A landscape-wide distribution of Pan-paniscus in the Salonga National Park, Democratic Republic of Congo.

Abstract

A total of 15 discrete communities of bonobos (Pan paniscus) in the Salonga National Park (SNP) are reported: nine in the northern sector and six in the southern sector. These communities occupy about 1120[km.sup.2], representing only 3% of the total area of SNP. Average community niche width was estimated to be [approximately equal to] 80 km. Mean distances between communities were 57 km (SD [+ or -] 32) and 89 km (SD [+ or -] 70) in the northern and southern sectors respectively; thus, inter-community interactions may not occur. Adjusting densities published by Sabater-Pi and Vea (1990), Uehara (1988), (Van Krunkelsven et al. (2000, 2000a), and Kano (1992) to account for patchiness and patch width, the population of Salonga totals 1,440 bonobos at minimum: 864 and 576 bonobos in the north and south sectors respectively. The estimate of 1,440 bonobos in the SNP compels a complete rereading of both methods used to estimate bonobo populations in the wild and a re-setting of conservation action priorities. These results provide insights for a new species-targeted approach for bonobo conservation in the SNP to be effective.

Resumen

Hay un total de 12 comunidades discretas de bonobos (Pan paniscus) en el Parque Nacional de Salonga (SNP, por sus siglas en ingles) fueron reportadas: 8 del sector del norte, y cuatro del sector del sur. Estas comunidades ocupan aproximadamente 1120km2, que representan solamente el 3% del area total del SNP. El estimado del tamano del nicho promedio de la comunidad rue de [approximately equal to]80km. Las distancias promedio eran de 57kin (SD+ 32) y 89km (SD + 70) en los sectores del norte y el suf respectivamente, pot ende puede que no ocurran interacciones inter-comunitarias. Ajustando las densidades publicadas pot Sabater-Pi y Vea (1990), Uehara (1988), (Van Krunkelsven et al. (2000, 2000a), y Kano (1992) para tomar en consideracion la fragmentacion y tamano del fragmento, la poblacion total de Salonga es de 1344 bonobos como minimo: 864 y 480 bonobos en los sectores norte y sur respectivamente. El estimado de 1344 bonobos en el SNP hace un llamado a la reevaluacion tanto de los metodos utilizados para estimar la poblacion silvestre de bonobos como una reestructuracion de acciones prioritarias de conservacion. Estos resultados nos proveen un mayor entendimiento para un nuevo enfoque al identificar especies, para que la conservacion del bonobo en el SNP sea efectiva.

Introduction

A fundamental aspect of conservation biology is describing the distribution of plants and animals (Sutherland 1999, 2000). Species distributions are often associated with availability of food (Coe 1984) or predation (Cowlishaw and Dunbar 2000), particularly for primates, and can capture the natural history of a given species (Darwin 1860). For conservation purposes, knowledge of the distributions of the species of interest is key to the allocation of conservation effort over time and space and is, together with species abundance, a determinant of effective and sound conservation strategy.

Bonobos (Pan paniscus) occur only in the Central Basin of the Congo River. It was the last species of great ape to be described, receiving full species status in 1933 (Reinartz and Inogwabini 2000; Kempf and Wilson 1997; Kingdon 1997; Kano 1992; Coolidge 1933). The distribution of the species was not described accurately until early 1980s when Kano (1979) undertook a survey in the region to document bonobo occurrence and threats to its conservation. Kano (1982, 1984) used both short field trips and interviews to assess their distribution. Salonga National Park (SNP) which encompasses about 36,000 [km.sup.2], was created in 1970 to protect the then supposed significant populations of bonobos and a great variety of other wildlife and the lowland tropical rain forest (IUCN 1992, Matuka 1975). However, previous range-wide surveys mistakenly reported that bonobos were absent from this massive wilderness (Kano 1979; Badrian and Badrian 1977). Meder et al. (1988) and D'Huart (1988) confirmed the presence of the species in the southern sector. It was only in the late 1980s that bonobos were reported in the northern sector near Watshi-Nkengo (D'Huart 1988) and confirmed by an independent scientific inquiry (Van Krunkelsven et al. 2000).

