An Overview of Apes in Africa

All the great apes, except the orang-utan, live in tropical Africa. They comprise two species of chimpanzee, the robust chimpanzee (also known as the common chimpanzee) and the gracile chimpanzee (also known as the bonobo or pygmy chimpanzee), and two species of gorilla, the western gorilla and the eastern gorilla. All four of Africa's great apes are found near the equator, primarily inhabiting tropical forest where they are essential components of the richest assemblage of species on the continent. Unfortunately, apes are also a source of food and cash for many people in West and Central Africa. Hunting, together with loss of habitat, has greatly reduced both the distribution and the abundance of all four species.

Chimpanzees

The robust chimpanzee lives in savanna woodlands, grassland-forest mosaic and tropical moist forest, and is found from sea level to an elevation of about 3,000 m. This species probably once spanned most of equatorial Africa from southern Senegal to southwestern Tanzania, ranging over all or part of at least 23 countries. Today, the robust chimpanzee is the most widely distributed of Africa's apes, occurring in 21 or 22 countries between 13° N and 7° S.
There are four subspecies of robust chimpanzee. The western chimpanzee once ranged over ten to twelve countries, but now an estimated 40,000 members of this subspecies are patchily distributed in eight or nine countries from southeastern Senegal eastwards, possibly to the Niger River in Nigeria. Recent genetic research supports the recognition of the robust chimpanzee in eastern Nigeria and western Cameroon as a distinct subspecies, the Nigeria chimpanzee. Its range covers what was formerly considered the southern range of the western chimpanzee and the northern range of the central chimpanzee. A reasonable "guess" is that there are today 4,000–6,000 Nigeria chimpanzees and that their geographic range is approximately 20,000 km².
The range of the central chimpanzee is very much larger, covering approximately 270,000 km² across seven countries in the region between the Sanaga, Ubangi and Congo rivers. Probably between 47,000 and 78,000 individuals inhabit this region.
The eastern chimpanzee, with a population estimated at between 75,000 and 118,000, is the most numerous of the chimpanzee subspecies. Its range is also the largest, covering about 500,000 km² and spanning seven countries from the Ubangi River in the central Democratic Republic of the Congo, north of the Congo River to southwestern Sudan and south to southwestern Tanzania.
The gracile chimpanzee is endemic to the grassland-forest mosaic, lowland forest and swamp forest of the central Congo Basin south of the Congo River in the Democratic Republic of the Congo. It lives within a range of elevation of 300-500 m, and numbers between about 30,000 and 50,000 individuals.

Gorillas

Gorillas occur in two distinct regions, western Central Africa and eastern Central Africa, which are separated by about 900 km of forest in the Congo Basin. Recent studies show that the genetic differences between the gorillas in the eastern and the western region are slightly greater than those between the robust chimpanzees and the gracile chimpanzee. This genetic distance, together with morphological, ecological and behavioural differences, provide support for recognizing two species, the western gorilla and the eastern gorilla.
The western gorilla inhabits lowland forest, swamp forest and submontane forest from sea level to about 1,600 m. Two subspecies are recognized: the western lowland gorilla and the Cross River gorilla. The former is distributed over six countries from south Cameroon to Angola's Cabinda enclave, covering an area of roughly 445,000 km². As in the cases of the chimpanzees, however, the actual range that gorillas occupy is much less than the geographic range, as there are large areas in which no gorillas are present.
The Cross River gorilla, a recently resurrected subspecies, inhabits lowland and submontane forest in the upper Cross River region on the Nigeria-Cameroon border, about 260 km north of the range of the western lowland gorilla. With only about 200-250 individuals remaining, this is the most threatened of the gorilla subspecies.
The eastern gorilla lives in submontane and montane forest at an altitude of between about 800 and 4,000 m. There are two currently recognized subspecies: the mountain gorilla and Grauer's gorilla. The mountain gorilla is restricted to one population of about 300 individuals. This population lives in a 375 km² area in the Virunga Volcanoes where the borders of Uganda, Rwanda and the Democratic Republic of the Congo meet.
The taxonomic status of the 300 or so gorillas that range over an area of about 215 km in the Bwindi Forest in southwestern Uganda is highly uncertain. Although they have been called "mountain gorillas", differences between them and the gorillas of the Virungas sugest that the "Bwindi gorilla" represents a third subspecies or that they are Grauer's gorillas.
Grauer's gorilla has a discontinuous distribution in eastern Democratic Republic of the Congo from Lake Edward south to Lake Tanganyika. This subspecies numbers roughly 17,000 animals and has a geographic range of about 15,000 km².

Conservation Status

At an international workshop held in Orlando, Florida, in March 2000, members of the IUCN/SSC Primate Specialist Group and other senior scientists met to reassess the taxonomy and degree of threat status of the world's primates in preparation for the publication of the next Red Data Book. The participants concluded that, in the light of the recent and continuing rapid declines in the numbers and distributions of Africa's apes, all four species and 6 of the 8 subspecies are "Endangered". Two subspecies, the mountain gorilla and the Cross River gorilla, are "Critically Endangered", as is the population of gorillas in the Bwindi Impenetrable Forest. Clearly conservation efforts must focus on these taxa.

