Variations in competitive mechanisms of captive male hamadryas-like baboons in two feeding situations

Experiments were carried out to determine the influence of food distribution (clumped vs dispersed) on processes of competition among seven captive male hamadryas-like baboons. Spatial cohesion, cohesive behaviours that males performed and received from their females, and aggressive and feeding behaviours of the males were collected during 35 min after food supply. Median values and variability of these variables were compared in both the feeding situations. Food distribution influenced both asymmetries in access and the form of competition. When food was clumped, those with less access fed by means of compensatory or alternative strategies (away from the main source and/or by feeding supplants), and they were more aggressive towards other males. When food was dispersed, all individuals could feed simultaneously, males that were more aggressive were those with less cohesive OMUs, despite the fact that cohesive behaviours remained constant. Females appeared to contribute to variation in the OMU's cohesion through their responses to both food distribution and males' competitive ability.     

Ecological determinants of the behavior and social structure of Japanese monkeys: A synthesis

A review is presented of the results of the various studies in this volume and an attempt is made to establish connections among several features of the ecology, behavior, and social structure of Japanese monkeys. Several studies in this volume suggest that intergroup direct feeding competition has been much more severe in Yakushima, in the warm-temperate region, than in Kinkazan, in the cool-temperate region of Japan. This result is consistent with the predictions that moderate abundance and clumped distribution of food incur more severe intergroup direct competition. However, the number of adult females within a group in Yakushima was smaller than that in Kinkazan even though severe intergroup direct competition should favor large groups. This contradiction can be mainly explained by the less severe intergroup indirect competition in Kinkazan than in Yakushima. By contrast, some studies in this volume also indicate that adult male to female ratio within a group has been higher in Yakushima than in Kinkazan. This result can be explained in two ways: the females in Yakushima might have recruited more males to increase the competitive ability of the group under conditions of severe intergroup direct feeding competition; alternatively, it might be profitable that the males in Yakushima defend females cooperatively as group males against the males in other groups at a moderate density of females. Some studies in this volume suggest that grooming frequency was higher in Yakushima than in Kinkazan. The higher grooming frequency in Yakushima might have been partly due to a constant increase in engaging in social behavior from a decrease in feeding time. Another reason might be that there is a stronger effect of grooming on promotion of formation of coalitions among adults under conditions of severe intergroup direct and intragroup direct competition.     

Females drive primate social evolution

Within and across species of primates, the number of males in primate groups is correlated with the number of females. This correlation may arise owing to ecological forces operating on females, with subsequent competition among males for access to groups of females. The temporal relationship between changes in male and female group membership remains unexplored in primates and other mammalian groups. We used a phylogenetic comparative method for detecting evolutionary lag to test whether evolutionary change in the number of males lags behind change in the number of females. We found that change in male membership in primate groups is positively correlated with divergence time in pairwise comparisons. This result is consistent with male numbers adjusting to female group size and highlights the importance of focusing on females when studying primate social evolution.     

One-male units and clans in a colony of hamadryas baboons (Papio hamadryas hamadryas): effect of male number and clan cohesion on feeding success

In the multilevel societies of hamadryas baboons, adult males can be attached to single one-male units (OMUs) or to clans containing several such OMUs. This paper examines the effect of male number and rivalry between males within a clan on their ability to compete for access to a clumped food resource. The data come from a study of a multilevel colony of hamadryas baboons (Papio hamadryas hamadryas) housed at the Madrid Zoo. The colony consisted of 12 harem-holding males and 40 sexually mature females, and was organized into five single OMUs and two clans (containing three and four OMUs, respectively). The top-ranking male of one of the clans was removed and later reintroduced, so the study involved an analysis of the composition of clans and OMUs and of the males' use of the feeding area across three study periods: preseparation, separation, and reintroduction. The findings reported indicate that both males and females derived clear advantages in the context of contest competition for access to clumped food if they were members of clans, because the males and females from large clans had a feeding advantage over those from smaller clans and single OMUs. Furthermore, rivalry among males within the clan reduced their ability to compete for food against males outside their clan. This paper provides empirical evidence for one of the potential advantages that hamadryas males may enjoy if they are attached to clans, and also provides empirical support for the general hypothesis that a large number of males in a group may provide fitness-related benefits to the group members, provided they are able to cooperate with each other.     

