Research and Conservation in the Greater Gombe Ecosystem: Challenges and Opportunities

Abstract

The study of chimpanzees in Gombe National Park, Tanzania, started by Jane Goodall in 1960, provided pioneering accounts of chimpanzee behavior and ecology. With funding from multiple sources, including the Jane Goodall Institute (JGI) and grants from private foundations and federal programs, the project has continued for sixty years, providing a wealth of information about our evolutionary cousins. These chimpanzees face two main challenges to their survival: infectious disease — including simian immunodeficiency virus (SIVcpz), which can cause Acquired Immune Deficiency Syndrome (AIDS) in chimpanzees — and the deforestation of land outside the park. A health monitoring program has increased understanding of the pathogens affecting chimpanzees and has promoted measures to characterize and reduce disease risk. Deforestation reduces connections between Gombe and other chimpanzee populations, which can cause loss of genetic diversity. To promote habitat restoration, JGI facilitated participatory village land use planning, in which communities voluntarily allocated land to a network of Village Land Forest Reserves. Expected benefits to people include stabilizing watersheds, improving water supplies, and ensuring a supply of forest resources. Surveys and genetic analyses confirm that chimpanzees persist on village lands and remain connected to the Gombe population. Many challenges remain, but the regeneration of natural forest on previously degraded lands provides hope that conservation solutions can be found that benefit both people and wildlife. Conservation work in the Greater Gombe Ecosystem has helped promote broader efforts to plan and work for conservation elsewhere in Tanzania and across Africa.

1. Introduction

Understanding the behavior and ecology of long-lived animals like chimpanzees requires long-term research, spanning multiple decades. Such projects provide important benefits for conserving wildlife and habitats (Wrangham & Ross, 2008). The first long-term study of chimpanzees (Pan troglodytes) began in 1960, when Jane Goodall arrived at Gombe Stream Game Reserve, Tanganyika Territory. After months of patient searching and watching, Goodall observed chimpanzees engaging in behaviors considered key steps in human evolution: eating meat, and making and using tools (Goodall, 1986). These and other discoveries enabled Goodall to acquire funding needed to extend research at Gombe from the initial five-month project to a truly long-term study, which is now in its 60th year.

Images and stories from Gombe presented in magazines, books, television, and film attracted a global audience. Gombe chimpanzees became the iconic wild chimpanzees, and to a large extent remain so for many, despite the bounty of information now being obtained from many other chimpanzee study sites. The worldwide attention gained by Goodall’s research led to the upgrading of Gombe from a Game Reserve to a National Park in 1968. Despite all this, the ability of Gombe’s chimpanzee population to survive remains uncertain. The park is small, and its chimpanzee population is small, relatively isolated from other chimpanzee populations, and subjected to major disease risks.

Gombe’s chimpanzees confront challenges that are faced by wildlife worldwide, as landscapes increasingly become modified to meet the needs of a rapidly growing human population. The human population of sub-Saharan Africa numbered around 227 million when Goodall first came to Gombe, and by 2050 is expected to exceed 2 billion: a nearly 10-fold increase (Suzuki, 2019). If effective conservation action is not taken, Africa’s wildlife populations will decline steeply, with many species becoming extinct (Tilman et al., 2017). Within protected areas, some species may be unable to persist without intensive interventions to treat infectious disease, including infections originating in humans and domestic animals. Moreover, parks alone will not be sufficient to ensure the conservation of large, wide-ranging species. A survey of large mammals in protected areas across Africa found a 59% decline in population abundance from 1970 to 2005 (Craigie et al., 2010). Effective conservation requires not only conserving populations within protected areas, but also finding solutions that enable wildlife and people to coexist outside of protected areas.

Here, we begin with an overview of research at Gombe. Next, we examine population dynamics of Gombe’s chimpanzees, and then discuss the two major issues affecting prospects for their long-term survival: health and habitat. In working to promote conservation in and around Gombe, we have learned lessons that may be applied widely.

