Post by Gorilla king on Aug 8, 2021 15:44:02 GMT -5
The Cross River gorilla (Gorilla gorilla diehli) is a subspecies of the western gorilla (Gorilla gorilla). It was named a new species in 1904 by Paul Matschie, a mammalian taxonomist working at the Humboldt University Zoological Museum in Berlin, but its populations were not systematically surveyed until 1987.[2][3]
It is the most western and northern form of gorilla, and is restricted to the forested hills and mountains of the Cameroon-Nigeria border region at the headwaters of the Cross River (Nigeria). It is separated by about 300 km (190 mi) from the nearest population of western lowland gorillas (Gorilla gorilla gorilla), and by around 250 km (160 mi) from the gorilla population in the Ebo Forest of Cameroon. Estimates from 2014 suggest that fewer than 250 mature Cross River gorillas remain, making them the world's rarest great ape.[1][4] Groups of these gorillas concentrate their activities in 11 localities across a 12,000 km2 (4,600 sq mi) range, though recent field surveys confirmed the presence of gorillas outside of their known localities suggesting a wider distribution within this range. This distribution is supported by genetic research, which has found evidence that many Cross River gorilla localities continue to maintain contact through the occasional dispersal of individuals.[5] In 2009, the Cross River gorilla was finally captured on professional video on a forested mountain in Cameroon.[4]
Description
The Cross River gorilla was first described as a new species of the western gorilla by Paul Matschie, a mammalian taxonomist, in 1904.[3] Its morphological distinctiveness was confirmed in 1987.[6] Subsequent analyses of cranial and tooth morphology, long bone proportions and distribution demonstrated the distinctiveness of the Cross River gorilla and it was described as a distinct subspecies in 2000.[7][8]
When comparing the Cross River gorilla to western lowland gorillas, they have noticeably smaller palates, smaller cranial vaults, and shorter skulls. The Cross River gorilla is not known to differ much in terms of body size or limb and bone length from western lowland gorillas. However, measurements taken from a male suggest that they have shorter hands and feet and have a larger opposability index than western lowland gorillas.[7]
According to Sarmiento and Oate's study published by the American Museum of Natural History, the Cross River gorilla has been described as having smaller dentitions, smaller palates, smaller cranial vaults, and shorter skulls than western lowland gorillas.[9] The Royal Belgian Institute of Natural Sciences depicted the Cross River gorilla as the largest living primate with a barrel-chest, relatively even hair, a bare black face and chest, small ears, bare shaped brows that are joined, and nostril margins that are raised.[3] They are clearly not the largest gorillas and the distinctiveness of their external characters still needs to be verified.[10] Other statistics include:
Average adult male height: 165–175 cm. (5 ft 5 in-5 ft 9 in).[3]Average adult male weight: 140–200 kg (310 lb-440 lb).[3]Average adult female height: 140 cm (4 ft 7 in).[3]Average adult female weight: 100 kg (220 lb).[3]
Evolution
In 2000 Esteban E. Sarmiento and John F. Oates proposed and supported the hypothesis that the Cross River gorilla began to evolve into a distinct subspecies of Gorilla gorilla during an arid period of the African Pleistocene phase in response to declining food sources and a greater emphasis on herbivory and terrestrial behaviors.[7]
The team stated that ancestors to the Cross River gorilla may have been secluded to the forests near the Cross River headwaters and/or elsewhere in the Cameroon highlands. They wrote that the Cross River gorillas may not have spread much since their isolation. The Gorilla gorilla gorilla ancestors differentiated from the Cross River gorilla by spreading beyond this area somewhere to the south and/or east of the Sanaga. Sarmiento and Oates stated that there is no evidence to suggest that G. g. gorilla and G. g. diehli are sympatric.[7]
Habitat
The Cross River gorilla, like many other gorilla subspecies, prefer a dense forest habitat that is uninhabited by humans. Due to the Cross River gorilla’s body size they require large and diverse areas of the forest to meet their habitat requirements. Similar to most endangered primates, their natural habitat exists where humans are often occupying and using for natural resources. Forests that are inhabited by the Cross River gorilla vary in altitude from approximately 100 to 2,037 metres (328 to 6,683 ft) above sea level.[11] Between 1996 and 1999, Field work was conducted on Afi Mountain in Cross River State, Nigeria for a period of 32 months. A great deal of data were collected, and things such as habitat types and topography mapped using line transects, climate, spatial and temporal availability of tree and herb foods and also the Cross River gorilla's wide range behavior, diet, and its grouping patterns. These data were all assessed from indirect evidence, such as feeding trails, nests, and feces.[12]
