Male western gorilla ( Gorilla gorilla )
|I. Geoffroy Saint-Hilaire , 1852|
The gorillas ( Gorilla ) are a primate genus in the family of great apes (hominids). They are the largest living primates and the most pronounced leaf eater among the great apes. They are characterized by their black-gray fur and stocky build and live in the central parts of Africa . In the past, all animals were grouped into one species, but more recent classifications differentiate between two species, each with two subspecies: the western gorilla ( G. gorilla ), the western lowland gorilla ( G. g. Gorilla ) and the cross-river gorilla ( G g. diehli ) and the eastern gorilla ( G. beringei ), which distinguishes between the eastern lowland gorilla ( G. b. graueri ) and the mountain gorilla ( G. b. beringei ).
Build and dimensions
Gorillas have a robust, stocky build. They are standing about 1.25 to 1.75 meters high, usually keeping their knees slightly bent. Like all great apes, they are tailless. In terms of weight, they show a clear sexual dimorphism : while females weigh 70 to 90 kilograms, males can reach up to 200 kilograms. Despite reports to the contrary (some sources give up to 275 kilograms), animals weighing more than 200 kilograms are considered rare in the wild. Well-fed animals in human care, on the other hand, can become significantly heavier and weigh up to 350 kilograms. Eastern gorillas are generally slightly larger and heavier than western gorillas, they have a wider chest and appear stockier.
As with all great apes with the exception of humans , the arms are significantly longer than the legs, the span of the outstretched arms is 2 to 2.75 meters. Gorillas have very broad hands with large thumbs. The feet are also wide, the big toe can be opposed , as with most primates . In the mountain gorilla - the subspecies most heavily living on the ground - however, this is less splayed and connected to the other toes by connective tissue. Like humans (and other primates, too) every gorilla has a distinctive fingerprint . Scientists identify the animals primarily on the basis of photos or drawings of their equally unique "nose print", that is, through the shape of the nose and the arrangement of the folds on it.
The fur color of the gorillas is dark. While the eastern gorillas are black, the western gorillas are more gray-brown; in this species the top of the head can be conspicuously brown in color. The face, ears, palms and soles of the feet and, in older males, the chest are hairless. In return, older males develop a silver-gray back fur, which is why they are also known as silverbacks . While in the eastern gorillas this gray coloration is limited to the back, in western gorillas it can also extend to the hips and thighs. Mountain gorillas have longer and silky fur than other populations, especially on the arms.
Head and teeth
The head of the gorilla is characterized by its short snout compared to other primates; the nostrils are large, but the eyes and ears are small. The pronounced bulges above the eyes are striking, the skulls of the males are also equipped with a crest and a nuchal ridge (a bone ridge on the neck), which serve as muscle attachment points.
Like all Old World monkeys , gorillas have 32 teeth, the tooth formula is I 2- C 1- P 2- M 3. As in many leaf-eating mammals, the incisors are relatively small, the canines are large and tusk-like and in males significantly larger than in females. The molars have higher cusps and sharper shear edges than in other great apes, which is also an adaptation to the leaf food.
The eye color is uniformly brown, the iris has a black ring on its edge.
Distribution area and habitat
Gorillas live in central Africa and, like the chimpanzees, only live north of the Congo River . However, the distribution areas of the two gorilla species are around 1000 kilometers apart. Western gorillas live near the Gulf of Guinea , with the Cross River gorilla only inhabiting a small area in the border region between Nigeria and Cameroon . Western lowland gorillas are distributed from southern Cameroon and the west of the Central African Republic via Equatorial Guinea , Gabon and the Republic of the Congo to the Angolan enclave of Cabinda . The population in the far west of the Democratic Republic of the Congo is believed to have died out.
Eastern gorillas inhabit the eastern regions of the Democratic Republic of the Congo (Eastern lowland gorillas) as well as the regions of the Virunga volcanoes and the Bwindi forest in the border area between Uganda , Rwanda and the Democratic Republic of the Congo (mountain gorilla).
Gorillas are pronounced forest dwellers. Western lowland gorillas prefer the lowland rainforests and wetlands, while cross-river and eastern lowland gorillas tend to be found in hilly terrain. The mountain gorillas are the most distinctive inhabitants of the mountainous country and occur in regions up to 4000 meters above sea level. Different populations inhabit different forest types - also within the subspecies, in general Eastern gorillas are more often found in secondary forests .
