What, if Anything, Is Taxonomy?
Gorilla Journal - December 2000
Taxonomy and classification, two words that have come to mean much the same thing, are "the ordering of organisms into groups, on the basis of their relationships" (modified after Simpson, 1961).
It is important to realize that taxonomy is a part of biological science, like ecology, behaviour, physiology or evolution. So a classification is a scientific hypothesis, subject to modification if new evidence comes to light, or if new understandings are brought to bear. In this sense, a classification is never finalized, there is no "official taxonomy". There can only be a statement of the present position, as seen by a particular taxonomist, taking (one hopes) all relevant information into account.
Nowadays, nearly all taxonomists agree that common ancestry is the most objective criterion for orders, families and genera (and suborders, subfamilies and so on); so, the lemurs, tarsiers, monkeys, apes and humans are classified in the order Primates because they share a common ancestor not shared by other mammals. In older books, humans are usually classified alone in the family Hominidae, whereas orangutans, gorillas and chimpanzees are placed in a different family, Pongidae; but it is now clear that humans, chimpanzees and gorillas share a common ancestor not shared by the orangutan, so we should classify them together in a group that excludes the orangutan. As all four are rather closely related, it is now almost universal to place them in a single family, for which the correct name is Hominidae, with two subfamilies: Ponginae for Pongo (the orangutan) alone, and Homininae combining Homo (humans), Pan (chimpanzees) and Gorilla (gorillas).
I referred to "the correct name" because, unlike taxonomy, nomenclature is objective. Once one has decided what the most appropriate taxonomy is, the question of what names to call the resulting taxonomic groups is decided by the rules of naming, laid down in the International Code of Zoological Nomenclature. In the main, one must use the earliest available name given to a species (or subspecies, or a genus, or a family).
A species name is a binomial. The first word is the generic name, the second is the specific name. So in the genus Macaca we have the species Macaca mulatta, Macaca fuscata and others. In the genus Pan we have Pan troglodytes (common chimpanzee) and Pan paniscus (pygmy chimpanzee or bonobo). Always begin the generic name with a capital letter; always begin the specific name with a small letter.
What Are Species?
The category "species" needs to be discussed separately, for reasons that will become clear. The great taxonomist Ernst Mayr defined a species as being "reproductively isolated"; his fullest discussion of what this would mean was published nearly 40 years ago (Mayr, 1963), but is still well worth reading. The concept of reproductive isolation has been much misunderstood. It actually means that two species do not, "under natural conditions" (meaning, more or less, in the wild) interbreed with each other. What it does not mean is that they do not interbreed with each under any circumstances. Thus, horses and mules interbreed, though their hybrids (mules and hinnies) are almost invariably sterile; and lions and tigers can be persuaded to interbreed in zoos, and their hybrids are fertile yet nobody, as far as I know, has ever suggested that they should be included in one species. This is known as the Biological Species Concept (BSC).
But what if two animal populations live in different geographic areas (are allopatric), so do not have the opportunity to interbreed? Consider the following three levels of separation:
Japanese macaques (on all the Japanese islands) differ strongly and consistently from rhesus macaques, which live on the Asian mainland. Japanese and rhesus macaques are customarily separated into different species, Macaca fuscata and Macaca mulatta respectively.
Within Japan, the macaques of Yakushima (=Yaku island) differ on average from those of the three main islands, but not absolutely. The Japanese macaques are customarily divided into two subspecies, Macaca fuscata fuscata (large islands) and Macaca fuscata yakui (Yakushima).
Macaques on the three main Japanese islands of Honshu, Shikoku and Kyushu are indistinguishable morphologically from each other. Macaques of all three islands are regarded as belonging to one and the same subspecies, Macaca fuscata fuscata.
Could the essence of species, then, be that they are morphologically distinct, and if so, how much difference is required?
It is today possible to examine DNA sequences directly, and these, like morphological characters, may differ between two populations. Those sequences that have been analysed tend either to code for enzymes (haemoglobin, cytochrome oxidase) or not to code for anything (pseudogenes, introns) and so apparently are "silent". No sequences that code for morphological characters have yet been identified, let alone analysed, though clearly they exist, because such morphological (visible or metrical) differences as occur between individuals, and hence between populations, are, to a greater or lesser degree, heritable. So morphological differences are a special case of genetic differences. Let us then rephrase the question: Could the essence of species be that they are genetically distinct, and if so, how much difference is required?