2. Research at Gombe

2.1. Study Site

Gombe National Park is located in northwestern Tanzania (Figure 1). Established as a Game Reserve in 1943 (Thomas, 1961), this narrow park covers 35.69 km² of land, and (since 2015) 20.72 km² of Lake Tanganyika. Mountains rise from the lakeshore (766 m.a.s.l.) to peaks (1,300–1,623 m.a.s.l.) along the eastern boundary (Pintea et al. 2012). Ridges divide the park into 15 major valleys. Vegetation includes evergreen forest in the valleys, semi-deciduous forest and vine tangle on the slopes, open woodland on the ridges, and montane grassland at higher elevations. The Greater Gombe Ecosystem (GGE) is a geographical area defined by stakeholders as part of the Conservation Action Planning process in 2005 (Pintea et al., 2012). The Jane Goodall Institute adopted the term GGE in analogy with the Greater Yellowstone Ecosystem (Keiter & Boyce, 1994), as part of an effort to recognize that Gombe is part of a larger system and to integrate conservation efforts in the region. It includes current and historic chimpanzee habitat inside and outside the park, encompassing Gombe National Park and the lands of 27 nearby villages, which together cover approximately 640 km². Conservation efforts on village lands center on facilitating and building capacity using Tacare, JGI’s community-driven approach to conservation, to develop and implement village land use plans, which include a network of village forest reserves connected to Gombe.

Figure 1.

Gombe National Park and its surroundings, including signs of chimpanzees outside the park. The purple polygon north of Gombe encloses the locations of chimpanzee sightings, nests, and genetic samples along the Gombe-Burundi Ridge. Blue circles indicate other evidence of chimpanzee presence outside the park, including nest locations within the Kwitanga Prison forest east of Gombe, and crop-raiding excursions by Mitumba chimpanzees immediately north of the park, and nests found on village land between Gombe and Kwitanga.

Three chimpanzee communities live in the park: Mitumba, Kasekela, and Kalande. Chimpanzees range throughout the park, but spend most of their time foraging for ripe fruit in the evergreen forest and woodlands (Foerster et al., 2016b). Other primates in the park include olive baboons (Papio anubis), red colobus monkeys (Piliocolobus tephrosceles), red-tailed monkeys (Cercopithecus ascanius schmidti), blue monkeys (C. mitis doggetti), and vervets (Chlorocebus pygerythrus). As part of the Albertine Rift, Gombe lies within a global biodiversity hotspot (Plumptre et al., 2007), which includes an exceptionally diverse population of cichlids and other aquatic species endemic to Lake Tanganyika (Salzburger et al., 2014).

2.2. Major accomplishments

Six decades of research at Gombe have yielded a wealth of scientific findings, with nearly 300 scientific publications (Figure A1). We cannot hope to do justice to this diverse body of work here. The long duration of the study has yielded many discoveries that would not have been possible without long-term data (Wilson, 2012). Research methods pioneered at Gombe have inspired similar approaches at other field sites, contributing to a broadening comparative perspective for understanding behavioral diversity across chimpanzees and bonobos (Boesch et al, 2010). Amply fulfilling the hopes of Goodall’s mentor, paleoanthropologist Louis Leakey, research at Gombe has played a prominent role in inspiring and testing hypotheses about human evolution (Wilson, in press). The details of Goodall’s early years at Gombe are familiar to many from accounts in popular books (van Lawick-Goodall, 1971; Goodall, 1990), which describe the distinctive personalities of individuals such as David Greybeard — the first chimpanzee that she saw using tools — and Flo, the aging matriarch. Goodall produced the first detailed accounts of chimpanzee diet, hunting, tool use, communication, mother-offspring interactions, and social life, summarizing findings from the first decades of the study in her magnum opus: The Chimpanzees of Gombe: Patterns of Behavior (Goodall, 1986).

Goodall and her team have ensured that the basic data collection methods established by the early 1970s have continued to the present. Starting in the 1990s, Anne Pusey led the digitization of the paper data into a computer database, which now makes possible the analysis of many decades’ worth of observations. Because chimpanzees grow and reproduce slowly, it has taken all of these years to acquire a basic understanding of chimpanzee life histories, including development of sex differences (Lonsdorf, Markham, et al., 2014), age of weaning (Lonsdorf et al., 2019), consequences of being orphaned (Stanton et al., 2020), age of first reproduction (Walker et al., 2018), dispersal (Walker & Pusey, 2020), reproductive cessation (Alberts et al., 2013), causes of death (Williams et al., 2008), and after death, how life history events mark the skeleton (Kirchhoff, 2019). Studies have clarified that males and females differ strikingly in their lifetime patterns of dominance rank (Foerster et al., 2016a), but high dominance rank provides reproductive benefits for both females (Pusey et al., 1997; Jones et al., 2010) and males (Wroblewski et al., 2009). Females compete over access to individual core areas (Murray et al., 2006), while groups of males compete over group feeding territories (Williams et al., 2004). Participating in coalitionary aggression increases reproductive output for males (Gilby et al., 2013). Lethal aggression occurs within and between communities at Gombe and most other sites (Wilson et al., 2014).