Way of life
Movement and activity times
Gorillas can forage for food both on the ground and in the trees. On the ground they move like chimpanzees in a quadruped ankle gait , that is, they rely on the second and third phalanxes. They rarely walk alone on their feet, but they only cover short distances. Gorillas are also relatively good climbers and climb trees up to 40 meters high. In contrast to chimpanzees and orangutans, however, they very rarely adopt a suspensory (hanging on the arms) posture in the branches. The mountain gorillas, on the other hand, with the exception of humans, are the most pronounced ground dwellers of all great apes and rarely climb trees.
Although gorillas cannot swim, they often come to the beach in the Gamba nature reserve in Gabon and have also been seen swimming in the sea. The so-called Bai gorillas in the Congo habitually wade through the swamps of the clearings they visit in search of food and are not particularly afraid of water. However, gorillas do not cross bodies of water, especially rivers where they cannot stand upright.
Like all great apes are diurnal gorillas, almost all of their activity is limited to the time 6:00 to 18:00 AM. After eating in the morning, they take a break between 10:00 and 14:00 in order to then go looking for food again and prepare a place to sleep. The sleeping places consist of self-made nests made of branches and leaves, which can either be on the ground or in the branches. It takes no more than five minutes to make the nests, and usually a nest is only used for one night.
Gorillas live together in groups that can range from two to 40 animals. The group size of the western gorillas with an average of four to eight animals is significantly smaller than that of the mountain gorillas with ten to 20 individuals. Generally, there is only one fully grown silverback male in each group, rarely two or three. In this case, a male takes on the dominant role and is the only one that reproduces. Several females and their offspring, and usually one or more subadult males (" black back "), complete the group.
Sometimes a “fission fusion model” (“separating and coming together”) can be observed, which means that the group repeatedly divides into smaller subgroups - for example to search for food - and then comes back together again. The observations on group behavior are not uniform, but overall the groups are likely to be stable and the cohesion closer than, for example, with chimpanzees.
In contrast to many other primates, in the gorillas not only the males but also the females leave their birth group when they grow up. As a result, the females in a group are usually not related to one another and only interact with one another to a very limited extent. A social organization around a “core group” of closely related females, as can be observed in many other primates, is missing in the gorillas. Males who have left their birth group usually wander around alone for a few years and then try to either start their own group by rallying a few females or to take on the leadership role in an established group. If they succeed in this, infanticide often occurs , that is, the male kills the young animals conceived by his "predecessor". The benefit of this behavior can be seen in the fact that lactating females do not become pregnant, but are quickly able to conceive again after the young animal dies.
In contrast to the males, the females do not remain alone for long after leaving their birth group, but rather try to quickly join an existing group or a young male. It can happen, however, that the females of an established group join forces to drive away a newly arrived female.
Territorial behavior and dealing with other groups
The size of the home ranges is variable, but with lowland gorillas they are larger with 500 to 3200 hectares than with mountain gorillas with 400 to 800 hectares. The habitat behavior is little developed, the grazing areas often overlap. However, the groups may have core areas that other groups will not enter.
Often several groups search for food in the same place, but not at the same time. Usually the groups avoid direct contact with each other and avoid each other; Other observations have shown that when two groups meet, they can also temporarily merge or become hostile. This is carried out through roars, gestures or demonstrations of strength, but gorillas usually avoid physical arguments.
Gorillas communicate with one another through sounds, facial expressions, postures, and demonstrations of strength.
You are familiar with a number of sounds that are used to locate group members and foreign groups and to express aggression. These include belching sounds, which are used to establish contact with other group members, loud "U!" Calls ("hoots") that can be heard over a kilometer , which express the dominance of the male or enable contact between individual groups, as well as grunts and growls expressing aggression. This mood can also be signaled with an open mouth and bared teeth, for example. On the other hand, a muffled, drawn out grunt (not unlike a human throat clearing) testifies to relaxation and wellbeing, which rangers and tourists like to imitate to signal their peaceful intentions.