The view promoted by the ornithologist Joel Cracraft nearly twenty years ago (Cracraft, 1983), and now widely adopted, is that species should be "diagnosable", or 100% distinct; that is to say, that every member of a species should be distinguishable from every member of all other species. This is known as the Phylogenetic Species Concept (PSC). Some of the DNA sequences of pseudogenes could likewise be identified infallibly though, interestingly, in their mitochondrial DNA some rhesus macaques are much more similar to Japanese macaques than to other Rhesus so not all genes give the same results.
In the Japanese vs. Rhesus macaque example, there is not the slightest possibility of determining whether they are separate species or not using the BSC. (These drawbacks apply, quite frankly, to most comparisons between pairs of populations.) But the PSC can be applied, and we find that the two are genetically distinct: there are some genes which are universal (fixed) in the one, absent from the other. Each can be diagnosed. By contrast, Yakushima and larger-island macaques differ on average only: no gene (including morphological character) has been discovered which is universal in the one, absent in the other.
Although species theory is very controversial, there is a growing consensus that the BSC has outlived its usefulness as a criterion. It is still a touchstone, in that it illustrates in some important way what a species is all about, but it is simply inapplicable in most cases. The PSC, however, always offers objective criteria, and it is likely that a majority of taxonomists now adopt some version of it, consciously or subconsciously.
A species, then, is a population (or group of populations) which differs diagnostically (i.e. absolutely) from others. Put another way, it has fixed genetic differences from others. Put another way, there are gaps between different species. Below the species level, relationships between populations are reticulate (shared genes, shared characters). In cladistic jargon, the species is the terminal on the cladogram.
What Are Subspecies?
Subspecies are geographic segments of a species. They are populations which differ from one another as a whole, but not absolutely. In this case it is relevant to ask how much they should differ to merit being called different subspecies what proportion of individuals should be recognizable? The decision is somewhat arbitrary, but a good rule of thumb is the "seventy-five percent rule" (Mayr, 1963): three-quarters of individuals in a population should differ from all individuals in other populations of the species.
Subspecific names are trinomials. The first two words denote the species; the third denotes the subspecies itself. Note that there is never just one subspecies, there are none or there are two or more: a species is divided into subspecies. As mentioned, Macaca fuscata is divided into two subspecies. One, the mainland Japanese macaque, is called the nominotypical subspecies, and it subspecific name repeats the specific name: Macaca fuscata fuscata. It is the one that occurs at the type locality (the locality from which the species was first described). The other has its own subspecific name, peculiar to it: Macaca fuscata yakui.
Applying the Criteria to Gorillas
Gorillas are found in two widely separate parts of Africa. Western gorillas live in the West-Central African region: southwestern Central African Republic, Congo, Mayombe, Luanda, Gabon, Río Muni, southern Cameroon, southeastern Nigeria, and the Djabbir region of the Democratic Republic of Congo. Eastern gorillas live in the East-Central African region: eastern D.R. Congo, southwestern Uganda, northern Rwanda. Eastern and Western gorillas are somewhat different. How to classify them?
In my experience, every gorilla is at once distinguishable as an Eastern or a Western gorilla. They are diagnosable. They differ 100% in their external characters, and in the skull and teeth. Their mitochondrial DNA (mtDNA) sequences are absolutely different; note that what is important, in deciding whether they are different species or not, is not the fact that their sequence differences show that they diverged over a million years ago (Garner & Ryder, 1996), but that they have fixed genetic differences between them. Even if we knew nothing of their mtDNA, we would still be justified in concluding that they have fixed genetic differences, because their morphological differences are absolute, and are heritable. So, under the PSC, they rate as distinct species.
Note that, because their distributions are entirely separate, we have not a hope of applying the BSC to them just as in the rhesus and Japanese macaque example. Unless we apply the PSC, we will have no objective means of deciding whether to call them different species or not. Some biologists do not accept the PSC; but for myself, I do not see how else we are to arrive at anything like a repeatable, falsifiable hypothesis for their classification.
