S. Peter Henzi

Fission-Fusion Dynamics: New Research Frameworks

Renewed interest in fission‐fusion dynamics is due to the recognition that such dynamics may create unique challenges for social interaction and distinctive selective pressures acting on underlying communicative and cognitive abilities. New frameworks for integrating current knowledge on fission‐fusion dynamics emerge from a fundamental rethinking of the term “fission‐fusion” away from its current general use as a label for a particular modal type of social system (i.e., “fission‐fusion societies”). Specifically, because the degree of spatial and temporal cohesion of group members varies both within and across taxa, any social system can be described in terms of the extent to which it expresses fission‐fusion dynamics. This perspective has implications for socioecology, communication, cognitive demands, and human social evolution.

Fecal cortisol levels in free-ranging female chacma baboons: relationship to dominance, reproductive state and environmental factors.

Savannah baboons are one of the few mammalian species that do not exhibit seasonal reproduction patterns and are therefore ideally suited to study the effect of female reproductive states (cycling, pregnant, lactating) on cortisol levels independent of seasonal factors. Fecal samples from 10 free-ranging female chacma baboons (Papio hamadryas ursinus), collected during a period of 17 months, were analyzed using a steroid-extraction method. Reproductive state had a significant effect on fecal cortisol, with lowest levels found in estrous females. Fertility was not related to fecal cortisol levels; we found no significant differences between samples collected on conceptive and nonconceptive cycles. Environmental factors explained most of the variance of fecal cortisol levels. Cortisol measures were strongly correlated with seasonal differences such as daylight duration, temperature and the amount of time that baboons spent resting. We measured higher cortisol levels during winter months and suggest that this could be related to shorter resting periods and to the cold minimum ambient temperatures at this study site. Finally, we found no relationship between social rank nor the rate of agonistic interactions with basal fecal cortisol levels.

Vigilance, predator detection and the presence of supernumerary males in vervet monkey troops

To determine whether adult males provide females with a service, in this case anti-predator behaviour, in return for inclusion in a group a free-ranging troop of vervet monkeys, Cercopithecus aethiops, was observed for 9 months. Males were more vigilant than females and the discrepancy increased as the breeding season approached. Higher levels of vigilance by males were associated with their spending a greater proportion of time either isolated or exposed at the tops of trees. Males, however, were not vigilant because they were exposed but moved into such positions in order to scan the surroundings. Despite this, males were no more efficient than females at detecting predators. The top-ranking male was the most vigilant and active against predators. It is argued from these and other data that male vigilance is directed at other males and is not a quid pro quo for inclusion. Although females benefit from this vigilance they are not capable of controlling male numbers, and troops, as a consequence, contain a number of supernumerary males who may well be the beneficiaries of the vigilance of others.

Taking sociality seriously: the structure of multi-dimensional social networks as a source of information for individuals

Understanding human cognitive evolution, and that of the other primates, means taking sociality very seriously. For humans, this requires the recognition of the sociocultural and historical means by which human minds and selves are constructed, and how this gives rise to the reflexivity and ability to respond to novelty that characterize our species. For other, non-linguistic, primates we can answer some interesting questions by viewing social life as a feedback process, drawing on cybernetics and systems approaches and using social network neo-theory to test these ideas. Specifically, we show how social networks can be formalized as multi-dimensional objects, and use entropy measures to assess how networks respond to perturbation. We use simulations and natural ‘knock-outs’ in a free-ranging baboon troop to demonstrate that changes in interactions after social perturbations lead to a more certain social network, in which the outcomes of interactions are easier for members to predict. This new formalization of social networks provides a framework within which to predict network dynamics and evolution, helps us highlight how human and non-human social networks differ and has implications for theories of cognitive evolution.