Threats

What are the current threats to populations of apes in Africa? On a continent where food production per person is on the decline, where one person in three is malnourished, and where the human population is expected to double by the year 2025, the requirements for food, clothing, fuelwood and shelter will continue to grow rapidly. This is coupled with a growing demand for Africa's natural resources by people in Europe, Asia and North America. As a result of this exploitation, the populations of chimpanzees and gorillas are being reduced, fragmented and destroyed, both indirectly through habitat degradation and loss, and directly through unsustainable hunting.
Throughout their ranges, chimpanzees and gorillas are officially protected under both national and international law. Nonetheless, during the last decade the commercial (i.e., non-traditional, non-subsistence) hunting of apes has increased greatly as logging companies open up large tracts of previously inaccessible forest. Hunters have completely destroyed populations of apes and greatly reduced many others. As a result, today there are large tracts of suitable habitat where chimpanzees and gorillas are either at low densities or no longer present. Hunting, rather than the loss of forest habitat, is now probably the most significant and immediate threat facing all of Africa's apes, as well as many other species of primates and other large mammals.
The increase in hunting not only threatens populations and taxa of apes, but it also brings people and apes into closer and more frequent contact than ever, with the consequence that the rate of disease transmission between humans and apes has increased. Medical researchers now recognize links between the "opening up" of the tropical forest by logging firms, the increased hunting of great apes and the more frequent transmissions of diseases between apes and humans. For example, the virus that gave rise to HIV-1 in humans may have been transmitted through blood contact during the butchering of robust chimpanzees for food.
Disease can be a major problem in efforts to conserve endangered populations and taxa. Exotic strains of pathogens have the potential to become hyperdiseases by "jumping" to hosts not previously exposed to the strain. Experience tells us that this can result in 80-100% mortality, with even large populations being virtually destroyed by disease. Yet disease as a threat to free-living apes remains a neglected topic. Since chimpanzees and gorillas are phylogenetically close to man, they are highly susceptible to numerous human infectious diseases, especially viruses. The risks and consequences of disease transmission between humans and apes are predicted to become more serious as once-stable ecosystems and large (genetically diverse) populations of apes are fragmented and reduced.
Several small, critically endangered populations of apes are being exposed to contact that is both frequent and close (i.e., less than 1 m or touching) with large numbers of people. In eastern Central Africa, all five of the gorilla tourism programmes are based on populations of only 240-340 individuals, while all seven of the chimpanzee tourism programmes are based on populations of 20-650 individuals.
The single population of 300 mountain gorillas in the Virunga Volcanoes is particularly badly affected. When the security situation allows, 70% of the gorillas in this population - and therefore of this subspecies - is visited daily by more than 70 tourists and a similar number of guides, porters, rangers and researchers. There have been several outbreaks of disease which can probably be attributed to humans, including an epidemic in 1988 in which 6 habituated gorillas died of respiratory illness and 27 more became ill and were given injections of penicilline. It appeared that the measles virus or a related morbillivirus was responsible. As a result, 65 gorillas in seven habituated groups were vaccinated against human measles. No further signs of respiratory disease were seen after the initiation of the vaccination campaign. There is no evidence that this disease affected gorillas in the unhabituated groups. In 1990, broncho-pneumonia affected 26 of 35 gorillas in a group visited by tourists and four of the gorillas died.
Similar episodes have occurred among other great ape populations. There were at least 6 epidemics in the research and tourist community of robust chimpanzees at Gombe National Park, Tanzania, between 1966 and 1997. The diseases involved include poliomyelitis, pneumonia and scabies. In the course of the epidemics at least 42 chimpanzees either were crippled or died. During the 1980s there were about 150 chimpanzees in Gombe National Park. Today there are fewer than 100.
In 1993/1994, at least 11 habituated robust chimpanzees (perhaps as many as 18) died in the Mahale Mountains, Tanzania, from a "flu"-like illness. It is suspected that tourists or other people in contact with these chimpanzees transmitted the virus. In 1992 and 1994, outbreaks of Ebola or a similar disease killed at least 20 of the 40 or so robust chimpanzees in the research community in Tai Forest, Côte d'Ivoire. The number of adult males in this community was reduced from eight to two. One student fell seriously ill (but recovered) from the same virus after participating in an autopsy. It is probable that the disease resulting in at least some, perhaps all, of these epidemics were transmitted to the apes by people.

Conclusions

There is broad consensus among field workers that chimpanzee and gorilla numbers are in sharp decline in the wild, that the rate of decline is rapidly accelerating, and that all four species will become extinct in the wild if the causal factors are not sufficiently addressed. The population estimates for the apes are small in the context of species survival potential, and particularly so in view of the extreme fragmentation of their populations and habitats. It is obvious that further exploitation of these species, and of their habitats, should not be permitted, and that more effective conservation measures need to be implemented.
To date, all that can be claimed is that we have pushed forward somewhat the time when Africa will begin to lose some of its taxa of great apes. The present decline in numbers will not be reversed without more work, more ideas, more approaches, more money and, above all, more people who are willing to commit to an active role. This problem must be made an issue of global concern if all taxa of African apes are to have a long-term future in the wild. We must all find a way to help make the "African great ape crisis" a global issue and a focus of effective global action.

Tom Butynski

Dr. Thomas Butynski has conducted wildlife research in Africa since 1971. From 1978 to 1993 he studied primates and worked on rain forest conservation in Uganda. Now he works for Conservation International and in addition for the IUCN/SSC Primate Specialist Group. Since 1995 he has made surveys in endangered montane forests in eastern Zaire/Democratic Republic of the Congo.

Current Numbers and Geographic Ranges of Africa's Great Apes

Gorillas in general - overview

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