The first gorillas to be described were from the Gabon estuary and were Western gorillas. The Reverend Savage, who first made gorillas known to science (Savage & Wyman, 1847), gave the name Troglodytes gorilla.
About the generic name: The name then in common use for the chimpanzee was Troglodytes niger, which had been given to it by the great French zoologist, Etienne Geoffroy St. Hilaire, in 1812; Savage thought that the gorilla was a giant species of chimpanzee, which is why he called it Troglodytes gorilla. But the chimpanzees generic name had to be changed, because the same name, Troglodytes, had earlier been applied (by Vieillot in 1806) to the wren! So the next available name, Pan Oken, 1816, is now used for the chimpanzee. But the gorilla is in any case no longer considered to belong to the same genus as the chimpanzee, and in fact as early as 1852 Isidore Geoffroy St. Hilaire, son of Etienne, gave it its own generic name, Gorilla. And that is why the correct scientific name for the Western gorilla is Gorilla gorilla.
In 1902, Captain Oskar von Beringe discovered the Eastern gorilla (he "discovered" it by shooting one), and it was described the following year (Matschie, 1903), and named after him: Gorilla beringei. Von Beringes gorilla was from Mt. Sabinyo in the Virunga Volcanoes, so this is the type locality of G. beringei. I have argued, above, that Eastern and Western gorillas are distinct species, so both Savages and Matschies names are valid.
Paul Matschie, describer of Gorilla beringei, was by modern standards a great "splitter" of species: where we today see a single species, he saw two, three or more. Between 1905 and 1914 he described several more supposed new species of gorilla from different regions of Cameroon: Gorilla diehli, jacobi, schwarzi, hansmeyeri and zenkeri (and the Hon. Walter Rothschild even named one after him: Gorilla matschiei!). In 1914, too, he described a supposed new species, Gorilla graueri, from the Itombwe Mountains, in the D.R. Congo west of Lake Tanganyika. Other people described supposedly new subspecies of Gorilla gorilla: G. g. halli from Río Muni, G. g. uellensis from Djabbir, and G. g. rex-pygmaeorum from Mt. Tshiaberimu.
Two of Matschies "species" do actually denote different subspecies. It does not matter that he described them as species; we can also use the names for the subspecies they really are.
(1) The so-called Eastern Lowland gorilla, from the Itombwe Mountains, Kahuzi-Biega, Mt. Tshiaberimu and the D.R. Congo lowlands east of the Lualaba, is different from the true Mountain gorilla of the Virunga Volcanoes; but the morphological characters overlap slightly, and although there is no difficulty in distinguishing the two as a whole, I do not believe that every single individual could be allocated to one or the other. So I do not think that they are different species; instead, I class them as subspecies of Gorilla beringei. Because the Eastern Lowland gorilla occurs in the Itombwe Mountains, type locality of Matschies G. graueri, its correct name is Gorilla beringei graueri. (In the days when I assumed that all gorillas belong to one single species, I called it Gorilla gorilla graueri; but, as explained above, I now conclude that all Eastern gorillas belong together in a species different from Western). The name rex-pygmaeorum, given to Mt. Tshiaberimu gorillas, denotes the same subspecies, so is a synonym of graueri; but if, at some future time, someone considers that Mt. Tshiaberimu gorillas are a different subspecies from Itombwe gorillas, the name will have to be resurrected. The true Mountain gorilla is Gorilla beringei beringei.
(2) It has recently been argued (Stumpf et al., 1998; Esteban Sarmiento, in preparation) that the gorillas of the Cross River district, on the NigeriaCameroon border, are somewhat different from other Western gorillas, and should be regarded as a separate subspecies. Matschies name diehli was given to gorillas from this region. The Cross River gorilla must therefore be known as Gorilla gorilla diehli, and other Western gorillas will be Gorilla gorilla gorilla.
I should add that long ago I studied and measured the three skulls on which the name uellensis was based and, unexpectedly (because the population is geographically so isolated), I could find no differences at all from any other Western gorillas. So I conclude that they are probably examples of Gorilla gorilla gorilla.
