Humans show remarkable differences in social behaviour between families, groups, communities and cultures, whereas such group-level within-species variation in socio-behavioural propensities is typically overlooked in other species. Studies on intraspecific variation in animal social structures are needed to inform an evolutionary account of human sociality. Here, we study multiple independent bonobo populations (n = 6) in zoological settings to investigate if and how bonobos (n = 70) show group-specific signatures in sociality. By applying tailored Bayesian statistical methods, we find that beyond individual and dyadic variation, the groups substantially differ from each other in core dimensions of great ape sociality: social proximity, grooming and play. Moreover, the groups’ network structures are distinct regarding cohesiveness and clustering, with some groups forming cohesive wholes, while others showcasing high levels of sub-grouping. Overall, while there is consistent evidence of differences in sociality between the groups, the patterns of cohesiveness and clustering are not consistent across the networks. This suggests that rather than groups having different levels of sociality, different patterns of sociality exist in each group. These findings warrant caution with characterising bonobos’ behavioural phenotype at the species level, and identify an essential source of variation that needs to be integrated in phylogenetic analyses.

Apes, like many frugivorous animals, are crucial allies for the reproduction of several fruiting tree species. Almost all apes, however, including bonobos Pan paniscus, are threatened with extinction. How will this affect tree conservation? How can plants that are adapted to seed dispersal by apes reproduce without their dispersal vectors? At LuiKotale, in an evergreen tropical forest of the Democratic Republic of Congo, the recruitment of 22 plant species in the absence of seed dispersal was investigated under the parental canopy, where a proportion of seeds fall without horizontal dissemination. Most bonobo-dispersed plant species (95% of 19 species) were unable to self-recruit under the canopy. As 40% of the tree species (65% of trees) at LuiKotale are dispersed by bonobos there is a risk of ecosystem decay and simplification (reduced biodiversity) if Pan paniscus disappears from its natural range. The extinction of other apes from their forests could have similar consequences. The conservation of tree species, therefore, must encompass conservation of pollinators, seed dispersal vectors and other species that provide ecological services to the trees and other fruiting plants.

Over 8 months we surveyed the Lake Tumba landscape, Democratic Republic of Congo, walking 86 km of transects and 324 km of reconnaissance, to document the distribution and estimate the abundance of great apes. Five separate groups of bonobo Pan paniscus were located in the areas of Bolombo-Losombo, Mbala-Donkese, Ngombe-Botuali, Botuali-Ilombe, and Mompulenge–Mbanzi-Malebo–Nguomi, and one population of chimpanzees Pan troglodytes in the Bosobele-Lubengo area. Mean bonobo densities ranged from 0.27 individuals km-2 in the vicinity of Lake Tumba to 2.2 individuals km-2 in the Malebo-Nguomi area. In the latter they appear to be living at a higher density than reported for any other site. This may be due to the area's forest-savannah mosaic habitat, which may provide year-round fruit sources, with bonobos falling back on savannah fruits when forest resources are scarce. The bonobos of the Bolombo-Losombo area and the Bosobele-Lubengo chimpanzees have low relative abundances and live in marginal habitats of islands of terra firma within inundated forests.