MALE CONSORTSHIP BEHAVIOUR IN CHACMA BABOONS: THE ROLE OF DEMOGRAPHIC FACTORS AND FEMALE CONCEPTIVE PROBABILITIES

There is evidence for a general relationship between male dominance rank and mating success in primates, although the strength of this relationship differs among species. In chacma baboons (Papio hamadryas ursinus) male rank is found to be of more importance than in the other savannah baboon subspecies. However, even though the priority-of-access model explains the proportion of time spent in consortship for males of different rank in chacmas, highest-ranking males usually consort less often than expected. In this study, conducted in the Drakensberg Mountains of Natal and at De Hoop in the Western Cape, we investigated why dominant males in four study troops consorted only between 50% and 75% of days that they were expected to consort according to the priority-of-access model. Consortship success of highest-ranking males was primarily dependant on the number of available oestrous females in a troop. This was likely due to costs involved in consorting which limit the amount of days that a male could spend in consortship. Females pass through several cycles before conceiving and highest-ranking males were observed to consort more often on the conceptive cycle compared to the nearest nonconceptive cycle, but this was only true for males that were already resident for several months. Recently immigrated males that became highest-ranking often consorted during nonconceptive female cycles, while older, lower-ranking males consorted during the conceptive cycles. We propose that males with longer residency have more information about reproductive state of females and thus higher reproductive success than recently immigrated males.

Cohort size and the allocation of social effort by female mountain baboons

Dunbar (1992,Behav. Ecol. Sociobiol.33, 35-49) argued that constraints on social time limited the size to which savannah baboon, Papio cynocephalustroops in any given population could grow before fissioning. Since this should be reflected in population structure, we have elsewhere (Henzi et al. 1997a, Anim. Behav. 53, 525-535) constructed a model, based on a rising probability of fission, that fits the observed distribution of troop sizes of mountain baboons, P. c. ursinusin the Drakensberg mountains of South Africa and which predicts that the probability of fission will rapidly increase once a troop has more than 23 members (or 8.7 females). We test this prediction in this paper. Since Dunbar argued that females will drive fission once they cannot engage in the grooming necessary to sustain alliances, we compared the grooming interactions of adult females from four troops in the Drakensberg mountains. The mean female grooming clique size reached an asymptote at 7.4 females, so that females in cohorts of eight or more no longer attempted to groom all other females, and mean grooming bout length declined as the cohort grew to 7.9 females and then increased again. These values are coincident with the female cohort size predicted by our model of troop growth and fission. We argue that females attempt to groom all other females as well as sustain closer relationships with a few females through longer bouts of reciprocated grooming. When the demands of grooming all other females reduce bout length to a point when no reciprocated bouts are possible, female clique size is capped. As a troop continues to grow, the mechanical difficulties involved in gaining access to grooming partners leads to a reduction in the diversity of grooming relationships. This weakening of the total female network, as cliques become more differentiated, is likely to facilitate fission. We conclude that our data provide the first within-population validation of Dunbars hypothesis concerning the mechanism underpinning fission. In the Drakensberg, where there is no advantage to female coalitions, we propose, as an amendment, that females will leave a troop not to escape local competition, but to follow a male with whom they have a close friendship.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour

DO FEMALE CHACMA BABOONS COMPETE FOR A SAFE SPATIAL POSITION IN A SOUTHERN WOODLAND HABITAT

In this study troop of chacma baboons (Papio cynocephalus ursinus) at Mkuzi Game Reserve, Zululand, South-Africa, it is suggested that risk of predation and competition over safe spatial position had more importance and effect on female behaviour than did competition for food. Only 6.4% of all agonistic events were over food patches and no significant correlation was found between a females dominance rank and proportion of time spent feeding, feeding bout length or diet composition. Parameters of reproductive success, such as inter-birth intervals and infant mortality were not correlated with female dominance rank. Female mortality, however, was related to dominance rank and all of the five females who disappeared during the study were low-ranking. Four of the five females disappeared after troop fission. There is circumstantial evidence supporting the suggestion that predation by leopards is the main cause of mortality of females at Mkuzi. High levels of female aggression were recorded, with almost no occurrences of support coalitions. Most of the aggression took place among similar ranking females, or was directed by the top ranking toward the lowest ranking females. Most of the female-to-female agonistic encounters were in a social context, and more than half were over a spatial position next to other adult troop members. Aggression among females increased after troop fission. It is suggested that the higher-ranking females may be better protected from predation, through access to more central spatial positions in the troop. Indeed, a positive correlation was found between a females dominance rank and the time spent next to other adult troop members. It may be that avoiding food competition by keeping larger distances from others, while foraging, was translated in lower ranking females to a cost of higher predation risk.