The habitats of the Cross River gorilla are negatively affected by the drastic deforestation and fragmentation of the land. These unfortunate events leave the gorilla species with few options for survival. As a result of deforestation and fragmentation, there are drastic reductions in carrying capacity, in other words, the size of the territories these animals inhabit has been significantly reduced. Because the population of humans living in this area is high, the amount of resources available to the Cross River gorillas is limited. Even though this decrease in the availability of land may appear to be a problem, research studies have found that an adequate amount of rainforest still remains that is suitable and comfortable for this subspecies. If, however, human pressures and activities towards deforestation continue, these territories will continue to diminish and ultimately will not exist. Additional examples of human activity that threaten Cross River gorillas and, of course, other species, are hunting, logging, agriculture, fuel wood harvesting, clearance of lands for plantation and exploitation of natural resources. Gorillas and other primates are only a small part of the larger ecosystem and thus, they rely on many aspects of their habitat for survival. Furthermore, also because of their body size, they lack ability to adapt to new environment and they have a rather slow reproductive rate. Even though there is somewhat of a limited research on Cross River gorillas, there is enough to conclude that these animals are currently able to sustain survival. What is still under debate is the total number of Cross River gorillas that exist.[13]
The Cross River gorilla is not only a critically endangered subspecies, as labeled by the IUCN, International Union for Conservation of Nature, but is under studied. The limited territories of their natural wildlife has led to that Cross River gorillas are approximately 200 kilometres (120 mi) away from other gorilla populations. This region is around the Nigeria-Cameroon border in which there are highland areas creating geographic restrictions for these gorillas. During the 20th century, Cross River Gorillas were known to roam low land localities, however, due to habitat loss and other human made factors such as resource exploitation, Cross River Gorillas were driven to inhabit only hill areas. This led to a decrease of resource availability as well as land availability. (Etiendem, 2013) Most of the habit regions for Cross River gorillas are legally protected due to their critically endangered status. However, there are still areas that are not like between the Kagwene Mountain and Upper Mbulu, and around Mone North.[14]
Behavior
A study published in 2007 in the American Journal of Primatology announced the discovery of the subspecies fighting back against possible threats from humans.[15] They "found several instances of gorillas throwing sticks and clumps of grass".[16] This is unusual.[17] When encountered by humans, gorillas usually flee and rarely charge.
Cross River gorillas have certain nesting behaviors (i.e. mean nest group size, style of the nest, location of the nest, and nest reuse patterns) that depend on things such as their current habitat, climate, food source availability and risk of attack or vulnerability. According to research done on the Cross River gorillas living in the Kagwene Gorilla Sanctuary, there is a high correlation between whether a nest is constructed on the ground or in a tree and the season. From April up until November, Cross River gorillas are more likely to build their nests within a tree, and from November on they are more likely to build it on the ground. Overall, it was found that more nests built at night were built on the ground as opposed to in trees. This species is also more likely to construct nests during the wet season than the dry season, as well as construct more arboreal nests in the wet season. It was found that day nest construction was more common, especially in the wet season. Reuse of nesting sites was also found to be common, although it did not have any relation to the season. And, their mean nest group size is from four to seven individuals. Although, nest group size varies depending on the location of the species.[19]
The groups of Cross River gorillas consist mainly of one male and six to seven females plus their offspring. Gorillas in lowlands are seen to have less offspring than those in the highlands. This is thought to be because of the hunting rate in the lowlands and infant mortality rate. The groups in the highlands are densely populated compared to those in the lowlands.[20]
The Cross River gorilla's diet consists largely of fruit, herbaceous vegetation, liana, and tree bark. Much like their nesting habits, what they eat is contingent on the season.[2] Observations of the gorilla indicate that it seems to prefer fruit, but will settle for other sources of nutrition during the dry season of about 4–5 months in northern regions.[21] Cross River gorillas eat more liana and tree bark throughout the year, and less fruit during dry periods of scarcity.[2]
Diet
The Cross River gorilla usually lives in small groups of 4-7 individuals with a few males and a few female members.[2] Their diet usually consists of fruit, but in fruit scarce months, (August–September, November–January) their diet is primarily made up of terrestrial herbs, and the bark and leaves of climber and trees. Many of the Cross River gorilla food sources are very seasonal and thus their diets are filled with very dense, nutritious vegetation that is usually found near their nesting sites. It was found that the Afi Mountain group of Cross River gorilla diet mostly consisted Aframomum spp. (Zingiberaceae) herbs, but when available in the wet season, they preferred to eat Amorphophallus difformis (Araceae) over the Aframomum, showing preference for certain foods that were seasonal and also an affinity to the vegetation that was only found in their habitat.[22]