After six decades of study, chimpanzees continue to surprise researchers, such as when Gremlin “kidnapped” her daughter Gaia’s infant (Wroblewski, 2008). However, most new discoveries now involve the work of large interdisciplinary teams using long-term datasets, often in conjunction with new technologies that provide key insights, on scales from molecules (genetics, hormones) to landscapes (Geographic Information Systems and high-resolution satellite images). Such work has produced new findings in genetics (Prado-Martinez et al., 2013; Wroblewski et al., 2013), pathogens (Bakuza & Nkwengulila, 2009; Gillespie et al., 2010; Keele et al., 2009), hormones (Emery Thompson et al., 2005; Markham et al., 2014), nutrition (O’Malley & Power, 2012), skeletal morphology (Kirchhoff, 2019), life histories (Alberts et al., 2013; Bronikowski et al., 2016; Walker et al., 2018; Williams et al., 2008), development (Lonsdorf et al., 2020; Murray et al., 2016; Stanton et al., 2020), social behavior (Feldblum et al., 2014; Gilby et al., 2006; Pusey & Schroepfer-Walker, 2013; Foerster et al., 2016a), cultural patterns (Lonsdorf et al., 2005; Musgrave et al., 2020; O’Malley et al., 2012, Whiten et al., 1999), ecology (Adamescu et al., 2018; Foerster et al., 2016b; Murray et al., 2006), and remote sensing (Jantz et al., 2016). New techniques combined with the rich datasets on behavior and demography continue to open new opportunities to elucidate the behavioral ecology, ontogeny, endocrinology, demography, population biology, and disease ecology of this endangered species. Such new technology has enabled researchers to settle long-standing questions, and to ask new questions undreamt of 60 years ago.

Multiple long-term study sites now exist of chimpanzees and other primates. Researchers trained at Gombe have founded a number of these sites, including Richard Wrangham (Kibale Chimpanzee Project: Emery Thompson et al., in press) and Mark Leighton (Gunung Palung Orangutan Project: Knott et al., in press). Gombe research remains exceptional in the length of the study; the level of detail on individual life histories; and the scale of community-centered conservation efforts undertaken outside the park.

2.3. Funding and Organization

Grants from individual donors and foundations such as the National Geographic Society supported the first years of Gombe research. As Goodall’s operation grew, it became increasingly challenging to ensure a steady supply of grant support. Goodall therefore founded the Jane Goodall Institute (JGI) in 1977, which continues to provide core funding for the project. Research grants from public and private foundations provide additional support, including the National Institutes of Health (NIH), the National Science Foundation (NSF), private foundations, and associated universities.

Tanzanians have become increasingly involved in scientific leadership at Gombe. Four Tanzanians have earned Ph.D.s through research at Gombe (Kamenya, 1997; Mjungu, 2010; Bakuza, 2012; Chuma, 2020). Kamenya and Mjungu subsequently served as directors of the project. Two Tanzanians trained at Gombe (Sood Ndimuligo and Wilson Kimaro) are currently conducting doctoral research. Four Tanzanians have served as health project managers (Jared Bakuza, Jane Raphael, Iddi Lipende, and Dismas Mwacha).

JGI employs a full-time research team at Gombe of about 50 employees, including senior scientists (Mjungu and Collins), a veterinarian (Mwacha), and field researchers specializing in chimpanzees, baboons, other monkeys, and botany. Chimpanzee researchers work in teams to conduct focal follows of individual chimpanzees (usually from dawn to dusk), and also conduct observations of mothers and infants and adolescent females, monitor chimpanzee health, collect fecal and urine samples, and carry out monthly phenology transects focused on plant species important in the chimpanzee diet. Research involves collaboration with scientists at many different institutions. To coordinate these efforts, the Gombe Research Consortium was established in 2018, consisting of research administrators from JGI (Collins, Mjungu, and Pintea) and principal investigators based elsewhere (Detwiler, Gilby, Lonsdorf, Murray, Pusey, and Wilson).