Sarmiento et al. (1996) consider that the gorillas of the Bwindi-Impenetrable Forest are different from all other Eastern gorillas, whether Mountain (Virunga) or Eastern Lowland. Should further specimens support this hypothesis, then a new subspecies of G. beringei will have to be described and named because curiously, despite the arrant splitting that went on in the early 20th century, no-one ever got around to looking at any Bwindi gorillas!
Cracraft, J. 1983. Species concepts and speciation analysis. Current Ornithology (R.F. Johnston, ed.), 1:159-187. New York: Plenum Press.
Garner, K.J. & O.A. Ryder. 1996. Mitochondrial DNA diversity in gorillas. Molecular phylogenetics and evolution, 6:39-48.
Matschie, P. 1903. Über einen Gorilla aus Deutsch-Ostafrika. Sitzungsberichte der Gesellschaft naturforschender Freunde, Berlin, 1903:253-259.
Mayr, E. 1963. Animal Species and Evolution. Oxford University Press.
Sarmiento, E.E., T.M. Butynski & J. Kalina. 1996. Gorillas of Bwindi-Impenetrable Forest and the Virunga Volcanoes: taxonomic implications of morphological and ecological differences. American Journal of Primatology, 40:1-21.
Savage, T.S. and J. Wyman, 1847. Notice of the external characters and habits of Troglodytes gorilla, a new species of orang from the Gaboon River; Osteology of the same. Boston Journal of Natural History, 5:417-442.
Simpson, G.G. 1961. Principles of Animal Taxonomy. Oxford University Press.
Stumpf, R.M., J.G. Fleagle, W.L. Jungers, J.F. Oates & C.P. Groves. 1998. Morphological distinctiveness of Nigerian gorilla crania. AAPA Abstracts, 1998:213.
An Overview of Apes in
Gorilla Journal - December 2000
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.
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 4,0006,000 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 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 Congo. It lives within a range of elevation of 300500 m, and numbers between about 30,000 and 50,000 individuals.
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 NigeriaCameroon border, about 260 km north of the range of the western lowland gorilla. With only about 200250 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 Congo meet.
The taxonomic status of the 300 or so gorillas that range over an area of about 215 km2 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 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.
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 six of the eight 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.
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 80100% 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 240340 individuals, while all seven of the chimpanzee tourism programmes are based on populations of 20650 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 six 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 six 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.
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.
A longer version of this article was originally published in Africa Environment & Wildlife, Vol. 8, No. 5 (June 2000).
Butynski, T.M., in press. Africa's Great Apes. In Apes and Humans at an Ethical Frontier. B.B. Beck et al., eds. Washington, D.C.: Smithsonian Institution Press.
Butynski, T.M. & J. Kalina, 1998. Gorilla tourism. Pp. 280300 in Conservation of Biological Resources. E.J. Milner-Gulland and R. Mace, eds. Oxford: Blackwell.
Current Numbers and Geographic Ranges of Africa's Great Apes
|Robust chimpanzee (Pan troglodytes)||200,000||838,000|
|Western chimpanzee (P. t. verus)||40,000||48,000|
|Nigeria chimpanzee (P. t. vellerosus)||5,000||20,000|
|Central chimpanzee (P. t. troglodytes)||62,000||270,000|
|Eastern chimpanzee (P. t. schweinfurthii)||96,000||500,000|
|Gracile chimpanzee (Pan paniscus)||40,000||120,000|
|Western gorilla (Gorilla gorilla)||94,000||445,000|
|Western lowland gorilla (G. g. gorilla)||94,000||445,000|
|Cross River gorilla (G. g. diehli)||200||300|
|Eastern gorilla (Gorilla beringei)||17,000||15,000|
|Mountain gorilla (G. b. beringei)||300||400|
|Grauer's gorilla (G. b. graueri)||17,000||15,000|
|Bwindi gorilla (G. b. subspecies?)||300||200|
Gorilla Journal - December 2000
The bushmeat crisis, the commercial, illegal trade in meat from wild animals, which is particularly common in West and Central Africa, has been the theme of various activities this year. The exhibition Gorillas in the Cooking Pot in the Stuttgart Zoo from June to September had a great response. In particular, Marianne Holtkötter supported the exhibition in every conceivable way. We also have to thank Professor Jauch, the Director of Stuttgart Zoo, for his courage and trust and for the funding, all of which made the exhibition possible in the first place.