The best known communicative behavior of the gorillas is drumming on the chest. It used to be thought of as a purely male behavior that serves to show off and should intimidate other males. However, this behavior is practiced by animals of both sexes and all age groups and probably serves various functions, such as indicating the location or as a greeting ritual.
Behavioral patterns that serve to intimidate include, in addition to loud roaring, walking on two legs, shaking branches, tearing up and throwing plants away (mostly in the direction of the supposed opponent) and hitting the ground.
Until recently, tool use was not known in wild gorillas. In 2005, however, animals were photographed for the first time using a stick to sound out the depth of a body of water before they crossed it, and which placed a piece of wood as a bridge on marshy terrain to make it easier to pass. However, there is still no known use of tools by gorillas in direct connection with food acquisition. Their great strength, with which they can break even thick branches, and their diet, which is mainly based on leaves and fruits, should make such methods as can be observed in other great apes unnecessary.
Like chimpanzees , gorillas use prickly, tannic leaves to rid themselves of annoying intestinal parasites. They eat a large number of these leaves whole, so that they scrape the parasites off the intestinal walls.
Interaction with other species
Adult gorillas have no natural predators; Young animals occasionally fall prey to leopards . Parts of their range can overlap with that of the common chimpanzee ( sympatry ). Similar lifestyles and eating patterns could lead to food competition, but there are no observations on this. The greatest threat to the gorillas comes from humans due to habitat destruction and hunting (see threats ).
Of all great apes, gorillas are the most pronounced herbivores. Their main food is leaves , depending on the type and season they also eat fruit to a different extent . Because of their size and the low calorific value of their food, gorillas have to spend a lot of their active periods eating.
Mountain gorillas feed mostly on leaves and pulp ; Fruits, on the other hand, are hardly consumed. The two lowland gorilla populations, on the other hand, supplement their diet with fruits, which can make up up to 50% of the diet, depending on the season. For this reason, lowland gorillas climb trees more often, while mountain gorillas are pronounced ground dwellers.
It is unclear to what extent insects and other small animals are consumed. Meat-eating has rarely been seen in the wild, but there have been reports that western lowland gorillas broke termite mounds and ate the insects. Gorillas may also inadvertently ingest small animals when they are on the leaves they have eaten.
Gorillas rarely drink water. They satisfy their need for fluids simply by consuming large amounts of plant-based food - an average of 25 kilograms per day in adult males.
The daily forays that the gorillas make in search of food are short compared to those of other primates. These are shortest for mountain gorillas with an average of 0.4 kilometers, which is due to the abundance of leaves and the low nutritional value of this food, which the animals compensate for with long periods of rest. The daily forays of the lowland gorillas are much longer with 0.5 to 1.2 kilometers due to the more varied food.
Reproduction and development
The mating behavior of the gorillas is polygynous , ie only the dominant male reproduces with the females of the group. However, there are always exceptions to this rule for various reasons (see mating behavior ). Mating is not seasonally restricted, so it can take place all year round. The length of the female's sexual cycle is 27 to 28 days. The gestation period is about 8½ to 9 months and is therefore together with that of humans the longest of all primates.
Usually a single young is born, twins are rare. Newborns weigh around 2 kilograms, at three months they can crawl and then ride on their mother's back for several years. They are weaned after three to four years. Accordingly, the birth interval is 3.5 to 4.5 years - unless the young animal dies earlier. Observations have shown that the mortality rate in young animals is 42%, and it is particularly high in the first year of life. In the course of its life, the female gives birth to an average of two to three surviving young animals.
Females reach sexual maturity at six to eight years old and males at ten. Due to the social structure, the first mating usually takes place a few years later: in females with nine to ten years and in males with 15 years.
The life expectancy of the animals is 35 to 40 years, but in human care gorillas can live to be older than 50. Massa († 1984) at the Philadelphia Zoo was the oldest known gorilla in the world at the age of 54, followed by Jenny († 2008) at the Dallas Zoo at the age of 55. Until January 2017, Colo (* December 22, 1956; † January 17, 2017) was the oldest living animal in the Columbus Zoo . She was also the first gorilla ever born in captivity. On August 20, 2018, the gorilla Fritz, who was probably 55 years old, was euthanized in Nuremberg Zoo, who was born in the Cameroon jungle in 1963 and captured as a baby.