Sex-specific aggression and sex ratio in wintering finch flocks: serins and siskins differ

Males are dominant over females in many bird species. This may lead to male monopolisation of resources whenever food is scarce or clumped and secondarily to lower female survival rates. As a result of the consequent male-biased sex ratio in the adult population, competition may arise either (1) between males and females, as males attempt to exclude females from feeding patches, or (2) between males because females do not pose a competitive threat. We recorded agonistic interactions between males and females in wintering foraging flocks of serins (Serinus serinus) and siskins (Carduelis spinus) to test for inter-specific differences. Most of the aggressive interactions in serins were between males and females, whereas in siskins they were between males. We also compared sex ratios for each species during the winter, determined from separate trapping efforts over an 11-year period, to test whether the direction of aggression by males (i.e. male/male; male/female) relates to variations in female survival rates. The proportion of females was smaller in winter than in autumn for serins, but differences in siskins were negligible. Results are interpreted in relation to the social organization displayed by both species studied.     

Influence of food dispersion on feeding activity and social interactions in captive Lophocebus albigena and Cercocebus torquatus torquatus

We analysed the impact of the distribution of food items on feeding activity and social interactions in captive red-capped and grey-cheeked mangabeys. Three different feeding situations were presented: food items were either placed in a single heap or dispersed in several smaller heaps on the ground or in space. Social interactions were estimated by the frequency of positive, as well as of negative social interactions and by the structure of visual social attention. Feeding activity was estimated by proximity to food and feeding frequency. When food items were presented in single heaps, the adult males monopolized the food and monitoring of conspecifics increased. Social interactions and social gazes decreased in numbers when food items were dispersed in 3D. Gazes were directed more frequently towards the adult males when food items were presented in a single heap. Juveniles and some nonreproductive adult monkeys were the most affected by food competition situations. Inter-group variations, within a given species, of the behavioural responses observed in relation to the distribution of food items were evidenced. This suggests that social context, i.e., individual histories and relationship between group members, plays an important part in the expression of the activities of each member in a group.     

Mating Tactics in Male Grey-Cheeked Mangabeys (Lophocebus albigena)

Reproductive tactics of males can change with individual quality, relatedness and social structure. Here we describe the behaviours of male grey-cheeked mangabeys towards other males, and females and their offspring ( Lophocebus albigena ) in relation to male status (high-ranking/low-ranking/transient) and group composition in Kibale National Park, Uganda. High-ranking males had the highest mating success, frequency of loud calls, mate guarding and aggression towards females and males. Only transient males were often observed to be aggressive towards juveniles, while some high-ranking males provided infant care. Mating tactics of high-ranking males varied greatly among the five studied groups, probably as a function of the intensity of male–male competition. These results are discussed with regard to the role of male–male competition and behaviours that could affect female mate choice as tactics to obtain reproductive success.     

Evolution of Pair-Living in <Emphasis Type="Italic">Phaner furcifer</Emphasis>

Pair-living evolved several times independently in the primate lineage and most likely for more than one reason. Currently, there are 7 hypotheses regarding the evolution of pair-living in primates. They may explain several but not all cases. I investigated the applicability of the explanations to fork-marked lemurs Phaner furcifer. I used information from a long-term study on 8 fork-marked lemur families in Kirindy Forest to evaluate the hypotheses. Fork-marked lemurs live in uniform dispersed pairs, which share and defend a territory but spend three-quarters of their activity time apart from each other. Unconditional female dominance and lack of permanent close association between pair-partners disqualify most hypotheses. Lack of male parental care and long travel distances in small home ranges disqualify other explanations. I conclude that there is no support a priori for any current pair-living hypothesis and that the newly formulated intersexual-feeding-competition hypothesis best explains the evolution of pair-living in fork-marked lemurs. Accordingly, female range exclusivity evolved first as a consequence of intense feeding competition. Subsequently, indirect feeding competition drove females to accept a single male to share their territory as a defense against feeding competition from males whose ranges unsystematically overlap those of several females. This situation led to pair-living because formation of dispersed one-male-multifemale-units was too costly for males in terms of reduced foraging efficiency.     

Number of males in primate groups: Comparative tests of competing hypotheses

Primate social groups frequently contain multiple males. Male group size has been hypothesized to result from male mating competition, but the selective factors responsible for the evolution of multimale groups are unclear. Short breeding seasons create situations that are not conducive for single males to monopolize mating access to females, and may therefore favor the formation of large male groups. Alternatively, since the costs of mate defense increase with the spatial clumping of females, female group size may be a primary determinant of the number of males in a primate group. We used comparative methods designed to control for the potentially confounding effects of hidden third variables associated with phylogeny to test the breeding season and female group size hypotheses for the evolution of multimale groups. Our results revealed no association between breeding season duration and the number of males in groups. In contrast, we provide support for the female group size hypothesis by demonstrating a strong pattern of correlated evolution between female and male group size. © 1996 Wiley-Liss, Inc.     

