the Pan paniscus. Chimpanzee females may be less social due to the high costs of feeding competition, whereas in the more food-rich central African rain forests such as the Lomako forest, female bonobos can associate and socially bond. The Lomako Forest experiences two wet and two dry seasons a year. Data on fruit abundance and sociality show that despite monthly variation in fruit availability, there was no consistent seasonal variation in fruit abundance or dietary breadth. Bonobo use of nonfig fruits, figs, THV, and leaves did not follow seasonal patterns. Leaves and THV may act as complementary sources of plant protein and their use was inversely correlated. Monthly variation in fruit abundance was associated with a significant decrease in the number of males in a party but not in the number of females. Focal males were frequently solitary during 1 of the 3 months with the smallest party sizes. In contrast, females remained social with each other throughout the year. Therefore, seaonality at Lomako appeared to be less marked than at comparable chimpanzee sites, such that the variation in fruit abundance did not fall below a level that prohibits female sociality.