Gorillas and humans
History of discovery and research
The Carthaginian seafarer Hanno († 440 BC) brought the skins of three "wild women" with him from his trip to Africa, who were referred to as Γοριλλαι Gorillai by the African interpreters . It is unclear where exactly Hanno killed the creatures and whether they were really gorillas, or chimpanzees or even members of a pygmy people .
Apart from a 16th century report by the English navigator Andrew Battell, the western world did not become aware of these animals until the 19th century. The name "gorilla" was first assigned to these animals by the US missionary, doctor and naturalist Thomas Staughton Savage (1804–1880) based on the Hannos report, with the assistance of the American naturalist and anatomist Jeffries Wyman (1814–1874). Savage, who had received some shot specimens of the western lowland gorilla in Gabon , described these great apes as a new species in 1847 together with Wyman; the first scientific species name was Troglodytes gorilla ( Troglodytes was the genus name of chimpanzees at that time ). Isidore Geoffroy Saint-Hilaire then coined the generic name Gorilla, which is still valid today, in 1852 .
The Africa researcher Paul Belloni Du Chaillu (1835–1903) caused through his undertakings and his publications that towards the end of the 19th century interest in gorillas in the USA and also in Europe increased rapidly. The first living gorilla in Europe to be scientifically examined in detail, called M'Pungu , was exhibited in the Berlin Aquarium Unter den Linden in 1876/77 . One of the best-known motifs is the film character " King Kong ", a gigantic gorilla, who has returned in numerous adaptations and remakes in film and television history since the first film King Kong and the white woman in 1933. This figure, like many other gorilla figures from books, comics or films, has little in common with the real gorillas, not just in terms of size but also behavior. This was because the way of life and social behavior of these animals was little known for a long time.
At first, as with many mammals, the focus was on morphological studies. Paul Matschie suspected in 1903 that an animal killed on the Virunga volcanoes could be a separate species ( mountain gorilla ). He described a few more species, however, through the work of Ernst Schwarz and Harold Coolidge in the 1930s, the system that was valid until the end of the 20th century was established with a single species and several subspecies. It was only at the beginning of the 21st century, based on morphological and molecular studies, that the view prevailed that there are two types of gorillas. (See also internal systematics .)
The way of life of the gorillas only moved into the focus of research after the Second World War. The American George Schaller (* 1933) was the first researcher to extensively investigate wild gorillas from 1959. In 1967, Dian Fossey (1932–1985) - supported by Louis Leakey - began researching the mountain gorillas on the Virunga volcanoes for decades . Her life and murder became known to a wider public through the filming of Gorillas in the Fog . Field studies in western lowland gorillas did not begin until the 1980s; the most famous project is the work of Caroline Tutin and Michael Fernandez in the Lopé National Park in Gabon .
As with other great apes, attempts are also made in gorillas to research their communication skills and intelligence in laboratory tests. One of the most famous of these investigations is the attempt to teach the female Koko the American sign language.
Both gorilla species are threatened, albeit to different degrees. One reason for the endangerment is the destruction of their habitat by clearing the forests. In addition, there are civil war-like conditions in parts of their area of distribution, which make the necessary protective measures difficult and make efficient monitoring of protected areas almost impossible. Another reason is hunting for their meat (" bushmeat "), which is still carried out. Diseases, especially Ebola, continue to affect populations that have already been attacked . The total population of gorillas is estimated at around 365,000 animals, which, however, are distributed very differently between the individual populations.
- The western lowland gorilla is by far the most common subspecies. Their population was estimated at around 360,000 animals for 2013. Today, this value is considered to be questionable, as lower populations can be assumed due to habitat degradation, poaching and the decimation by the Ebola virus .
This population of the western lowland gorilla inhabits a large, comparatively sparsely populated area, in which some national parks have also been established. In addition, almost all gorillas kept in zoos are western lowland gorillas, where after decades of difficulties, breeding is now regularly successful.
- The cross-river gorilla , the second subspecies of the western gorilla , inhabits a small area in the border region between Nigeria and Cameroon . Human settlement activity has split its area of distribution into around ten small areas, the total population is estimated at 250 to 300 animals. The IUCN lists this subspecies as " critically endangered" .
