Why the Chimpanzees of Gombe National Park Are in Jeopardy

Gombe National Park, a 35-square kilometer park in Kigoma Region in northwestern Tanzania, is most popularly known as the place where Jane Goodall conducted her pioneering research on chimpanzees beginning in the 1960s (see map). But over the past four decades, the chimpanzee population of Gombe has dropped from about 150 at the time Goodall arrived to approximately 90 today, while human population growth in the region and specifically around the park has soared.1

Tanzania and Gombe National Park

The reasons for the drastic decline in Gombe’s resident chimp population are well-known to scientists and park personnel: too little habitat and too much disease. Either habitat loss or regularly occurring disease outbreaks can precipitate a significant population decline for any particular species—but when both come into play, the results can be especially devastating.

It is now largely in the hands of humans—park staff, researchers, rural development professionals, tourists, and local communities—to conserve Kigoma’s remaining forests and to create and maintain a healthy environment so that the chimpanzees of Gombe might survive the 21st century.Population Growth and Human Activity Put Pressure on the Park

Kigoma Region, which is just over 37,000 square kilometers in size, has a human population of 1.7 million. A large immigrant population—mainly refugees from Burundi and Democratic Republic of Congo—has combined with Kigoma Region’s very high fertility rate to produce a regional population growth rate of 4.8 percent per year—the highest regional growth rate in Tanzania, which has an overall growth rate of 2.4 percent.2

This high population growth has led to a significant reduction in the amount of forested land around Gombe National Park, as people clear the land to make way for houses and farms. The practice of slash-and-burn agriculture (known locally as “shifting cultivation”) and cutting trees for making charcoal and firewood has also contributed to the deforestation of Kigoma.

“Shifting cultivation is the biggest environmental threat to the region,” says Aristide Kashula, a forester with the Jane Goodall Institute in Kigoma. “We have been working with farmers in 24 villages around Gombe to encourage the adoption of agroforestry approaches to farming, as well as teaching them to contour their fields and plant native grasses to combat soil erosion. But we are still struggling with deforestation.”

In fact, the park—always considered tiny compared to the other protected areas of Tanzania —is now described by Gombe-based researchers as an “island” of biodiversity, bordered by Lake Tanganyika on the west and by human settlements on its northern, eastern, and southern boundaries. Because of its small size, the bordering forests outside the park were once critical in providing “spill-over” habitat space for chimpanzee and other large mammal species. Without these forests to support them, large mammals such as lions and buffalo have already disappeared from the area completely, and the shrinking habitat is now causing problems for the remaining chimpanzees.

Gombe’s Chimpanzees Under Particular Threat

While other primates (such as baboons and red colobus, red tail, and blue monkeys) have managed to thrive in Gombe, chimpanzees have not. Their larger body size puts them at a disadvantage in a restricted habitat, because they must consume more calories (and thus more food) to grow and maintain their weight. Furthermore, chimpanzees’ more specialized physiology means that they cannot eat grass, stems, or unripe fruit—things that baboons and other monkeys are able to eat.

As food availability decreases and competition for it increases, chimpanzees and other animals have become more likely to venture outside park boundaries. Often, this exploration has led to raids on nearby farms for maize and grains as well as vegetables and fruits. Local people have responded by aggressively trying to protect their livelihoods, setting traps, hunting, or erecting barriers to their land. These residents have also come to mistrust protected-area staff, researchers, and tourists—endangering the cooperation of local communities in the park’s efforts to protect its wildlife.

Such “people-park conflicts” are not unique to Gombe National Park. In fact, conflicts between people and wildlife have increased substantially around protected areas during the past decade because of increasing human populations and their activities, including expanding settlements, agriculture, livestock husbandry, deforestation, charcoal burning, tourism, and research.3

For wildlife, the “edge effect” of human encroachment on habitat results in increased mortality and morbidity. The Gombe chimps have exhibited inter-community conflict—violence between two communities of chimpanzees that otherwise would not have come into contact with each other, but are now competing over the same area of forest. Stress has also become an issue, making the chimpanzees even more susceptible to conflict and disease.

To better understand how current conditions in Gombe will affect the chimpanzee population in the future, Mike Wilson, director of field research at the Gombe Stream Research Center, has overseen the Population and Habitat Viability Analysis, a computer-simulation exercise based on certain assumptions about chimpanzees’ fertility, mortality, and other variables. Results of the simulation show that, should present trends continue, Gombe’s chimpanzee population will continue to decline over the next 50 years, perhaps to about one-half of its current size.4

“Without adequate habitat, it will be impossible for the chimpanzee population of Gombe to increase or even to be maintained,” says Wilson.