3. Chimpanzee Population Dynamics

Chimpanzees are the iconic species of Gombe and the focus of conservation efforts. The size and growth rate of the park’s chimpanzee population thus serves as a measure of the success of these efforts. In the 1960s, we estimate that 120–150 chimpanzees lived in Gombe (Pusey et al., 2007), based on the number of individuals identified in Kasekela, plus perhaps 30–50 and 30–40 individuals in Mitumba and Kalande, respectively. Both the Mitumba and Kalande communities presented a substantial intergroup threat to Kasekela into the 1980s (Goodall, 1986), and so are likely to have had similar numerical strength to Kasekela. In 1969, C. Gale identified more than 20 individuals in Kalande and estimated the total community to be 40 individuals (Rudicell et al., 2010). Additional chimpanzees may have lived in a “Rift Community” east of the park (Pusey et al. 2007; Pintea et al., 2012). We have obtained reliable estimates of Gombe’s total chimpanzee population since 2002. Figure 2 shows the annual population size based on the number of individuals known to be alive at the start of each year, for years in which either all individuals were individually recognized by observers (Mitumba and Kasekela communities) or were known to exist through observation or genotyped fecal samples (Kalande community). The Kasekela community contained a median of 52 individuals (range: 39–62 individuals; N = 55 years). By 1973, approximately 14 individuals separated from Kasekela, forming the Kahama community (Goodall, 1986; Feldblum et al., 2018). Kasekela males then attacked and killed at least five males and one female from Kahama (Goodall, 1986), resulting in the Kahama community’s demise in 1977. The remaining females and young emigrated to other communities. The Mitumba community, habituated since 1996, contained a median 25 individuals (range: 20–29; N = 25 years). The Kalande chimpanzees have been monitored continuously since 1999, with collection of fecal samples for genetic monitoring since 2001. A conservative estimate, including only visually confirmed individuals and estimates from genotyped samples, yields a minimum of 19 individuals in 2002 (Figure 2). By 2020, only 5 individuals remained, including one adult male, Kazi, who is the son of the only adult female, Kati, who has been mating with Kasekela males to produce her offspring (Walker et al., 2017).

Figure 2.

Minimum population estimates for chimpanzee communities living within Gombe.

The recent total population of 89–92 chimpanzees (2002–2020) represents a substantial decline from the 120–150 estimated to have lived in Gombe in the 1960s. At that time, the Mitumba and Kalande community ranges likely extended beyond current park boundaries (Pusey et al., 2007). In the subsequent decades, people cleared much of the forest on village land for farms, reducing the carrying capacity of the Greater Gombe Ecosystem for chimpanzees and other wildlife (ibid.). Within the park, however, forest cover increased, due in part to successful suppression of fire by park authorities (Pintea et al., 2012). Whether the park’s current population is at carrying capacity, or has been kept below carrying capacity by factors such as disease, remains unknown.

The consistent presence of approximately 90 chimpanzees in Gombe since 2002 might suggest the population is now stable. However, based on life history data for 133 males and 155 females from Mitumba and Kasekela, Bronikowski and colleagues (2016) estimated the basic reproduction number, R₀, to be 0.745 (95% CI: 0.537–0.998). This indicates that each female produces an average of less than one breeding daughter, resulting in population decline. In contrast, the six other primate species in this study had growing populations (e.g., mountain gorillas, Gorilla beringei, R₀ = 1.918 (95% CI: 1.541 – 2.365; Brownikowski et al., 2016). Whether the low R₀ for Gombe results mainly from high mortality or low fertility has not been determined. Gombe chimpanzees have similar interbirth intervals to chimpanzees at other study sites (Emery Thompson, 2013) and age-specific mortality rates that are in the middle range (Hill et al., 2001; Muller & Wrangham, 2014; Wood et al., 2017). SIVcpz infection likely plays a major role, as it increases mortality risk and reduces fertility (Keele et al., 2009). Despite the low value for R₀, the Kasekela and Mitumba communities exhibited positive mean annual growth rates (Kasekela: mean = 0.27%, 1966–2020); Mitumba: mean = 0.81%, 1996–2020). This net growth likely results from immigration, both from females and their offspring leaving the Kalande community (mean annual growth rate = −6.12%, 2002–2020), and from communities outside the park.

4. Health

To prevent the decline of Gombe’s chimpanzee population, the death rate must be reduced. Major causes of death for chimpanzees include predation, intraspecific violence, and infectious disease (Williams et al., 2008). Gombe no longer has large predators such as leopards (Panthera pardus), and the park is well protected, with few cases of poaching. Chimpanzees sometimes kill one another, but little can be done to prevent such violence. The one cause of death we can hope to reduce is thus infectious disease. Such diseases occur naturally, but human activities can increase the risk of disease transmission to apes (Köngden et al., 2008, Negrey et al., 2019). Much recent work at Gombe has involved efforts to identify and reduce sources of disease.