- The eastern lowland gorilla lives in the east of the Democratic Republic of the Congo , the largest population lives in the Kahuzi-Biéga National Park . The civil war in this region and the mining of the ore coltan are the main reasons that protective measures for this subspecies are not sufficiently implemented. The IUCN estimated the total population in 2000 to be 8,000 to 17,000 animals, the environmental foundation WWF only assumed a maximum of 5,000 animals in 2009. For 2015 both estimate the population at 3,800 individuals.
- The mountain gorilla occurs in two separate populations in the Virunga National Park and in the Bwindi Impenetrable National Park . Supported by the strong media presence of this subspecies, protective measures have led to a slight increase in populations. Today there are around 1000 animals, around 400 of them in the Bwindi National Park. Nevertheless, the subspecies is still listed as "critically endangered".
Gorillas have been listed in Appendix I of the Washington Convention on Species Protection since 1975 . International commercial trade in the animals or their parts is therefore prohibited. In 2008 the agreement for the conservation of gorillas and their habitats came into force. The agreement has so far been signed by the Central African Republic , the Republic of the Congo , Nigeria , the Democratic Republic of the Congo , Rwanda and Gabon .
In order to draw attention to the threat to these great ape species, the UN declared 2009 the International Year of the Gorilla .
Gorillas together with orangutans , chimpanzees ( Common Chimpanzee and Bonobo ) and the people , the family of great apes (hominids). Although gorillas have a number of morphological similarities with chimpanzees, these are probably synapomorphies (common derived characteristics) of all African great apes that have been lost in humans. Genetic studies suggest that chimpanzees are more closely related to humans than to gorillas. This is expressed in the cladogram (see fig.).
The proposal formulated by some researchers around the year 2000 to assign gorillas and chimpanzees to the genus Homo due to the only minor genetic differences between them and humans was not included in the internationally renowned systematic works in the following years.
When the line of development leading to the gorillas separated from the line leading to the chimpanzees and humans has not yet been clearly established: the alleged gorilla ancestor Chororapithecus was dated around 8 million years ago, but based on DNA analyzes , the separation was in dated 6.5 million years ago. The separation of the western gorilla and the eastern gorilla occurred around 1.6 to 0.9 million years ago, the separation of the western lowland gorilla from the cross-river gorilla around 17,800 years ago.
The sequencing of the gorilla genome and the comparison with that of the human and the chimpanzee showed that in about 15% of the 1 Mbp sections the human is more similar to the gorrila than the chimpanzee and the chimpanzee is more similar to the gorilla than the human , together 30%. On average, however, the result is clear: the mean difference (“mean nucleotide divergences”) is 1.75% between gorillas and humans and 1.37% between humans and chimpanzees. Accordingly, humans are more closely related to the chimpanzee than to the gorilla.
In 2017, DNA sequences in the core genome (nuclear DNA) were examined in more detail, which are relicts of sequences previously taken over from the mitochondrial genome ( mtDNA ) (so-called nuclear mt sequences, NUMT) in the form of functionless pseudogenes in humans and, similarly, in chimpanzees and can be found in the gorilla. A comparison of these NUMT versions with each other and with the mtDNA of these three species shows two things: The NUMT pseudogene was created around the time the lines to gorilla and human / chimpanzee were separated, and it is clearly different from all three mtDNAs, corresponding to one Evolution over about 4.5 million years. Two scenarios are compatible with this finding, both of which postulate a fourth hominine species, which has since become extinct, as well as multiple hybridization between species that had already diverged over several million years.
A hybridization between the line to the gorilla with that to the human / chimpanzee with subsequent introgression in the latter line (30% above) was even considered to be the cause of the split between chimpanzee and human and individual gorilla traits in human lines.
Traditionally, all gorillas were grouped into one species and three subspecies were distinguished, the western lowland gorilla, the eastern lowland gorilla and the mountain gorilla.
Due to differences in body structure and way of life, we now assume two species, each with two subspecies:
- Western gorilla ( Gorilla gorilla )
- Eastern gorilla ( Gorilla beringei )
The population of the Bwindi forest ("Bwindigorillas"), which is traditionally assigned to the mountain gorilla, could, however, represent a separate subspecies of the Eastern gorilla, which has not yet been scientifically described.
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