Maternal investment in mountain baboons and the hypothesis of reduced care

Abstract It has been argued that female mammals should terminate expensive forms of infant care earlier as habitat quality declines. More recently it has been shown that among a variety of mammalian species, early termination of care is also associated with highly favourable conditions. In this paper we present data on maternal investment decisions among baboons (Papio cynocephalus ursinus) inhabiting the Drakensberg Mountains of South Africa, and compare these with data from East African baboon studies. Mothers in the mountain habitat face a set of environmental conditions where the problem of resource allocation to offspring is expected to be particularly acute. We begin by using the model of Altmann (1980) of maternal time budgets to demonstrate that mountain baboon mothers experience greater perturbations to their activity budgets while suckling than do mothers in other populations. They also provide consistently greater levels of care to their infants and do so in the absence of any form of overt conflict over access to the nipple. Although this investment results in a relative lengthening of the interbirth interval (IBI), it is accompanied by relatively higher infant survival. We argue that factors that influence the maternal strategy adopted by mountain baboons include slow infant growth rates and a lack of predation in the habitat which influences probability of offspring survival beyond the immediate postnatal period. We suggest that both “care-dependent” sources of mortality (e.g. female reproductive condition, the amount of milk transferred to offspring) as well as “care independent” sources of mortality (e.g. predation, infectious disease) should be considered in studies of parental investment.

Female baboons do not raise the stakes but they give as good as they get

We used data from four chacma baboon, Papio cynocephalus ursinus, troops, living in two populations, to test the raise the stakes (RTS) strategy of reciprocity. Female baboons did not raise the stakes either within or across grooming bouts. Instead they time-matched grooming contributions and divided grooming into short episodes. In addition, analysis of the grooming behaviour of frequently versus infrequently grooming dyads did not reveal differences in grooming patterns predicted by the RTS strategy. We suggest time constraints preclude the escalation of grooming bout length as required by RTS; the data were more consistent with a strategy of give as good as you get. However, this strategy could not explain all the patterns observed, and we conclude that biological market theory represents a more appropriate framework for investigating female grooming dynamics than dyadic games based on the iterated prisoners dilemma. We suggest that competitive altruism among individuals acts as a market force influencing an individuals value as a grooming partner. Copyright 2000 The Association for the Study of Animal Behaviour.

Coexistence in Female‐Bonded Primate Groups

Publisher Summary This chapter deals with the coexistence in female-bonded (FB) primate groups. The aim of the chapter is to review the data, highlighting the strengths, insights, and shortcomings of the current theoretical views of FB groups. The chapter hopes to make a case for a more nuanced framework to situate the studies of primate sociality and cognition. In mammals, social groups based on female philopatry (FB societies) are common only among New and Old World monkeys. The chapter argues that there is little evidence for either the cognitive skills or the relationships that this account requires and, on the other, that there is too little evidence to link grooming, reconciliation, and coalition formation in this way. The evidence suggests that patterns of grooming and reconciliation reflect responses to immediate problems and have short‐term benefits, while the general rarity of coalition formation, which may be due to a corresponding rarity of circumstances in which short‐term benefits could accrue to all participants, undercuts any role it might have as an organizing principle for evolutionary theories of female action. The central objective of the chapter is to understand how actors generate appropriate, contingent responses to immediate social problems. The chapter concludes that there is a good deal of empirical hay to be made by incorporating observed patterns of grooming, reconciliation, and coalition formation into a larger account of the negotiation of coexistence by female monkeys.