4.1. Health monitoring

Efforts to monitor health systematically at Gombe began in 2000 (Lukasik-Braum & Spelman, 2008), and now constitute a comprehensive program (Lonsdorf et al. 2006, 2018; Travis et al. 2008). Each day, observers conducting focal follows also note clinical signs (e.g., coughing, diarrhea, wounds), both for the target of their follow, and for any individual observed ill. In addition, the team conducts weekly health censuses to record whether each individual was seen, and whether any clinical signs were observed (Lonsdorf et al. 2006, 2018). Using these data, Wolf and colleagues found that the observation of at least two individuals with respiratory symptoms in a given week reliably signaled the start of a respiratory outbreak (Wolf et al. 2019).

Respiratory disease appears to be the most common cause of death from illness for Gombe chimpanzees, with 48% of chimpanzees inferred to have died from illness reported to exhibit respiratory symptoms (Williams et al., 2008). Determining the specific pathogen responsible for any particular set of symptoms, however, remains challenging. For such diagnosis, direct sampling of blood and/or tissues is ideal. However, such invasive sampling is rarely conducted on wild apes, as darting is disruptive and dangerous (Travis et al., 2008). Even when direct sampling is possible, conclusive diagnosis can prove elusive. For example, in 2005, adult male Faustino was found in extremely poor health, unable to move his hind limbs (Lonsdorf et al., 2014). Veterinary intervention, including treatment with antibiotics and intravenous fluids, restored his mobility. Analysis of blood and fecal samples identified pathogens, including an adenovirus, but failed to provide a definitive diagnosis (ibid.).

Due to the risks involved in direct sampling, the project mainly uses noninvasive methods, such as testing fecal and urine samples, and tissue samples from dead individuals. Gillespie and colleagues have identified over 30 species of helminths, protozoans, bacteria and viruses from chimpanzee samples (Gillespie et al. 2010, Parsons et al. 2014, Parsons et al. 2015, Deere et al. 2019), some of which cause illness. Terio and colleagues implemented a necropsy and histopathology protocol, and found that some chimpanzees die from oesophagostomiasis, caused by a parasitic worm, and AIDS (Keele et al., 2009; Terio et al., 2011, 2018).

The discovery that some chimpanzees at Gombe are naturally infected with SIVcpz — the immediate precursor of HIV-1 — played a key role in determining that the AIDS pandemic originated in human contact with chimpanzees and gorillas, likely through hunting and butchering apes for the bushmeat trade (Sharp & Hahn, 2011). When SIVcpz infection was first reported from Gombe (Santiago et al., 2002), scientists generally believed that the virus did not cause illness in chimpanzees. However, Hahn and colleagues found that infected chimpanzees can develop CD4+ T cell depletion, AIDS-like immunopathology, and a 10–16 fold increased risk of death (Keele et al., 2009; Terio et al., 2011). Moreover, SIVcpz infected females had lower birth rates and higher infant mortality than non-infected females (Keele, 2009). The community with the highest prevalence of SIVcpz infection, Kalande, suffered a catastrophic decline (Rudicell et al., 2010). Although SIVcpz infection can be effectively treated with antiretroviral therapy (Barbian, 2017), such an intervention is currently not feasible in wild populations. Out of 173 chimps sampled at Gombe over the past 20 years, 36 (20.8%) have tested positive for SIVcpz, and the infection persists in the population (Figure A2).

Assessessing the sources of pathogens remains challenging. Recent decades have seen a growing appreciation of the extent to which human health interfaces with the health of other animal populations. Disease transmission can occur between and among humans, domestic pets, livestock and wildlife. To take these interconnections into account, the health monitoring project has expanded to include a “One Health” approach, integrating diagnostic surveillance for Gombe’s chimpanzees and baboons, and examining links with people and domesticated animals (Parsons et al., 2014, 2015; Deere et al., 2019). Parsons and colleagues (2014) found substantial spatial overlap between goats, sheep, dogs, chimpanzees and baboons along the park’s edges. Fecal samples from humans, chimpanzees, and baboons found that individuals in all three species were infected with a human pathogen, Cryptosporidium hominis (Parsons et al. 2015).