Since the confirmation of bonobo populations in both sectors of the park, several site-specific studies have been launched to study species abundance and distribution (e.g. Zoological Society of Milwaukee, Max Plank Institute, Lukuru Wildlife Research Project, Wildlife Conservation Society) and several others are being planned in the short and mid-term. Thus far, however, no single study has provided distribution of bonobos for the entire SNP, information that would guide conservation action and the implementation of new research programs. Bonobos occupy a maximum territory of 135,000 [km.sup.2] (Kortlandt 1995, Kano 1984) confined by two large river systems: the Congo-Lualaba and the Kasa'i-Sankuru (Kortlandt 1995). SNP sits at the heart of this range and represents approximately 27% of the total historical distribution of bonobos. Thus, providing ecological knowledge within the SNP is of paramount importance for conservation strategies for the species.

This paper presents the first data on the distribution of bonobos SNP gathered over the last eight years. This study provides geographical data on zones where bonobos proved to be present by field teams either by nests or by direct observation. We also discuss different patterns of bonobo distribution in the SNP in light of human pressures, food availability, physical lay of the land, and indications of recent and ancient forest history.

Study site

SNP (figure 1) is located in the central basin of the Congo River, in the Democratic Republic of Congo (DRC), and stretches over four provinces (Equateur, Bandundu, and the two Kasais), and is divided into two sectors, respectively called SNP North and SNP South. The habitat is predominantly mixed mature lowland tropical forest (Gautier-Hion et al. 1999; Evrard 1968) with large expanses of seasonally flooded and inundated zones. Characteristics of inundated zones are open understorey, with important tree communities composed of Uapaca heudelotii, Uapaca guineensis and Guibortia demeusi, Raffia sese, and Pandanus candelabrium (Inogwabini 2005; Gautier-Hion et al. 1999; Evrard 1968). Terra firma mixed mature forest includes indicative species such as Scorodophloeus zenkeri, Anonidium manii, Polyalthia suaveolens, Diospyros sp., etc. Patches of mono-dominant Gilbertiodendron dewevrei occur in small but unbroken stretches (Kortlandt 1995; Evrard 1968). Marantaceae stands (i.e. Haumania librechtsiana and Megaphrynium macrostachii) occur frequently in the understorey and sometimes constitute pure monospecific vegetation cover strata.

[FIGURE 1 OMITTED]

Forest altitudes vary between 300 and 700 m (Evrard 1968) and SNP is criss-crossed by a dense network of small rivers that feed the main systems of the Momboyo-Luilaka, the Salonga-Yenge and Lomela-Tshuapa (Inogwabini 2005) which all flow to the main Congo River. Mean annual rainfall oscillates between 2007 and 2106 mm (Griffiths 1972, Evrard 1968). The mean annual temperature is 24.5[degrees]C. Two dry seasons (long: July-September; short: January-February) and two rainy seasons (long: March-June; short: October-December) are characteristic of the region.

Materials and methods

Data presented in this study were collected using two different conventional methods: strict line transects and reconnaissance walk surveys. To document bonobo presence, evident bonobo signs such as nest sites, dung, food remains, knuckleprints and direct sightings were recorded. Nest sites were georeferenced with hand-held Garmin GPS units. The geographic coordinates of individual nest sites were plotted on a map using ArcView computer map package (Waters and Shockley 2000). Because previous studies indicated that a social unit of bonobos is a geographically stable community that ranges over 22 [km.sup.2] (Badrian and Badrian 1984), nest sites whose spatial distributions were clumped together within the range of [approximately equal to]5 km straightline were considered to be part of the same community. This range conforms to the study at Etate by the first author between 2000 and 2002, which indicated a radius of [approximately equal to]5 km for group range (unpublished data). To provide the spatial extent of geographical range of each community, geographic centers of nest site locations were plotted and then buffered by circles of 3 km radius, [partial derivative], the home range size provided by Badrian and Badrian (1984). A further buffer of 2 km was added to capture any need by bonobos to use the fringes of their habitats. Thus a radius to 5 km was used in the formula A = [pi][[partial derivative].sup.2], to obtain the total range width, assuming that the latter was circular. Community size estimates were obtained through multiplying range width by known densities. No densities were calculated in this study since sample sizes were often too small where conventional line-transects were used. We calculated mean distances between community ranges per sector by simply summing straight distances (obtained with ArcView distance tool) between centers of individual ranges divided by number of communities.