Human-Animal Disease Transmission

While habitat loss is the biggest constraint to maintaining a viable population of chimpanzees in Gombe National Park, the biggest killer of the primates is disease, accounting for approximately one-half of chimpanzee mortality. Scientists believe that humans are likely the transmitters of many of the diseases—such as polio (with an outbreak in 1966); respiratory tract infections (outbreaks in 1968, 1978, 1987, 1996, 2000, and 2001-02), and scabies (in 1997)—that have manifested in the chimpanzee population over the past four decades.5

In Gombe, the most common ailment of chimpanzees is respiratory disease, including pneumonia. In 1996, at least 11 chimpanzees died from a flu-like epidemic, and in 2001 at least 30 fell ill after a similar outbreak.6 In both cases, researchers and park staff strongly suspect humans as the source of the virus.

The fact that humans share 97 percent or more of their genetic makeup with chimpanzees and other great apes means that the risk of disease transmission between humans and chimpanzees is potentially high. A study conducted in Kibale National Park, Uganda in 1999 suggests that chimpanzees there are indeed exposed to human diseases through their regular contact with both tourists and local residents.

Self-reported medical surveys were administered to tourists and to local community members to determine the potential for human-to-animal disease transmission. The returned tourist surveys indicated a high prevalence of disease symptoms, particularly diarrhea, as well as ongoing infectious diseases and a lack of current vaccinations. The local surveys also indicated a high prevalence of disease symptoms—in particular, respiratory disease.7

As in Kibale National Park, the close proximity of chimpanzees and humans in Gombe National Park increases the likelihood of disease transmission. Local residents, fishermen, tourists, researchers, and park staff regularly come into contact with the chimps, either intentionally or unintentionally.

“People and chimps often cross paths on the public-access beach that borders the park,” says Matatu Mushi, chief park warden in charge at Gombe National Park. “And chimps love to pick up litter that people leave behind there—they chew on clothing, cardboard, and any other human-made product. Unfortunately, this only increases the risk of disease transmission from humans to chimpanzees.”

While the risk to chimpanzees in Gombe is rising from human population growth and human activity around the park, protected areas do have tools at their disposal to guard animal populations—particularly great apes—from further deterioration. A PRB web article next month will detail some of these solutions and discuss how they could be applied to the chimpanzees of Gombe.



  1. The chimpanzees of Gombe National Park are not alone in experiencing dramatic population decline during the past several decades. All of the great apes subspecies—gorillas, chimpanzees, and orangutans—are considered “endangered.” Ape populations are declining in 96 percent of the protected areas where active research programs are being conducted, while apes outside protected areas have little hope for long-term survival. See “The Current Condition of Great Apes in the Natural Environment,” Pan Africa News 8, no. 1 (2001), accessed online at, on June 30, 2006.
  2. For Tanzania ‘s regional population distribution and growth rates (1967-2002), go to Tanzania Population and Development, accessed online at, on June 29, 2006. For the national growth rate of Tanzania, see Carl Haub, 2005 World Population Data Sheet (Washington, DC: Population Reference Bureau, 2005), accessed online at, on June 27, 2006.
  3. Titus Mlengeya and Vitalis Lyaruu, “Experiences with and the Challenges of Wildlife Health Management in the National Parks of Tanzania,” in Conservation and Development Interventions at the Wildlife/Livestock Interface: Implications for Wildlife, Livestock, and Human Health, ed. Steven A. Osofsky (Gland, Switzerland: IUCN, 2005).
  4. Interview with Michael Wilson on Feb. 7, 2006.
  5. Reference to the polio outbreak can be found in Jane Goodall, In the Shadow of Man (Boston: Houghton Mifflin, 1971). For respiratory disease outbreaks, see Mlengeya and Lyaruu, “Experiences with and the Challenges of Wildlife Health Management in the National Parks of Tanzania.” For a discussion of the scabies outbreak, see Anne Pusey, “Scabies in Chimpanzees of Gombe National Park, Tanzania,” European Association of Zoo and Wildlife Veterinarians Newsletter 1 (1998): 10.
  6. Interview with Shadrack Kamenya, director of conservation at Gombe Stream Research Center, Kigoma, Tanzania, on Feb. 4, 2006.
  7. Hayley Rebecca Adams et al., “Self-Reported Medical History Survey of Humans as a Measure of Health Risk to the Chimpanzees (Pan troglodytes schweinfurthii) of Kibale National Park, Uganda,” Oryx 35, no. 4 (2001): 308-12.

Environmental Security: PRB Talks With Thomas Homer-Dixon

(January 2001) PRB recently interviewed Dr. Thomas Homer-Dixon, director of the Peace and Conflict Studies Program at the University of Toronto. Dr. Homer-Dixon’s research is internationally-recognized for exploring the links among environmental scarcity, population, and civil violence in less developed countries. He is the author of Environment, Scarcity, and Violence (1999) and has co-edited (with Jessica Blitt) Ecoviolence: Links among Environment, Population, and Security (1998). He has also published numerous articles on the subject, including “Environmental Scarcities and Violent Conflict: Evidence from Cases,” in International Security (Summer 1994), and “The Ingenuity Gap: Can Poor Countries Adapt to Resource Scarcity?” in Population and Development Review (September 1995). His most recent book, The Ingenuity Gap, examines how societies cope with complex stress, including rapid environmental change.