Given the risk that humans can transmit infections to chimpanzees, particularly respiratory viruses to which chimpanzees have not developed immunity, precautions must be taken to reduce the risk of transmission. Homsy (1999) drew attention to these risks and recommended precautionary measures. In 2000, following the death of two chimpanzees during a respiratory outbreak in Kasekela, researchers closed the banana feeding station and worked with park staff to follow Homsy’s (1999) recommendations (Collins 2003, Pusey et al., 2008). Protocols stipulated a minimum distance of 7.5 m for researchers, and 10 m for tourists, who (due to recent travel) are more likely to carry respiratory viruses to which chimpanzees have not yet developed immunity. Tourist visits are restricted to no longer than one hour, and in groups no larger than six people. Visiting researchers are asked to complete a 7-day quarantine before following chimpanzees (Collins 2003). Since 2017, observers have been required to wear face masks when with chimpanzees. In addition, because chimpanzees often travel through areas where staff live, GSRC moved staff families out of the park, built wire mesh cages around the front of staff houses, and introduced a shift system to reduce the number of staff in the park. Efforts have been made to improve sanitation, including running water and flush toilets.

Many challenges remain. The lack of diagnostic tools available on site, the limited infrastructure for keeping samples cold in transit, and the long delay between sample collection and testing, are the most formidable barriers. However, a newly constructed on-site laboratory funded by the National Science Foundation has improved our diagnostic capacity. Efforts are underway to build a mobile genome sequencing lab and develop local capacity in partnership with Microsoft’s Project Premonition. The IUCN Best Practices Guidelines for Great Ape Health (Gilardi et al. 2015) provide further guidance for protecting Gombe’s wild primates from health-related threats. The COVID-19 pandemic has reemphasized these threats. Extreme precautions, including the temporary suspension of research, have been employed to safeguard the future of Gombe’s wildlife (Gillespie et al. 2020). Additional measures, such as providing treatment during outbreaks, may be needed. Outside the park, partnerships must be expanded to promote ecosystem health more broadly. Finally, to ensure the conservation of wildlife in developing countries, it is critically important to build local capacity for veterinary health. To date, the project has trained three Tanzanian veterinarians specialized in great ape health, and has provided advanced training in laboratory and research techniques to several other staff.

5. Habitat

Small, isolated populations face increased extinction risk (Davies et al., 2000), and Gombe is a small park. Comparison of Landsat MSS and Spot 4 satellite images combined with historical aerial photos of village lands surrounding Gombe revealed that between 1972 and 2003, 64% of the forests and woodlands potentially used by chimpanzees outside the park had been converted to farmland and other land uses, making Gombe an island of natural habitat in a human-dominated landscape (Pintea et al., 2012). Some larger mammals, including leopards and buffalo (Syncerus caffer), have already disappeared from Gombe. To prevent chimpanzees from disappearing as well, connections to other populations must be restored and maintained.

Because the land surrounding Gombe is occupied by densely populated villages, expansion of the park is not feasible. Nonetheless, steps have been taken to restore natural habitat on village lands through JGI’s community-driven conservation approach, seeking to find solutions that benefit both people and wildlife. Reforestation can provide important ecosystem services: stable watersheds with clean water, and sustainable supplies of firewood, timber, honey, and traditional medicines. Deforestation degraded these resources, resulting in barren hillsides, erosion, and landslides. To help communities find solutions, JGI initiated the Lake Tanganyika Catchment Reforestation and Education Program (TACARE) in 1994, with funding from the European Union (Collins & Goodall, 2008). A team led by Emmanuel Mtiti went into the villages, listened to the villagers’ needs, and developed programs intended to help both people and wildlife habitats, such as promoting woodlots, planting trees, and providing education about agroforestry and healthcare.

While TACARE succeeded in many respects, its efforts to promote reforestation could not keep pace with rapid human population growth. Analysis of aerial photographs and satellite images indicated that the deforestation rate in areas important for chimpanzees doubled from 87.5 ha/year (1972–1991) to 171 ha/year (1991–2003) (Anderson et al. 2004). Starting in 2005, JGI therefore adopted a new approach focused on implementing Tanzanian policies that empowered village governments to manage their land, with support from the United States Agency for International Development (USAID). Village land use planning provided a mechanism to set aside land to restore ecosystem services while securing land tenure for local communities, clearly defining the boundaries of the park, village land, and village forest reserves. These plans were implemented with full involvement of government and community stakeholders (Pintea et al., 2016). JGI did not direct the land-use planning, but instead facilitated it by providing financial, logistic and technical support, including access to maps and geospatial tools to record and manage spatial data. The planning process followed six steps and required villagers to settle any existing land disagreements and agree on village boundaries and how their land should be used to meet specific human livelihood needs and conservation objectives. By 2009, 13 villages had completed their land-use plans, assigning 26% of their village area (96.9 km²) to Village Land Forest Reserves (VLFRs) (Pintea et al., 2012), which include an area now designated by the government as the North of Gombe Wildlife Corridor. Covering 2.7 times as much land as the park’s 35.69 km², the VLFRs represent a major step towards securing the future for Gombe’s chimpanzees.