Results

A total of 15 discrete communities were found in SNP (Figure 1). There are nine communities in the northern sector: (1) Bolafa-Yongo, (2) Etate, (3) Ikolo, (4) Isanga-Imoto (5) Kinki-grotte, (6) Lokata, (7) Luputa, (8) Ngomba and (9) Yafala (figure 1). The six communities of the south are: (1) Boangola, (2) Beminyo, (3) Ila-Ediki, (4) Lokofa, (5), and (6) Luikotale (figure 1). The northern communities occupied a total area of [approximately equal to]640 [km.sup.2] in discrete ranges of maximum width [approximately equal to]80 [km.sup.2]. The four southern communities occupied a total area of [approximately equal to]320 [km.sup.2]. This makes a total area of [approximately equal to]960 [km.sup.2] of bonobo occupancy, merely [approximately equal to]3% of SNP. The mean distances between ranges were 57 km (SD [+ or -] 32) and 89 km (SD [+ or -] 70) in the northern and southern sectors respectively.

Estimates of bonobo density vary between [approximately equal to]0.4 individuals/[km.sup.2] (Sabater-Pi and Vea 1990; Uehara 1988) and [approximately equal to]3 individuals/[km.sup.2] (Van Krunkelsven et al. 2000a; Kano 1992) with a mean estimate of 1.2 for Salonga (Van Krunkelsven et al. 2000). Both the minimum and maximum densities were used to calculate population size. The use of 1.2 bonobos/[km.sup.2] is justifiable because this is the most recent, if not the only, estimate for the SNP. With that density estimate, the nine communities of the northern sector number a maximum of 864 bonobos while those of the southern sector 576 bonobos. This makes a total of 1,440 bonobos in the entire SNP. The minimum population size would be 346 and 230 individuals for the northern and southern sectors respectively.

Group sizes also vary across the bonobo's range, from 4 (Thompson 1997) to 15 individuals/group (Badrian and Badrian 1977). Using the upper limit, each community identified has between [approximately equal to]2 and [approximately equal to]6 groups within the 80[km.sup.2].

Discussion

We estimate that the 15 communities identified number only about 1,440 bonobos for the entire SNP. This is a striking result and compels a complete rereading of both methods used to estimate bonobo populations in the wild and a redrafting of conservation action priorities. On the methods front, the common practice has been to multiply density estimates by total area to obtain population estimates. Extrapolation using this conventional method would obtain a minimum of 14,400 (density estimate [approximately equal to] 0.4) and a maximum of 43,200 bonobos (density estimate [approximately equal to] 1.2) in SNP alone. Numbers obtained through the use of known communities and range size account for only 9% of the minimum or 3% of the maximum population estimated by flat-map calculations. Some authors (e.g. Van Krunkelsven et al. 2000) have cautioned against crude density estimates obtained in this way, as these estimates do not take into account ranging ecology and may inadvertently affect conservation effort by obscuring the reality on the ground. This paper shows that extrapolation of bonobo densities over large flat-area maps is inaccurate and should be viewed with caution. The study suggests that because bonobos have patchy distributions; the best estimators for their populations are nested estimators that take into account discrete communities discontinuously spread over the space. The only way to achieve this throughout the entire range is first to get accurate patch distribution maps, and get to census patch by patch, which is a laborious, time and money consuming process, and can come only from long-term field surveys. However, it remains the most sensible approach if we require precise population estimates.