Female dominance and feeding priority in a prosimian primate: experimental manipulation of feeding competition

Female dominance and feeding priority are considered unique behavioral strategies in many Malagasy lemuriformes, particularly Lemur catta. Two hypotheses have been introduced to explain these behavior patterns: 1) females are agonistically dominant over males to mitigate female-male food competition so that females can compensate for high energy demands and inefficient reproductive physiology, and 2) males defer to females when feeding as a reproductive strategy. We tested these hypotheses by conducting controlled feeding experiments on free-ranging ring-tailed lemurs (Lemur catta) on St. Catherine's Island, GA. Food was dispersed in three ways to simulate varying patch sizes. All feeding and agonistic interactions were recorded during each trial (n = 24). The degree of relatedness between individuals was determined using DNA fingerprinting. There was a clear relationship between food dispersion and both expression of female dominance and feeding priority. Elements of both hypotheses were supported because male and female L. catta used different strategies depending on rank and the dispersion of food. Interpretation of the impact of male rank was complicated because the younger, low-ranking males had female relatives in the group. Females fed more than males, and rates of aggression decreased as food dispersion increased. High-ranking, older unrelated males deferred to females and received little aggression. The top-ranking male deferred the most and sired most if not all of the offspring. Low-ranking, younger related males fought with females for access to food sources, received more aggression, and did not sire offspring.     

Time and energy constraints and the evolution of sexual size dimorphism — to eat or to mate?

Summary We present an empirical test of the Ghiselin—Reiss small-male hypothesis for the evolution of sexual size dimorphism (SSD). In mating systems dominated by scramble competition, where male reproductive success is a function of encounter rate with females, small males may be favoured when food is limiting because they require lower absolute amounts of food. Given a trade-off between time and energy devoted to foraging and to mate acquisition, small males should be able to devote more time to the latter. If at the same time larger females are favoured, this mechanism will contribute to the evolution of SSD and may be the major determinant of the female-biased SSDs that characterize most animal taxa. We tested this hypothesis using the water strider,Aquarius remigis (Heteroptera: Gerridae), a scramble competitor which mates many times over a prolonged mating season and which shows female-biased SSD. Laboratory experiments demonstrated that foraging success and giving up times (GUTs) are lower for males than for females during the reproductive season and that male water striders flexibly alter their time budgets under conditions of energy limitation. Controlled feeding experiments showed that male and female longevity, female fecundity and male mating success are positively related to food availability. As predicted, male body size is negatively correlated with several indices of male fitness (longevity, number of mating attempts and mating success), while female body size is positively correlated with longevity. These results are consistent with the hypothesis that scramble competition for mates favours small males in this species and provides empirical support for the Ghiselin—Reiss small-male hypothesis.     

Male Competition,Mating Success and Female Choice in a Seasonally Breeding Primate (Erythrocebus patas)

Mammals with restricted breeding seasons often show brief but intense bouts of male competition for mates and male reproductive success has been attributed to male competitive abilities, with the most aggressively successful males able to control access to fertile females, or with females choosing to mate with such males. We studied male competition, mating behaviour and female mate selection in patas monkeys, a primate with a restricted breeding period. We observed two habituated patas groups in Laikipia District, Kenya, during Jun.-Aug. 1983. During the study, one group had a single resident male while the other group had multiple adult males. Within the multimale group, experienced adult males were no more successful than the subadult male. The sole resident male had a significantly higher rate of fights won (p < 0.02) although he did not differ from the multimale group males in rate of aggression or initiation of fights. We found no significant differences in either mating success or female preference based on males' experience or residency. The rates at which males copulated with and were solicited by females were not significantly correlated. We found no evidence of stable dominance ranks among males in the multimale group and aggressive success was not significantly correlated with copulation rate for males in the multimale group. Subadult males were responsible for the majority of copulations observed during the final third of the breeding season. Our observations of this patas population showed a fluid number of males in groups, with the same groups able to shift rapidly from single to multimale structure. This fluidity may result from the large fluctuations in numbers of breeding-age males and females observed over 4 yr of studying this population.     