Shortly after the exhibition had been opened, German zoo directors and EEP coordinators had a meeting in Stuttgart and they seized the opportunity to have a look at the 34 posters on the bushmeat problem. There was great interest in taking the exhibition to other zoos. Consequently, it went to Cologne Zoo in October and will stay there until December.
From January to March 2001 it can be seen in Neunkirchen Zoo, from April to May 2001 in Heidelberg Zoo and from June in Karlsruhe. Besides, the zoos of Krefeld, Zürich, Herberstein, Basel and Hamburg will also show the exhibition. In exchange, the zoos will donate a certain amount of money to the Berggorilla & Regenwald Direkthilfe. As other organisations (Rettet den Regenwald, Wild Chimpanzee Foundation, Bonobo In Situ Project, Save the Drill, World Society for the Protection of Animals) also contributed material, they will help to determine which projects working against the bushmeat trade will receive the money.
The exhibition formed the basis of a European-wide bushmeat campaign initiated by the European Association of Zoos and Aquaria (EAZA). The campaign is to inform the visitors to European zoos about the background of the bushmeat trade and collect donations for organisations working to find a solution to the bushmeat problem. The Berggorilla & Regenwald Direkthilfe is one of them.
In addition, signatures are collected for a petition calling upon the political decision-makers in Europe and Africa to initiate effective measures to solve the bushmeat problem. The petition was laid out publicly for the first time during the exhibition in Stuttgart. We collected 20,000 signatures there. The aim is to get at least one million signatures. When this is achieved, the petition will be handed over to the leaders of African nations by Jane Goodall and others. This campaign will probably run until October 2001 and hopefully receive a lot of attention from the media.
In the USA, local organisations are also very active. Working groups spring up everywhere, because people now recognize the severe threat the bushmeat trade is posing. This happened during the spring 2000 CITES conference, for instance. During the World Conservation Congress in Amman, the IUCN passed a resolution to ban the illegal bushmeat trade. It is encouraging to see that organisations and institutions worldwide seem to cooperate well in this campaign.
In 1929 Harold Coolidge revised the genus Gorilla to comprise a single species, despite clear differences in morphology between the western and eastern populations. Today the single-species classification is still the most widely used, although increasingly researchers are advocating a two-species taxonomy, with the West African gorillas belonging to Gorilla gorilla (with the subspecies Gorilla gorilla gorilla and Gorilla gorilla diehli) and the eastern gorillas to Gorilla beringei (with subspecies Gorilla beringei beringei and Gorilla beringei graueri).
The most widely stated criterion for species-level separation of two populations is whether or not they interbreed. However, since western and eastern gorillas never meet in the wild, we must rely on other methods. One way is to compare the amount of difference between two populations relative to that seen in other closely related species, in an effort to achieve consistency within a larger taxonomic group. For gorillas, this most commonly means comparing the amount of difference between western and eastern gorillas relative to that between common chimpanzees (Pan troglodytes) and pygmy chimpanzees, or bonobos (Pan paniscus).
Genetic Distance Studies
Some of the recent discussion of revising gorilla taxonomy has been motivated by results from studies examining the amount of genetic distance between gorilla populations. Maryellen Ruvolo and co-workers sequenced a portion of mitochondrial DNA (mtDNA) and found that the difference between eastern and western gorillas was about the same as that seen between common chimpanzees and bonobos. Since chimps and bonobos are considered different species, it was suggested that perhaps we should recognize two species of gorillas. Likewise, Karen Garner and Oliver Ryder found the same picture when they sequenced a different part of mtDNA.
Recently, Michael Jensen-Seaman and Ken Kidd examined yet another region of mtDNA in western and eastern gorillas. They found very similar results as had previous studies of mtDNA. That is, that the amount of difference between eastern and western gorillas was about as large as that seen between chimpanzees and bonobos. This suggests that western and eastern gorillas have been reproductively isolated for perhaps as long as 2 or 3 million years.