The VLFRs are patrolled by Village Forest Monitors, using GPS enabled smartphones and tablets to collect data and share it with local government and JGI staff. Analysis is shared back to inform actions at the district and village level in collaboration with the district government, TAWIRI, TANAPA and other local decision makers. Major conservation issues are discussed at multiple levels of decision making, from village, ward, and district to national levels. Forest regeneration has occurred across much of this area. Where tree root systems remained in areas cleared for subsistence farming, trees have been able to regenerate quickly. A field assessment of the extent to which biodiversity restoration has occurred in reforested areas is currently underway.

Surveys have confirmed that chimpanzees live in VLFRs 15–20 km north of Gombe (Figure 1). Analysis of fecal samples collected 2015–2019 confirmed the consistent presence of at least 6 chimpanzees; four were infected with SIVcpz (Hahn, unpublished data). Viral and host genetic similarities with two Gombe females indicate that females have dispersed between this population and Gombe (ibid). However, surveys also revealed extensive tree cutting, clearing land for crops, and new houses within VLFRs. New actions and resources are needed to enforce village land use plans in this area.

Chimpanzees also may persist 15 km east of Gombe in Kwitanga Forest, a roughly 25 km² expanse of woodland managed by Kwitanga Prison. Ndimuligo (2008) found evidence of approximately 15 chimpanzees in Kwitanga, and some chimpanzees may still remain there (Ndimuligo, unpublished data). Densely settled village land separates Gombe from Kwitanga, but chimpanzee nests found midway between the sites suggest they could still be linked (Figure 1).

Restoring connections with chimpanzee populations beyond the Greater Gombe Ecosystem remains a challenge. An unknown number of chimpanzees persist across the border in Burundi, and chimpanzees potentially travel between Burundi and Tanzania. Approximately 2,500 chimpanzees live in Tanzania (TAWIRI, 2018), including 500–700 in Mahale Mountains National Park, 150 km south of Gombe. Most of the remaining chimpanzees inhabit the Masito-Ugalla Ecosystem, over 60 km southeast of Gombe (Piel et al., 2015). JGI has worked extensively in this area to facilitate village and district land use plans, resulting in over 6,465 km² of new protected areas, including local authority forest reserves managed at the District level (5,222 km²), and a variety of village forest reserves (e.g., private forests, woodlots, wildlife reserves, etc.) managed by the local communities (1,243 km²; Figure 3). As a result, the proportion of chimpanzee range in Tanzania protected by law increased from 9% in 2005 to 43% in 2019. In 2018, the Government of Tanzania designated the Gombe-Masito-Ugalla UNESCO Biosphere Reserve, creating new opportunities for conservation.

Figure 3.

The Gombe-Masito-Ugalla Biosphere Reserve, showing the locations of different protected areas in the region. The village land forest reserves and local authority forest reserves shown here have all been established since 2005 through a participatory land-use planning process facilitated by the Jane Goodall Institute. The brown polygon enclosing known chimpanzee range and corridors was developed as part of the Tanzania Chimpanzee Conservation Action Plan (TAWIRI 2018).

6. Conclusions

Research at Gombe provided the first detailed descriptions of chimpanzee behavior and ecology in the wild. Sixty years on, the project continues to provide new insights into the lives of chimpanzees. Research has promoted the conservation of chimpanzees, and by protecting the chimpanzee habitat, benefits many other species. Nonetheless, the chimpanzee population has declined substantially. The survival of chimpanzees at Gombe requires improvements to their health and habitat.