Female relationships in bonobos(Pan paniscus)

The popular belief that women are not naturally able to bond with each other is often supported by theoretical and empirical evidence that unrelated females do not bond in nonhuman primate species. Bonobos (rare and endangered African apes, also known as pygmy chimpanzees) are (with their congener, chimpanzees) the closest living relatives of humans and appear to be an exception to this characterization. Data collected on individuals representing half of the world’s captive population reveal that bonobo females are remarkably skillful in establishing and maintaining strong affiliative bonds with each other despite being unrelated. Moreover, they control access to highly desirable food, share it with each other more often than with males, engage in same-sex sexual interactions in order to reduce tension, and form alliances in which they cooperatively attack males and inflict injuries. Their power does not stem from a size equality with or advantage over males (in fact, females average 82.5% of male size), but rather from cooperation and coalition formation. The immediate advantage to female alliances is increased control over food, the main resource on which their reproductive success depends, as well as a reduction in other costs typically associated with a female-biased dispersal system, such as male agonism in the contexts of feeding competition and sexual coercion. The ultimate advantage of friendly relationships among females is an earlier age at first reproduction, which results in a large increase in lifetime reproductive success. Analysis of this bonding phenomenon sheds light on when, where, and how we should expect unrelated human females to bond with one another by demonstrating that bonding is not dependent on access to one’s relatives but rather on an environmental situation in which female aggregation is possible, coupled with an incentive for cooperation.     

Diet and dominance among female vervet monkeys (Cercopithecus aethiops)

Behavioral observations of free-ranging female vervet monkeys (Cercopithecus aethiops) suggest that priority of access to food enhances individual fitness. Seventeen adult females living in two social groups were observed for 26 months in the Samburu/Isiolo Game Reserves, northern Kenya. Priority of access to feeding and sitting sites was associated with significant differences in diet and reproduction. Food species distribution altered rank-related differences in diet. Rank-related differences in diet occurred when food items were clumped in distribution, but not when they were randomly distributed. The relation of individual food items to reproduction influenced rank-related differences in reproduction. Rank was significantly correlated with birth rate when a preferred food species was clumped in distribution.     

Female feeding priority in bonobos, Pan paniscus, and the question of female dominance

The question of whether bonobos show feeding priority and female dominance has been proposed and examined, both in the wild and in captive studies, with differing results. The relationship between female dominance and female feeding priority has been best studied in prosimian primates. These studies use established criteria of females consistently evoking submissive behavior from males in dyadic encounters for determining female dominance. Although the relationship is complex, female dominance in prosimians is associated with preferential access to food. Data from studies of wild habituated bonobos in the Lomako Forest, Democratic Republic of the Congo, are examined for evidence of both female feeding priority and female social dominance using similar criteria as used for prosimians. Bonobos showed evidence of female feeding priority in small, but not in large, food patches. Male-male competition for mating opportunities at the start of the food bout was related to some, but not all, differences in time spent feeding between the sexes. Female dominance similar to that seen in prosimians was not observed in these bonobos. Males were consistently dominant in dyadic interactions. Female feeding priority with male dyadic social dominance implies that male deference during feeding cannot be excluded as one explanation of interpretations of female dominance in bonobos. Additionally, dominance of male bonobos by females appears to require the presence of female coalition partners. As in other primates with female feeding priority, bonobo females express this trait where food is economically defendable. Unlike prosimians, however, bonobo female feeding priority may result from male deference and the importance of female coalitions in nondyadic interactions.     

Correlates of Male Consortship Rate in Free-Ranging Rhesus Macaques (Macaca mulatta)

Male–male competition for access to receptive females can take the form of nonrecurring fights and/or a sustained contest over mating opportunities. Male physical condition has been linked to dominance rank and reproductive success in species characterized by intrasexual fights for dominance and access to females. In group-living species characterized by endurance rivalry, however, factors contributing to male reproductive success are less well understood. In such species, particularly seasonally breeding ones with low sexual dimorphism and seniority-based rank, age and social factors other than rank may prove important. In the absence of genetic data, male mate guarding or consortship can serve as an indicator of male reproductive success. To evaluate the contribution of age and intragroup sociality to male consortship rate, I collected behavioral data during one nonmating and one mating season in two social groups of free-ranging rhesus macaques that experience no predation or food scarcity. Higher-ranking males, younger males, or males that exhibited lower rate of intrasexual aggression had higher consortship rates. Male–female dyads that groomed outside consortship did not form consortships as often as dyads that did not engage in nonconsort grooming. This is the first study to identify the significance of male–male aggression and male–female affiliation to male consortship rate in a species characterized by endurance rivalry, high male rank stability, and strong female mate choice. Social behaviors and male age may be particularly important in determining male reproductive success in populations experiencing high food availability and a lack of predation, which are typical of an increasing number of vertebrates in areas densely populated by humans.     