However, these same researchers also examined DNA sequence variation in the nuclear genome of these same gorillas and chimpanzees, but found somewhat different results. Specifically, they found that the eastern and western gorillas were not nearly as different from each other as were chimps and bonobos. This pattern was consistent across multiple nuclear genetic loci, and suggests that perhaps western and eastern gorillas have been in reproductive contact much more recently than have chimps and bonobos.
It is difficult to explain the discrepancy between the mtDNA and the nuclear DNA findings. In general, we expect the differences between the two genomes to be roughly similar, except for species in which females do not transfer from their natal group. Since female gorillas do transfer, the different patterns observed cannot be due to any simple sex-biased dispersal pattern.
Implications for Biogeography and Taxonomy
If eastern and western gorillas have experienced much more recent gene flow than have chimpanzees and bonobos, then either the initial split between these gorillas occurred more recently than the chimp/bonobo split, or there has been periodic gene flow between western and eastern gorillas during the last 2 million years or so.
Periodically during the last million years, Africa was warmer and wetter than today. During these times, the extent of the tropical forest would have been greater than at present, providing a possible corridor for migration between western and eastern gorillas north of the Congo River/Ubangi River. Along these lines, it is tempting to speculate that the population of gorillas which might have existed near Bondo in northern Democratic Republic of Congo in the earlier part of the 20th century may reflect a relict population from these intermittent forest connections. In contrast, after bonobos were split off from chimpanzees by the Congo River, there would seemingly be no possibility of gene flow between what are now the two species of Pan.
Others have made the argument that since chimpanzees and bonobos are definitely considered separate species, and since western and eastern gorillas initially appeared to be as genetically different as chimps and bonobos, then we should divide gorillas into two species. If we now believe that western and eastern gorillas may not be as different as we thought, does that mean that we should not separate western and eastern gorillas into separate species? No. Taxonomy is more complex than sequencing a little bit of DNA. There is no objective standard of how much genetic difference, or how much time since separation, is required to consider two populations different species. The use of the "chimp-bonobo" standard may provide some comparative measure of divergence, but there is no reason to believe that the separation between chimps and bonobos represents any sort of minimum level of divergence required for species level status. The relationship between genetic distance and reproductive isolation is not at all understood.
Given the discrepancy between the results observed from the mitochondrial genome and those from the nuclear genome, more data are clearly needed to resolve the issue of exactly how genetically different are western and eastern gorillas. Once this rather simple question is better understood, we will need much more theoretical discussion of how to relate genetic differences to taxonomic differences.Michael Jensen-Seaman Dr. Michael Jensen-Seaman recently graduated from Yale University. His dissertation research was on the evolutionary genetics of gorillas. He is currently a post-doctoral researcher at the University of Chicago.
Although nature tourism has been promoted as a sustainable, important and necessary "tool" for conserving species, it is now often viewed as a growing conservation problem. The number of well-documented cases linking nature tourism both to the loss of species and degradation of natural habitats is growing rapidly (Boo, 1990; Butler, 1991; Duffus, 1993; Ceballos- Lascurain, 1996).
Promoters of tourism on habituated, free-ranging gorillas state that the gorillas and their ecosystems will benefit if tourism generates significant revenues. This is an emotionally appealing, high-profile activity that can generate substantial revenue. It also appears to nicely bridge the gap between conservation and economic and social development objectives. Thus, ape tourism has been an 'easy sell' to almost everyone, not only politicians, donors and the public, but also conservationists (Harcourt, 1986; Vedder & Weber, 1990; Sholley, 1991; Stewart, 1991; Weber, 1993; McNeilage, 1996). The several serious problems inherent to tourism based on habituated, free-ranging gorillas are less publicised.
In a recent paper, we examined the benefits, problems and risks of gorilla tourism, and assessed whether this kind of tourism is likely to be a sustainable activity as now practised (Butynski & Kalina, 1998). Here we summarize the findings and conclusions for three of the topics examined in our review. These are: (1) the information base for the implementation and development of gorilla tourism; (2) the ability to control tourists and guides; and (3) the role of money and politics in gorilla tourism.