Bonobos are known to occur in patches (Kortlandt 1995; Alers et al. 1992; Kano 1984) however reasons for this distribution feature are not yet clearly elucidated. Kortlandt (1995) argued that such a distribution resulted from major flooding zones within the core range, a sleeping sickness epidemic between 1895-1900, high hunting pressure, and forest exploitation. The bonobo populations described here have not been observed ranging in wet areas, although footprints were observed at the fringes of terra firma muddy soil both at Etate and Bolafa-Yongo. The fact that [approximately equal to] 50% of the northern sector of SNP is inundated during the heavy rainy seasons (Gautier-Hion et al. 1999; Evrard 1968) may help explain the paucity in bonobos in this sector. A reduced population in the southern sector, where the rainy season affects little of the terra firma forest strata, does however compel other explanations. The conservation community thought that the remoteness of this region would have had deterred heavy human incursion into SNP. In reality, the region has been exposed to massive human movements through a well-established trail system for many years (see Figure 1). During colonial times, trails such as Amateka-Bonima were used to extract copal and wild rubber from the forest and carry them to ports where they were loaded onto steamboats for exportation (Bom'oa Nkoso, personal communication). The trail network connects the deep forest of the Equateur Province to the mineral rich provinces of Kasai, and may have served as a commercial route for forest products for decades. Although no particular patterns of bonobo distribution in relation to these trails seem to emerge (see Figure 1) it is logical to infer that the actual distribution of bonobos in both sectors is indeed a result of human history in the region and that the trail network may have played a significant role in shaping it.

The conclusion that human history in the region may have played a role in shaping actual bonobo distribution remains valid even if one considers food availability as a determinant distribution factor. The bonobo food matrix comprises significant quantities of Haumania liebrechtsiana (Sommer et al. 2004; Malenky and Wrangham 1994; Idani et al. 1994; White 1992; Wrangham 1986; Badrian and Malenky 1984; Kano and Malavwa 1984, Kano 1983, Badrian et al. 1982; Horn 1980; Susman 1979) which is available year-round even during periods of fruit shortage which might otherwise limit group size and distribution. Haumania liebrechtsiana is found throughout both sectors of the SNP (Inogwabini et al. 2000) hence food availability would not explain a reduction in bonobo numbers.

Different communities of the bonobos in the SNP are under different human pressure levels. The community impacted most heavily is that of Ikolo (3 northern sector, Figure 1). In 2000, Ikolo was the most heavily poached region of the SNP, where 56 cable snares were removed for a sampling effort of 9km of straight line transects. Armed people were also reported to be active in this zone, apparently supplied with ammunition and automatic weapons by different fighting factions to provision troops on the front lines with bushmeat. Other bonobo communities exposed to high levels of poaching are those of Lokata and the Kinki-Grotte region, since the Institut Congolais pour la Conservation de la Nature (ICCN) has had only limited authority to enforce the law since the park's creation in 1970 (IUCN 1992). The Kitawalists, a neo-Africanist animist group, invested the zone to take refuge in the late 1960s after being defeated by the Congolese national army (IUCN 1992; D'Huart 1988). A further threat to bonobos residing in this region was the outbreak of the 1998 war as different troops alternatively occupied the strategic station of Lokalo, less than 30km from Kinki. Troops at Lokalo obtained food from the Kinki region of the park (Mulomba personal communication). In 2000, an infant bonobo captured from the zone of Lokalo was seized in the town of Boende (Inogwabini et al. 2000). The communities of Ngomba and Beminyo are also exposed to high hunting pressure, particularly with cable snares and arms. In 1997, Van Krunkelsven et al. (2000) came across a gang of poachers near the region of Ngomba; a single poacher had more than 300 bullets for automatic AKA machine guns. In 2001, the Zoological Society of Milwaukee (ZSM) research team discovered great numbers of snares and other evidence of poaching, such as elephant bones, hunting camps, and shot-gun cartridges, in the Beminyo region. The Conservator confirmed that patrols rarely reach this area far from headquarters, and it has been under siege by armed poachers (Bofenda, personal communication). Other communities are in better shape only because of their proximity to SNP's headquarters or patrol posts (e.g. Lokofa (4) in the southern sector, Figure 1) or, to more recently established scientific research bases (e.g. ZSM at Etate (2) in the northern sector, Max Planck Institute at Luikotale (5) in the southern sector, figure 1).

