Bonobo social organization at the seasonal forest-savanna ecotone of the Lomami national park.

Abstract

Examining the relationship between food and primate social organization helps us understand how the environment shaped hominin social evolution. However, there is debate as to whether the social differences between our two closest relatives, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes), are due to differences in food availability between their respective habitats or to nonenvironmental factors. The most prominent theory is that bonobo communities have more socially cohesive, stable parties, centered on gregarious females because they evolved in food-rich habitat where individuals, especially females, are less burdened by competition with groupmates. However, more research on bonobos in habitats with seasonal variation in food is needed. This study measured food availability and bonobo social organization at Luzaka, a new site in a seasonal forest fragment. Fruit abundance and dispersion were recorded for a year at Luzaka with the same methods used at Wamba, a bonobo site in more seasonally stable habitat and terrestrial herbaceous vegetationdensity was measured. At Luzaka, bonobo parties were also recorded for a year using camera traps. Fruit was more seasonal and dispersed at Luzaka than at Wamba. However, the social organization of Luzaka bonobos resembled social organization of bonobos at less seasonal sites. There were minor effects of fruit clumping on party size without effects on the proportion of females in parties suggesting that at Luzaka, the clumping of fruit slightly affected social cohesiveness but does not disproportionately affect females. Bonobo social cohesiveness and female gregariousness appears consistent and compatible with seasonal habitat.