The sustainable use of natural resources requires the accumulation and assessment of information on the impact of use on the target population and ecosystem (Ack, 1991; Prescott-Allen & Prescott-Allen, 1996; SSN, 1996).
Since 1978, millions of dollars have been provided by donors to develop and support gorilla tourism. It is surprising, therefore, that little research has been conducted on the effects of tourism on gorilla behaviour, ecology, health and survival. This is especially so as all five current gorilla tourism programmes are based on small, restricted populations of 240-340 individuals that are already particularly vulnerable to extinction.
Here is one of numerous examples of the problem of insufficient data. There has been a sizeable loss of gorillas from one of the two tourist groups in the Bwindi-Impenetrable National Park, Uganda. The Katendegere group has declined from nine gorillas to three as a result of emigration and death (also, a tenth gorilla was born and died during this decline). In addition, this group now ranges 10 km east of where it occurred in 1993 prior to visits by tourists. Disturbance, stress and disease (scabies) related to tourism may be responsible for the decline in the size and considerable change in home range of this group. Unfortunately, the research vital to assessing the contribution of tourism to these changes was never undertaken.
The continued expansion of gorilla tourism in the absence of scientific information is not unique to the programme in the Bwindi-Impenetrable Forest. While there has been a long-term, extensive research programme on the gorillas of the Virunga Volcanoes, this work has focused almost solely on groups that are not part of the tourism programme. Nonetheless, the number of gorilla groups habituated for tourism in the Virungas increased from none in 1978 to 10 in 1997. Further, the official number of tourists visiting some groups has increased from six to eight, and an increase to 10 or more is being considered. This increase in the size of tourist groups was made despite strong recommendations by scientific advisers to keep group size limited to six people.
In addition to insufficient research data, all gorilla tourism programmes suffer from a total lack of comprehensive and independent risk assessments, environmental-impact studies, and programme evaluations. Under these circumstances, no one can advance models for sustainable gorilla tourism, or be confident that the gorilla tourism programmes are not now, or will not become, detrimental to the gorillas or their ecosystems.
Sustainable use will not occur unless effective regulatory structures are adopted and enforced (Ack, 1991; Prescott-Allen & Prescott-Allen, 1996). Gorilla-based tourism is exceptionally difficult to control, particularly over the long-term. That adequate control over gorilla tourism is often lacking is most clearly demonstrated by the many statements, photographs and videos of tourists and guides close to, or touching gorillas (e.g., McBride, 1988; Adams & Carwardine, 1993; Steele, 1994; Wagner, 1994; Schmitt, 1997). In some cases, tour operators and tourists pressure and bribe park staff to ignore the rules (Stewart, 1992; McNeilage, 1996; Macfie, 1997). In other cases, tourists are actively encouraged by park staff to break the rules and have more of a 'gorilla experience' than the regulations allow. The benefit to the guide is a larger gratuity at the end of the day.
Infringements of the regulations have been documented in all gorilla viewing programmes (Aveling, 1991; Stewart, 1992, 1993; McNeilage, 1996; Moulton & Sanderson, 1996; Macfie, 1997; Schmitt, 1997). The main concerns are physical contact between gorillas and tourists, extended visits with the gorillas (far beyond the 1 hour limit), large numbers of people in the tourist groups (up to least 32 people), twice-daily visits to groups of gorillas, visits by obviously sick tourists, and unauthorised visits to non-tourist gorilla groups.
The wide-spread perception is that gorilla tourism is guided by science and by concern for the survival of gorillas. A closer look, however, reveals that science frequently has little presence (see above) or influence, and that conservation is often relegated to a place behind politics, power struggles and short-term financial gains (Moulton & Sanderson, 1996).
For some politicians and tour operators, gorilla viewing is a bonanza from which to reap as much profit as possible. Not surprisingly, those calling for more science, for impartial evaluations, and for greater caution and restraint in the development and operation of gorilla tourism programmes have been routinely ignored, and sometimes targeted for attack by those bent on suppressing the problems in order to make political and monetary gains (McBride, 1988; Moulton & Sanderson, 1996). The high demand to see gorillas, and to obtain the money that gorilla tourism brings, are two extremely powerful and destabilising forces that seriously hamper efforts to make gorilla tourism sustainable.
