Nest Grouping Patterns of Bonobos (Pan paniscus) in Relation to Fruit Availability in a Forest-Savannah Mosaic

Abstract

A topic of major interest in socio-ecology is the comparison of chimpanzees and bonobos' grouping patterns. Numerous studies have highlighted the impact of social and environmental factors on the different evolution in group cohesion seen in these sister species. We are still lacking, however, key information about bonobo social traits across their habitat range, in order to make accurate inter-species comparisons. In this study we investigated bonobo social cohesiveness at nesting sites depending on fruit availability in the forest-savannah mosaic of western Democratic Republic of Congo (DRC), a bonobo habitat which has received little attention from researchers and is characterized by high food resource variation within years. We collected data on two bonobo communities. Nest counts at nesting sites were used as a proxy for night grouping patterns and were analysed with regard to fruit availability. We also modelled bonobo population density at the site in order to investigate yearly variation. We found that one community density varied across the three years of surveys, suggesting that this bonobo community has significant variability in use of its home range. This finding highlights the importance of forest connectivity, a likely prerequisite for the ability of bonobos to adapt their ranging patterns to fruit availability changes. We found no influence of overall fruit availability on bonobo cohesiveness. Only fruit availability at the nesting sites showed a positive influence, indicating that bonobos favour food ‘hot spots’ as sleeping sites. Our findings have confirmed the results obtained from previous studies carried out in the dense tropical forests of DRC. Nevertheless, in order to clarify the impact of environmental variability on bonobo social cohesiveness, we will need to make direct observations of the apes in the forest-savannah mosaic as well as make comparisons across the entirety of the bonobos' range using systematic methodology.

A Comparison Between Bonobos and Chimpanzees: A Review and Update

“…The chimpanzee geographical range is considerably larger and more diverse than that of bonobos, extending from deep equatorial rainforests to savannah‐like environments spanning 21 countries . In contrast, bonobos are endemic to the forest‐dominated Congo river basin, although this range also encompasses savannah mosaic ecosystems . Although still under investigation, the bonobo ecological range appears to be part of the chimpanzee range .…”

Forest cover, hunting pressure, and fruit availability influence seed dispersal in a forest‐savanna mosaic in the Congo Basin

“…Nevertheless, S. kamerunensis is among the most common tree species in the area (Bastin ), and it fruits during the dry season, a period of relatively low fleshy fruit availability (Serckx et al . ). We therefore believe that S. kamerunensis fruits account for a relatively large share of community‐wide fruit availability, and hence the satiation level of dispersers, during this period.…”

“…This species fruits during the dry season, a period of relatively low overall fruit availability (Serckx et al . ), and is among the most common trees in the study area (6.63 stem/ha, Bastin ). We therefore considered S. kamerunensis a good predictor of overall fruit availability during the study period.…”

“…The index is therefore a function of both S. kamerunensis fruiting tree density and trunk size (diameter at breast height, dbh), which is considered the most accurate way to estimate the fruit abundance of tropical trees (Chapman et al 1992). This species fruits during the dry season, a period of relatively low overall fruit availability (Serckx et al 2014), and is among the most common trees in the study area (6.63 stem/ha, Bastin 2014). We therefore considered S. kamerunensis a good predictor of overall fruit availability during the study period.…”

First quantitative survey delineates the distribution of chimpanzees in the Eastern Central African Republic

“…For the nest production rate we used i) r = 1.14 as reported for three habituated wild chimpanzee communities in Tai National Park, Republic of Côte d'Ivoire (Kouakou et al, 2009) and ii) and r = 1.09, a value often cited in the literature and reported from both the Budongo forest (Plumptre and Reynolds, 1997a) and the lowland tropical forest in northern Congo (Morgan et al, 2006). For the mean nest lifetime t we evaluated 22 studies from 16 different locations across the whole species range of chimpanzees (Blom et al, 2001;Carvalho et al, 2013;Devos et al, 2008;Fleury-Brugiere et al, 2010;Ghiglieri, 1979;Hall et al, 1998;Hicks et al, 2014;Ihobe, 2005;Kouakou et al, 2009;Marchesi et al, 1995;Matthews and Matthews, 2004;Moyer et al, 2006;Ogawa et al, 2006;Reynolds, 1997a, 1996;Pruetz et al, 2002;Serckx et al, 2014;Stewart et al, 2011;Tutin and Fernandez, 1984;Van Krunkelsven, 2001). We then considered the median estimate per location to obtain four different estimates used in this study: the median estimate of all ecotone locations matching our habitat (Lopé NP Gabon, Niokolo Koba NP Senegal, forest-savanna mosaic of western DRC, Ugalla Forest in Tanzania, Haut Niger NP in Guinea and Lagoas de Cufada Natural Park in Gambia, 140 days), the median estimate of all 16 locations (120 days), as well as 1.5 × more and less than this global median (180 and 80 days, respectively).…”