The mean distances between known communities are large. Using blood samples from captive bonobos, Reinartz (1997) and Reinartz et al. (2000) found that their geographical origins could be differentiated genetically. Long distances between communities may explain genetic differentiation, as discrete populations may not have interacted with their neighbors for long spans of time. Furthermore, the SNP river network separates the park into five broad blocks: (1) Lomela-Salonga, (2) Salonga-Yenge, (3) Yenge-Loile, (4) Luilaka-Lokolo, and (5) Lokolo-Lokoro (see Figure 1). These major rivers serve as natural barriers to bonobo interactions, implying that each sub-population in a river-limited block is a distinct conservation unit that may exhibit a specific ecological or genetic character (e.g. Eriksson et al. 2004). An illustration of this is that bonobos at Etate build [approximately equal to] 11% of their night nests on the ground, a habit that has not been documented in any other bonobo communities in the SNP.

The small size of the total population of bonobos in SNP, long distances between subpopulations and potential ecological and genetic impacts warrant a reshuffled species-targeted conservation strategy. Current conservation activities in the SNP operate from the park's six headquarters and advanced patrol posts located outside the park. Guards on patrol follow different itineraries based on river and trail systems with no precise objectives. This has to change if the protection of bonobos is the prime conservation objective in SNP as pledged in most official documents. Concretely, the strategy should focus on redeploying guard patrol posts and patrol itineraries to target locations with known bonobo populations. This means that 12 patrol posts have to be relocated nearer to known communities (figure 1). Guards posted here should be better trained to track animals in the forest and to document some important population parameters such as group size and numbers of offspring. As a consequence of this species-targeted strategy, the guard force's performance should be judged on precise indicators of their impact on the bonobo population to each post. By placing patrol post near bonobo communities, conservation aims are much more likely to be achieved. The ZSM has been testing this approach for the last five years in the Etate Region. Although the long-term benefits of this approach are not yet fully understood, the experience in Etate shows that bonobos have come closer to the trail network and can regularly be observed even though there is no habituation program. The backdrop of this strategy lies, however, in the sustainability of funding to support guards. Inogwabini et al. (2005) documented low numbers of guards, low salaries, relatively unqualified and ageing personnel for the entire protected area system in the DRC, a situation which is worse in SNP where geography constrains sound and sustained conservation efforts. Qualified personnel with material support is key to this species-targeted conservation approach, implying that sufficient resources need to be raised to train qualified guards and to sustain their action in the future. This is highly difficult in a country where insecurity waves are quasi-permanent but the future of small isolated bonobo populations depends on how well we succeed in securing resources to protect them physically. What is at stake is critically important, and we need to act.

Acknowledgements

Many thanks to the Institut Congolais pour la Conservation de la Nature (ICCN) for granting the permission to work in SNP under different organisations. Some data were collected while the first author worked for the Zoological Society of Milwaukee and another portion while both authors were carrying out elephant surveys for the CITES-mandated Monitoring of Illegal Killing of Elephants (MIKE) under the Wildlife Conservation Society. Thanks are extended to many of our field collaborators, principally: Lisalama Wema-Wema, Mafuta Ngama-Nkosi, Edmond Isomana Mputu, Bunda Bokili, Prince Lokima, Booto Nta, Mbenzo Abokome, Mbende Longwango, Matungila Bewa, and Dino Shwa. Thanks also to Liz Williamson for comments on the manuscript.

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Bila-Isia Inogwabini (1,2,3) Omari Ilambu (1)

(1) Wildlife Conservation Society

(2) Bp 15.872 Kin 1, Kinshasa Democratic Republic of Congo

(3) binogwabini@wwfcarpo or [e-mail]