The most recent and extensive data indicate that the 300-350 gorillas on the Virunga Volcanoes are the only representatives of the mountain gorilla subspecies Gorilla gorilla beringei (Sarmiento & Butynski, 1996; Sarmiento et al., 1996) - and that the gorillas of the Bwindi-Impenetrable Forest do not belong to this subspecies. One critical concern now is the suggestion to convert some or all of the three research (Karisoke) groups of gorillas in the Volcanoes National Park to tourism groups and/or to increase further the numbers of tourists visiting each group (D. Steklis, pers. comm.). If all three research groups become tourist groups, Rwanda would have six groups of gorillas available for tourism. This could increase to eight groups if the two habituated groups that emigrated to the Virunga National Park in the Democratic Republic of Congo expanded their range back into Rwanda. Under those circumstances, nearly all of the gorillas in the Volcanoes National Park, and about 70% of the world's remaining mountain gorillas, could be visited daily by more than 100 tourists, and by a similar number of guides, porters and rangers.
Whatever the risks associated with tourism on this small population now, these risks would be increased considerably. In addition, the valuable and well-known long-term research on these three groups would be severely restricted and jeopardized. Perhaps most importantly, the concept of gorilla tourism as a sustainable activity contributing to the survival of the Virunga gorillas would undoubtedly lose much credibility and support, not only from the international conservation community, but also from those tourists who thought they were benefiting gorilla conservation through their visits.
Another concern now involves the two new groups of gorillas under habituation for tourism in the Bwindi-Impenetrable Forest (Macfie, 1997). The home range of both groups lies entirely, or almost entirely, outside the "tourism zone" as agreed upon widely in the Tourism Plan (IGCP, 1992) and in the Bwindi Impenetrable National Park Management Plan (1995-1999) (Gubelman et al., 1995). Indeed, these groups live within a controlled research area where data on unhabituated gorillas were to be collected for use in assessing the impact of tourism on gorillas. This research and monitoring program, which according to the Tourism Plan was to begin in 1992 (IGCP, 1992), has not been initiated.
The expansion of the gorilla tourism programme in the Bwindi-Impenetrable Forest without sufficient baseline data, and without the benefit of professional, independent evaluation, is particularly worrying in light of the circumstances surrounding the decline of the Katendegere group (see above). This suggestion calls into question not only the sustainability of this programme, but also the veracity of one of the Tourism Plan's guiding principles, that "tourism is secondary to conservation."
In our review paper we conclude that tourism based upon gorilla viewing is not the conservation panacea that many people believe. There is too much emphasis now on generating revenues, while far too little attention is given to either demonstrating or ensuring the long-term sustainability of any of the five current gorilla tourism programmes. Tourism on free-ranging, habituated gorillas has been in effect for two decades, yet the recognized cornerstones to ensuring that this activity is sustainable have not been laid. There continues to be enormous disparity between what needs to be done and what the implementing governments, managers and supporting international conservation bodies are willing or able to accomplish.
Tourism based on small populations of gorillas is likely to be sustainable only:
If these basic pre-requisites cannot be met, then tourism on small populations of gorillas should be stopped until they can be met.
We are particularly concerned that all five of the established gorilla-viewing programmes are based on small populations of gorillas. Given the many problems and the management deficiencies observed, we suspect that gorilla tourism, as practised today, is likely to be sustainable only where gorilla populations are large. We suggest that limited tourism on the large lowland population of gorillas (14,550 gorillas; Hall et al., 1997) of the Kahuzi-Biega National Park and adjacent Itebero-Kasese region of eastern DRC would do little damage.
While tourism may contribute to the survival of some of these small populations of gorillas, it is at the same time undoubtedly putting them at additional risk. As a conservation priority, therefore, each of these programmes should be reviewed and evaluated thoroughly by multi-disciplinary teams of independent and impartial professionals. The teams should assesss whether these programmes can be made sustainable and specify how this might be achieved. Such an undertaking would bring to light more facts about gorilla tourism and further address the arguments, both for and against, that gorilla tourism has raised.
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