On the neglected behavioural variation among neighbouring primate groups

Abstract

Behavioural variation in primates has been well studied at the level of individuals by behavioural ecologists, and more recently at a population level by cultural biologists. Behavioural differences between groups of the same population, however, have rarely been considered. Here, I review intergroup variation in universally occurring behaviours between up to six neighbouring groups of vervet monkeys. Group differences have been found in several domains including foraging, conflicts, grooming and proximity. An exclusively ecological explanation for the observed variation appears implausible, as these monkey groups have overlapping home ranges, and their ecology is therefore very similar. The presence of a genetic bias underlying the observed group differences is also implausible, as males disperse between groups at sexual maturity and multiple times within their lives creating a continuous gene flow between the six groups. This leaves socially learned group‐level traditions as the most plausible explanation. I discuss ways in which this working conclusion can be tested. The likely presence of group‐level traditions in close proximity, well known in humans, has rarely been considered for non‐human primates and adds an important dimension to research on conformity in non‐human cultures.

Wild primates copy higher-ranked individuals in a social transmission experiment

“…Overall, these analyses provide evidence that social transmission was option specific, i.e., observing lift increased the rate at which observers learned to solve the task using the lift option, and likewise for the pull option (see Table 2 for estimates of effect sizes and total support for each network). This suggests, confirming previous studies 25,26,44,45 that vervet monkeys demonstrate social transmission that could lead to foraging group-level traditions. However, we also found that once an individual had solved the task using one option it became an estimated 31x more likely to asocially learn the other technique than individuals naive to both techniques (95% CI = 11.3-110.6, support = 100.0%, Table 2, see section "Testing whether the learning generalization effect operated on asocial or social learning" In Supplementary Note 2).…”

Behavioural diversity of bonobo prey preference as a potential cultural trait

“…However, to distinguish whether social processes contribute to the emergence of behavioural phenotypes, it is essential to quantify ecological variation and account for its influence on behaviour expression, a challenging endeavour in wild settings. Few studies have attempted to limit potential ecological confounders by investigating behavioural diversity between neighbouring groups ( Luncz and Boesch, 2014 ; Pascual-Garrido, 2019 ; van de Waal, 2018 ). Nonetheless, in the absence of between-group range overlap, fine-scale ecological variation specific to the locations where behavioural phenotypes are expressed cannot be excluded.…”

Living in the suburbs: Space use by vervet monkeys (Chlorocebus pygerythrus) in an eco‐estate, South Africa

“…The same may be true for troops within the same population that occupy habitats with differential availability, distribution and quality of resources (e.g. Bronikowski & Altmann, , van de Waal, ). Thus, regardless of the intensity or duration of research, studies with small sample sizes are unable to assess the effects of local habitat differences, or take into account individual differences among troops (Isbell & Young, ).…”

“…Studies with large sample sizes of troops (e.g. Bronikowski & Altmann, ; van de Waal, ) or complete populations (e.g. Hamilton, Buskirk & Buskirk, ; Iwamoto, ; Takasaki, ) are rare.…”

“…Hamilton, Buskirk & Buskirk, ; Iwamoto, ; Takasaki, ) are rare. However, within species, disjointed populations living under different ecological conditions may differ more from one another in their ranging patterns than they do from closely related species (Dunbar, ; Strier, ; van de Waal, ). The same may be true for troops within the same population that occupy habitats with differential availability, distribution and quality of resources (e.g.…”