Vervet monkeys socialize more when time budget constraints are experimentally reduced

Abstract

In species that live in stable groups, successful management of time budget (i.e., the proportion of time involved in different behaviours) and social relationships has been proposed to be a key variable affecting individual fitness. Such management is limited by time constraints, which are group size and season dependancy. However, the link between time budget constraints and grooming patterns as a means to service social relationships has never been studied experimentally. Here, we reduced the time constraints of three wild vervet monkey (Chlorocebus aethiops pygerythrus) groups by offering them high quality food for 60 min in the morning. We conducted 10 trials in summer and 10 trials in winter. We found that vervet monkeys indeed reduced the proportion of time spent foraging during the rest of those days compared to control days and increased the proportion of grooming time spread over more bouts. Individuals that did not get access to the food still participated as much in grooming as those that did eat. In accordance with our expectations, social network analysis revealed a larger grooming network on supplementation days: vervet monkeys used their extra time to socialize with more different group members. Furthermore, following our predictions, the effect of provisioning was usually stronger during the winter season (when food was scarce and days shorter) than during the summer, and the number of conflicts decreased during supplementation days. Finally, despite the fact that adults and juveniles of all three groups increased their proportion of time spent grooming during supplementation days, few group and age differences emerged in the way vervet monkeys manage their time budget. Interestingly, some of these differences seem to be independent of group size. In conclusion, vervet monkeys seize the opportunity to increase the proportion of time spent in social behaviours if time budget constraints are reduced.

From temporal network data to the dynamics of social relationships

“…Here, we have presented a new framework to go from a stream of interactions to a quantification of the strength of ties in a social network and to study their dynamic evolution, based on the idea that social relationships are interdependent: since time resources to invest in social relationships are limited [45], reinforcing a relationship with someone is necessarily done at the expense of the relationships with others. While this idea can be translated in various ways into specific rules of evolution, here we have focused on a parsimonious two-parameter model rather than on more complex alternatives.…”

“…The evolving weight w ij (t) of the tie between nodes i and j represents a quantification of the strength of their relationship at t. Moreover, our framework goes beyond the few such dynamic network models proposed to date [35][36][37][38], that are based on the idea that the weight of a tie between two individuals strengthens when they interact, and that in the absence of interaction, the tie's weight decays exponentially with time (the time scale of the decay is the model's parameter): these rules of evolution assume that the links between distinct pairs of individuals are independent, while the interdependence of social relationships is instead often well justified. For instance, in the complex social groups formed by humans and other primates [39][40][41], investing in a social relationship is a costly strategic decision that requires specific cognitive skills [42] and the quality of an individual's social relationships depends on the time invested in them [43][44][45]. Thus, the occurrence of a social interaction between two individuals not only reinforces their mutual relationship, but it also weakens the relationships they have with others: the time and energy spent to maintain the tie with an individual is taken from a finite interaction capacity and thus is time that is not spent with others.…”

Laughter and its role in the evolution of human social bonding

“…(Note that all other activities, including territory defence, evicting intruders, territorial advertising, scent marking, defecating etc, take up a negligible amount of time, and can be ignored for these purposes.) That primates, in particular, face serious time constraints is attested to by observational data on maternal time budgets (mothers are obliged to increase feeding time and reduce social time as the infant's lactational demand increases with age [ 48 , 49 ]) and by field experiments that have manipulated food availability (with the reduction in feeding time as a result of artificial feeding being converted into social grooming) [ 50 ].…”

Regulation of inter-sexual relationships within the microcosm of Guinea baboon units

“…While males maintained a constant number of grooming interactions, irrespective of their unit size, the frequency they were in proximity to females and their greeting rates varied with unit size. Maintaining equal grooming relationships with an increasing number of associated females might be too time intensive for males to realise without reallocating time from other important activities (Borgeaud et al, 2021;Dunbar et al, 2009). Greeting interactions, in contrast, are not time intensive and, therefore, less costly to increase in frequency.…”