With several colleagues, Dr. Homer-Dixon has developed a model of the relationship between the scarcity of renewable resources such as water and soil on the one hand, and the outbreak of violent conflict within countries on the other. In essence, the model describes how environmental scarcity contributes to certain destabilizing social effects that make violent conflict more likely.

PRB: What prompted you to make the connection between environmental scarcity and violent conflict the focus of your research for much of the 1990s?

Homer-Dixon: I had always been interested in environmental issues on the one hand, and conflict studies on the other, so I was naturally drawn to the overlap between these two areas. In addition, I was getting into this right after the fall of the Soviet Union, so there was room for thinking about new security issues. That’s not to say that the kind of conflict we’ve been looking at is new; it has actually been around for quite a while. Some of the case studies we’ve done have actually looked at conflicts — the “Soccer War” in El Salvador, for example — that predate the end of the Cold War.

PRB: Do you have a working definition of the term “environmental security?”

Homer-Dixon: No. I avoid that term because I think it is too open to misinterpretation. My research has focused on the relationship between environmental stress and specific kinds of violence — insurgencies, ethnic clashes, and rebellions in particular. Environmental stress we define in terms of the environmental scarcity that arises from ecological degradation, population growth, or skewed access to natural resources. But I have stayed away from trying to define “environmental security.” You can define security however you want, and I find that attempts to redefine or expand our concept of security often leave you with a term that is so broad that it is not very useful.

PRB: You’ve been involved in many different case studies looking at the ways in which scarcity of vital natural resources such as cropland can lead to violent conflict within countries. Where do you think the clearest connections between scarcity and violence have emerged?

Homer-Dixon: I think there are many cases that one could point to — I wouldn’t want to put one above the rest. It also depends on what kind of civil violence you’re talking about. If you’re talking about ethnic conflict, then one of the clearest cases is the massive movement of people out of Bangladesh into the Indian state of Assam in the 1970s and early 1980s that subsequently led to horrible violence in the 1980s. As for a more recent example, it has become clear that population pressures and land scarcity were aggravating factors behind the genocide in Rwanda in the mid-1990s. These are not isolated examples, though, and I don’t want to highlight one at the expense of the rest. They’re meant to demonstrate a broader trend. I could just as easily talk about how environmental scarcity has contributed to civil violence in Peru, the Philippines, Kenya, El Salvador, Pakistan, or many other countries.

PRB: Is the scarcity-conflict model that you have developed the only model that is out there for talking about how environmental issues and violent conflict are related?

Homer-Dixon: Gunther Baechler in Germany has done some interesting work as well. His work is not so different from ours, though — it’s mainly different approaches to categorizing things. Not many other people have really looked at this problem in a theoretical way. Of course, our model has been criticized by other social scientists, but the critics have not put forward a model of their own.

PRB: What does your model mean for policymakers? Where in the progression from environmental scarcity to violence are there opportunities for intervention?

Homer-Dixon: Every case is different, but there are a few general points to keep in mind. First, it’s best to intervene as early as possible. If you wait until conflict has broken out, the problem will have become too entrenched to resolve easily. The conflicts that arise from environmental scarcity tend to be chronic and diffuse, and this is exactly the kind of conflict that we have difficulty managing. These long-running conflicts can also erode the ability of governments to manage society, which of course exacerbates the situation.

Second, there is no one “magic bullet” that will fix these problems. The causes behind these conflicts are complex, and can include such problems as debilitating debt loads, social inequality, rapid population growth, and unsustainable agricultural practices. Policymakers thus need to respond with a broad and integrated set of responses at every level from international relations to the local community.

Third, governments do not have to launch capital-intensive programs to deal with these problems. Instead, officials can increase support for NGOs that are helping to rehabilitate environmental resources, or devote more resources to such activities as researching crops that can grow in eroded soil.

Fourth, many of the solutions that relieve environmental scarcity are worth implementing for other reasons. Such measures as debt relief and development of human capital are widely touted as important for promoting economic growth in impoverished communities around the world.

It’s also worth remembering that environmental scarcity never creates violence by itself; instead it interacts with what I call contextual factors, and some of these are subject to influence. For example, policymakers should try to make sure that prices accurately reflect the cost of resource use. Resource prices that are too low fail to generate the kind of innovation that can help relieve resource scarcity, and also promote overconsumption of the resource. Another key question is the extent to which the government is dominated by powerful elites that depend upon control of natural resources. If such elite groups are dominant and enjoy privileged access to vital resources, it’s very difficult to cope with environmental scarcity.

