Socioecological models try to explain social organization in terms of ecological factors that influence social interaction patterns.  Most models of primate socioecology concentrate on aspects of feeding ecology, particularly the degree and nature of competition that individuals face both within and outside their groups.  More recently, the protection that males may offer females and their young against infanticidal male rivals has also featured in these models.  However, none of the published models, which are meant to apply to primates generally, accurately describes the African guenons (including blue monkeys).  These species are largely frugivorous, like other forest living monkeys (e.g. macaques), but their social relations appear to be substantially different, especially in terms of agonistic behavior.  The idea that females bond with protective males is also not well supported by the observations we have made.  

My field work includes collecting systematic records on social behavior of adult female and juvenile blue monkeys to document patterns of affiliative and agonistic behavior, as well as patterns of feeding and space use.  These data have revealed very low rates of agonistic behavior and the absence of a detectable dominance hierarchy over periods in which such a hierarchy would be easily detected in other Old World monkeys.  By combining data across several years, an hierarchical organization to dyadic dominance relationships becomes apparent, but it is definitely not a salient feature of blue monkey society.  Dominance rank correlates with few behavioral measures, and so far seems unrelated to reproductive success.  In addition, and in contrast to other more ‘dominance-oriented’ primate species, coalition formation is exceedingly rare.  We are currently working on a comprehensive description of the dominance system of blue monkeys, based on 12 years of data from multiple groups (see Keren Klass's page).  It appears that these hierarchies are generally moderately linear, and asymmetries within dyads are marked, however the hierarchy is not a very steep one.  As in other cercopithecines, there is evidence for inheritance of rank among females.Marina watching
Whether there is an ecological explanation for these weak agonistic asymmetries is still an open question, and one that I continue to work on by expanding data collection to cover all the seasons of the year.  The results so far suggest that the nature of food resources (whether fruit or leaf, clumped or dispersed) is not as important as the way individuals use those resources: in particular, when animals can spread out as blue monkeys do, overt competition is avoided, and societies can be non-hierarchical.  Karen Pazol’s thesis supports this conclusion with meticulous data on food availability.  By contrast, Steffen Foerster's thesis did show some rank effects related to food competition and diet, and ultimately to fecal glucocorticoids in one of two groups.  These are the first substantial rank-related fitness correlates we've found, but it remains to be seen if they do ultimately influence reproductive success. Groups may differ because of the way in which their members "handle" competition, i.e. whether they spread out or not, and also according to the main dietary items they consoume.  

My new project aims to understand how group size may affect the social lives andreproduction of females and males. Recent group-fissions give us an unprecedented opportunity: however, so far, quite a few of the patterns we've seen don't seem (again) to fit what the models tell us should happen. Here is the public abstract from the NSF website about this project:

Sociality is a hallmark of the primate order, and understanding the selective advantage of group living has proved an enduring question. The researchers are studying six groups of wild blue monkeys (Cercopithecus mitas stuhlmanni), differing five-fold in size, in the Kakamega, Kenya rain forest to understand the evolutionary basis of group living. This project focuses on how variation in group size influences biological fitness of wild female and male blue monkeys. Group size is expected to reflect costs and benefits of group living to individual group members. Females compete aggressively with group-mates over access to food, and engineer group splits when groups become large. Such observations suggest costs to living in larger groups, while collective territorial and predator defense, mainly by females, also suggest benefits. The research team investigates how group size influences female fitness, measured directly in terms of inter-birth interval, infant survival, and age at first birth, and indirectly by aspects of feeding and social behavior. Males of this species try to monopolize groups of females, and should have more reproductive opportunities in larger groups. Models of male reproductive partitioning suggest additional important factors, however, like female reproductive synchrony, intruder pressure and a male's own reproductive history. This project clarifies which factors best explain the considerable variation in reproduction among males. The researchers monitor demographic changes, female social and sexual behavior, and collect fecal samples for genetic paternity assignment using microsatellite loci. The study population is one of very few in which long-term demographic data exist. This project directly measures reproductive outcomes as related to social and ecological drivers.

Our descriptions of blue monkey societies are also related to a very different and active area of research, namely the evolution of intelligence in the primate order.  An influential hypothesis explaining the evolution of primate intelligence relates it to solving the problems of life in a social network.  As the name of the "Machiavellian intelligence hypothesis" suggests, primates might have evolved their characteristic intelligence to steer through a maze of social bonds that are used to influence competitive outcomes through asymmetries in power.  This hypothesis, however, is based largely on the behavior of a few relatively well-known species whose societies are characterized by salient  competition and dominance relations.  In these species, the formation of coalitions seems to improve individuals’ strategic position in competitive situations.  In species like blue monkeys, in which competition and dominance are not salient features of social life, the effectiveness of using social connections to improve competitive power may be limited.  However, hypotheses that explain the evolution of primate-wide cognitive abilities must clearly apply to the entire order, not just a limited set of species.  The existence of relatively non-competitive social systems, like those of blue monkeys and other primate species, thus seems problematical for this hypothesis.