Systematic health monitoring has identified pathogens and patterns of infection. The discovery of SIVcpz in Gombe contributed to our understanding of the origins of human AIDS. This virus poses a major challenge, as we currently cannot treat infected chimpanzees. We can, however, make efforts to reduce the risk of transmitting other diseases from people to chimpanzees. Sanitary measures at Gombe are not as strict as at some other sites, such as at Taï National Park, Côte d’Ivoire. Nonetheless, Patrono et al. (2018) found that chimpanzees at Taï became infected with a human coronavirus that was genetically identical to a virus found in a researcher who had gone through quarantine and was asymptomatic. So even a strict quarantine system does not prevent all infections. Tourists help pay for the park, and tourism can educate the public and encourage support for conservation. We urgently need to revisit measures needed to make research and tourism safe for apes.

It is worth noting, however, that the community with the least contact from research and tourism — Kalande — suffered the most dramatic decline. Multiple factors contributed to Kalande’s decline, including high prevalence of SIVcpz (Rudicell et al., 2010), and the killing of at least one, and perhaps up to six, Kalande chimpanzees by people in the years 1998–2002 (Pusey et al., 2007). The constant monitoring of the Mitumba and Kasekela chimpanzees likely provides important protection from poachers.

The decline of Gombe’s chimpanzees stands in stark contrast to the robust growth of the Virunga mountain gorilla population. Robbins et al. (2011) found that “extreme conservation measures,” including intensive veterinary intervention, were responsible for the higher growth rate of gorillas in habituated groups. While Gombe chimpanzees face different circumstances from mountain gorillas — chimpanzees reproduce more slowly than gorillas, and mountain gorillas are not infected with SIVcpz — more direct veterinary interventions may be needed to ensure the survival of chimpanzees at Gombe. As with Gombe chimpanzees, the gorilla groups most exposed to human contact have experienced higher growth, indicating that the benefits of constant monitoring can offset the risks of exposing apes to human diseases.

Deforestation on village lands surrounding Gombe reduced the carrying capacity for chimpanzees and other wildlife, and threatened to isolate Gombe from other chimpanzee populations. The establishment of a network of Village Land Forest Reserves promises to restore habitat and protect chimpanzees still living on village land. With further measures, it may become possible to restore connections to other chimpanzee populations in Burundi and Tanzania.

Conservation activities potentially impose costs on people, particularly those who are already marginalized. Gombe, for example, is located in a low-income region of a developing country, in an area with many refugees fleeing conflict in neighboring countries. Land reserved for parks could instead be inhabited and used by people for purposes such as farming, logging, and grazing. People living near wild animals face risks from crop-raiding and predation. Chimpanzees at Gombe and other sites sometimes raid crops, and on rare occasions, attack children (Hockings et al., 2015). At the same time, however, conservation can provide many benefits: income from work associated with tourism and research; protection of watersheds; and protection of species that provide services such as pollination, seed dispersal, and pest control. Wild species may be valued for food, medicine, or other uses, or may be valued in their own right. However, the people who place the highest value on wild animals and places often live far from protected areas, and do not directly incur the costs of conservation (Green et al., 2018). For conservation to succeed, a critical mass of people must perceive that conservation activities produce net benefits. An ethical approach to conservation seeks to find solutions that benefit both people and wildlife, and that takes special care to minimize impacts and maximize benefits to the people most likely to incur the costs of conservation. Engagement with local communities is essential, both to educate people about benefits that might not otherwise be obvious (e.g., watershed protection), and to work with local communities to find mutually beneficial solutions. Conservation work in the Greater Gombe Ecosystem has provided a model for chimpanzee conservation across Africa. JGI adapted the principles underlying TACARE for its “Tacare” conservation programs in countries including Uganda, Democratic Republic of Congo, Republic of Congo, and Senegal (janegoodall.org). This approach seeks to address the threats to chimpanzee populations and habitats by ensuring that local people and institutions own and drive the conservation process in their landscapes. This includes engaging and listening to people’s needs and priorities and facilitating village land use plans. When these local conservation efforts are informed by spatially explicit conservation visions and relevant data, there is an opportunity to connect national and global conservation goals with what people need locally. Many challenges remain, but the regeneration of natural forest on previously degraded lands provides hope that conservation solutions can be found that benefit both people and wildlife.

Highlights.

• Sixty years of chimpanzee research at Gombe National Park, Tanzania, have provided a wealth of information about our evolutionary cousins

• Chimpanzees at Gombe face two main challenges to their survival: infectious disease and the deforestation of land outside the park.

• The health monitoring project at Gombe has improved understanding of chimpanzee and ecosystem health

• Participatory village land use planning has resulted in a network of Village Land Forest Reserves near Gombe

• Regeneration of natural forest on previously degraded lands provides hope that conservation solutions can be found that benefit both people and wildlife.