Balancing contest competition,scramble competition,and social tolerance at feeding sites in wild common marmosets (Callithrix jacchus)

Models of primate sociality focus on the costs and benefits of group living and how factors such as rank, feeding competition, alliance formation, and cooperative behavior shape within‐group social relationships. We conducted a series of controlled field experiments designed to investigate how resource distribution (one or three of four reward platforms) and amount of food on a reward platform affected foraging strategies and individual feeding success in four groups of wild common marmosets (Callithrix jacchus) living in the Caatinga of northeastern Brazil. At our field site, common marmoset groups are characterized by a single breeding female who can produce twin litters twice per year, strong social cohesion, and cooperative infant care provided principally by several adult male helpers. We found that except for the dominant breeding female, rank (based on aggression) was not a strong predictor of feeding success. Although the breeding female in each group occupied the highest rank position and obtained the greatest daily feeding success, all other group members, including adults and juveniles experienced relatively equal feeding success across most experimental conditions. This was accomplished using a balance of behavioral strategies related to contest competition, scramble competition (associated with a finder's advantage), and social tolerance (sharing the same feeding platform). Based on these results, the social structure of common marmosets is best described as “single female dominance,” with the breeding female maximizing food intake needed to offset the energetic costs associated with reproductive twinning and the ability to produce two litters per year. Cooperative infant caregiving, in which the number of helpers is positively correlated with offspring survivorship, requires a set of behavioral strategies that serve to reduce contest competition and promote prosocial behaviors at feeding sites.     

Relative fitness of alternative male reproductive tactics in a mammal varies between years

1. In many species, males can use different behavioural tactics to achieve fertilization, so-called alternative reproductive tactics (ARTs). Few field studies have measured fitness consequences of ARTs under varying environmental conditions. 2. Here, we describe fitness consequences of three phenotypically plastic ARTs in the African striped mouse (Rhabdomys pumilio) and show that relative fitness of ARTs differs between years. Each year represents a different generation. 3. For the generation living under high population density, tactics differed in relative fitness in accordance with the theory of conditional strategies, with highly successful territorial breeding males having 10 times higher success than solitary roaming males and 102 times higher success than adult natally philopatric males. 4. For the generation living under intermediate population density, the territorial breeding and roaming tactics yielded similar fitness, which would be in agreement with the theory of mixed strategies. No philopatric males occurred. 5. For the generation living under low population density, roaming was the only tactic used and some roamers had very high fitness. 6. The main prediction of status-dependent selection for conditional strategies is a correlation between fitness and status, often measured as body mass, but we did not find this correlation within tactics when more than one tactic was expressed in the population. 7. Female distribution seems to have an effect on which reproductive tactics male chose: female defence polygyny when females are clumped (interference competition), but a searching tactic when females are dispersed (scramble competition). In contrast to predictions arising from theory on scramble competition, male body mass was important in determining fitness only in the year when females were dispersed, but not in other years. 8. Our results indicate that the differentiation between conditional and mixed strategies is not an absolute one. In many other species, environmental conditions might fluctuate temporally and spatially so that the normally suboptimal tactic yields similar fitness to the (usually) dominant tactic or that only a single tactic prevails. 9. We suggest the term single strategy, independent of current fitness consequences, for systems where tactics are not genetically determined, in contrast to genetically determined alternative strategies.     

Ecology of gorillas and its relation to female transfer in mountain gorillas

Understanding the principles that underly primate social evolution depends on integrated analysis of data on behavioral ecology, demography, life history tactics, and social organization. In this paper, data on the behavioral ecology of gorillas are reviewed and comparisons made among the three subspecies. Gorillas are selective feeders; and, their patterns of food choice are consistent with models of feeding by large generalist herbivores. They rely heavily on terrestrial herbaceous vegetation, which provides an abundant supply of densely distributed food. Availability of this food varies little in space and time; and, gorilla foraging activity can maintain its productivity. The level of frugivory and the extent of seasonal variation in diet and habitat use vary among and within populations. Low variability in food distribution patterns makes cooperative defense of foraging areas not worthwhile; but, it also means that ecological costs associated with gregariousness are low. However, demographic and life history data on mountain gorillas show that these costs may be sufficient to reduce female reproductive success as group size increases. Advantages to being with high quality males apparently can outweigh these costs. The implications of these data for the evolution of the mountain gorilla social system, and the possible roles of male protection, predation, and female/female competition in this regard, are discussed.