PRB: Do you think that governments and NGOs are getting better at taking advantage of insights from your model?

Homer-Dixon: There has definitely been interest in our work, particularly during the Clinton-Gore administration. A lot of our ideas have made inroads into the bureaucracy in Washington and also in NGOs. If in the early 1990s you had put forward the idea that environmental problems could be a destabilizing factor, people would have been in dismissive. I think that it has now actually become part of the received wisdom, and if you mention it people will say “I know about that — that’s nothing new.” Curiously enough, I think that’s a sign of success.


Stopping the Progression from Scarcity to Conflict

  • Intervene in the process as early as possible
  • Don’t look for one magic bullet fix — solutions must be multi-faceted
  • Solutions don’t have to be capital-intensive
  • Many potential solutions are worth implementing for other reasons

For More Information

For detailed case studies of environmentally-related conflicts, visit the website of the Project on Environment, Population, and Security at the University of Toronto:

For the latest on Professor Homer-Dixon’s research, visit his personal web page:

For updates on developments in the field of environmental security, visit the Environmental Change and Security Project at the Woodrow Wilson International Center for Scholars:

For more on Professor Homer-Dixon’s research, read PRB’s article “Environmental Scarcity and the Outbreak of Conflict.”

Bingham Kennedy, Jr. is associate editor at the Population Reference Bureau.


Population and Climate Change

(November 2000) International negotiations aimed at ameliorating climate change have generally focused on consumption patterns in industrialized countries rather than global population growth. Industrialized countries have produced the bulk of greenhouse gas emissions to date: The United States alone accounted for 23 percent of total world CO2 emissions in 1996, according to the U.S. Department of Energy’s Carbon Dioxide Information Analysis Center (CDIAC). The staggering levels of emissions in more developed countries stem mainly from consumption patterns that lead to high per capita emissions (see Figure 1). In 1996, U.S. per capita emissions of carbon dioxide stood at 20.0 metric tons, while for Germany and Japan the figures were 10.5 and 9.3 metric tons, respectively. In contrast, the global average for that year was 4.0 metric tons per capita. For sub-Saharan Africa, it was 0.8 metric tons.

Figure 1
Per Capita Carbon Dioxide Emissions, Top Ten Countries, 1996 (metric tons)

Source: U.S. Department of Energy, Carbon Dioxide Information Analysis Center, published in the World Bank’s World Development Indicators 2000.

The developing world is fast becoming a substantial contributor to climate change, however. With economies and populations in less developed countries growing considerably, so are their levels of greenhouse gas emissions. In China, emissions of carbon dioxide rose from 1.5 to 2.8 metric tons per capita between 1980 and 1996, while the population increased from 984 million to 1.22 billion. As a result, China accounted for 15 percent of the world’s total emissions in 1996, second only to the United States (see Figure 2). Less developed countries altogether accounted for 23 percent of worldwide emissions in 1996, as opposed to under 17 percent in 1980.

In the long run, efforts to curb climate change will have to address both consumption patterns that contribute to high per capita emissions as well as the growing number of consumers worldwide. To involve less developed countries in the solution, future climate change agreements are likely reflect the view that people of the world enjoy equal rights to use the atmosphere to dispose of the carbon generated by fossil fuel combustion. If adopted, such a principle would make the overall size of the human population a critical variable. The larger the population becomes, the lower the average per capita level of emissions commensurate with acceptable levels of greenhouse gas production. In other words, as population grows, each individual’s right to pollute shrinks.

Figure 2
Total Carbon Dioxide Emissions: Top Ten Countries, 1996 (million metric tons)

Source: U.S. Department of Energy, Carbon Dioxide Information Analysis Center, published in the World Bank’s World Development Indicators 2000.

Population growth also increases the number of people who will be affected by climate change, though it remains unclear how specific communities will be affected. In addition to rising temperatures and changing weather patterns, a number of less obvious effects could occur. Agricultural productivity might be boosted in some areas, but disrupted in others, worsening malnutrition. Global warming could also lead to a redistribution of disease-carrying insects, introducing unaccustomed human populations to such diseases as malaria, dengue fever, yellow fever, and encephalitis.

The Intergovernmental Panel on Climate Change has identified Africa as the continent that is most vulnerable to the impacts of the projected changes because widespread poverty limits adaptation capabilities. But other regions will be affected as well. Countries with large coastal populations — China, India, and the United States, for example — may have to contend with extensive damage from rising sea levels. In countries that are susceptible to flooding such as Bangladesh, more severe storms and changing rainfall patterns could exacerbate existing problems, endangering communities that already live on vulnerable land. In the end, there will no doubt be additional, unanticipated effects: The full range of climate change’s impact remains to be seen.

Bingham Kennedy, Jr. is an associate editor at the Population Reference Bureau.