Nesting
The nesting behavior of the Cross River gorilla was influenced by the environmental conditions, such as the climate, predation, herbaceous vegetation, absence of suitable nest building materials and seasonal fruits nearby. The gorillas did portray certain nesting habits like mean nest group sizes, size and type of nest created, as well as the reusing of certain nesting location nearby seasonal food sources. In Sunderland-Groves research on the nesting behavior of G. g. diehli at Kagwene Mountain they discovered that the nesting locations, whether on the ground or arboreal, were greatly influenced by the current season. During the dry season most of the nests were made on the ground, yet during the wet season the majority of the nests were made high in the trees, to provide protection from the rain. It was also found that the gorillas created more day nest during the wet season and reused nesting sites about 35% of the time. It was also found that the mean group size was 4-7 individual, yet the mean nest size at the sites was 12.4 nests and the most frequent number of nests was 13, showing some gorillas may have made multiple nests. The researchers also found nest sites with up to 26 nests, showing that sometimes multiple groups would nest together.[19]
Aggression
The Cross River gorilla at the Kagwene Mountain in Cameroon has been observed using tools and it seems to be unique to the population in this region. They have been observed in three separate cases, in which they threw grass at the researchers, a detached branch and in a third case, in which an encounter with a man who threw rocks at them led them to throw back fistfuls of grass. All the encounters had the gorillas in the group observe the researchers and react to their presence with vocalizations then led to calm behavior in the parts of the gorillas and finally an approach by the male gorillas and the throwing of grass at the researcher. The researchers have stated that this throwing behavior might have arisen due to human contact in the field and farms surrounding the mountain and the ambivalent nature of the gorillas is due to the surrounding people not hunting the gorillas due to the folklore about the gorillas.[15]
en.m.wikipedia.org/wiki/Cross_River_gorilla
It is the most western and northern form of gorilla, and is restricted to the forested hills and mountains of the Cameroon-Nigeria border region at the headwaters of the Cross River (Nigeria). It is separated by about 300 km (190 mi) from the nearest population of western lowland gorillas (Gorilla gorilla gorilla), and by around 250 km (160 mi) from the gorilla population in the Ebo Forest of Cameroon. Estimates from 2014 suggest that fewer than 250 mature Cross River gorillas remain, making them the world's rarest great ape.[1][4] Groups of these gorillas concentrate their activities in 11 localities across a 12,000 km2 (4,600 sq mi) range, though recent field surveys confirmed the presence of gorillas outside of their known localities suggesting a wider distribution within this range. This distribution is supported by genetic research, which has found evidence that many Cross River gorilla localities continue to maintain contact through the occasional dispersal of individuals.[5] In 2009, the Cross River gorilla was finally captured on professional video on a forested mountain in Cameroon.[4]
Description
The Cross River gorilla was first described as a new species of the western gorilla by Paul Matschie, a mammalian taxonomist, in 1904.[3] Its morphological distinctiveness was confirmed in 1987.[6] Subsequent analyses of cranial and tooth morphology, long bone proportions and distribution demonstrated the distinctiveness of the Cross River gorilla and it was described as a distinct subspecies in 2000.[7][8]
When comparing the Cross River gorilla to western lowland gorillas, they have noticeably smaller palates, smaller cranial vaults, and shorter skulls. The Cross River gorilla is not known to differ much in terms of body size or limb and bone length from western lowland gorillas. However, measurements taken from a male suggest that they have shorter hands and feet and have a larger opposability index than western lowland gorillas.[7]
According to Sarmiento and Oate's study published by the American Museum of Natural History, the Cross River gorilla has been described as having smaller dentitions, smaller palates, smaller cranial vaults, and shorter skulls than western lowland gorillas.[9] The Royal Belgian Institute of Natural Sciences depicted the Cross River gorilla as the largest living primate with a barrel-chest, relatively even hair, a bare black face and chest, small ears, bare shaped brows that are joined, and nostril margins that are raised.[3] They are clearly not the largest gorillas and the distinctiveness of their external characters still needs to be verified.[10] Other statistics include:
Average adult male height: 165–175 cm. (5 ft 5 in-5 ft 9 in).[3]Average adult male weight: 140–200 kg (310 lb-440 lb).[3]Average adult female height: 140 cm (4 ft 7 in).[3]Average adult female weight: 100 kg (220 lb).[3]
Evolution
In 2000 Esteban E. Sarmiento and John F. Oates proposed and supported the hypothesis that the Cross River gorilla began to evolve into a distinct subspecies of Gorilla gorilla during an arid period of the African Pleistocene phase in response to declining food sources and a greater emphasis on herbivory and terrestrial behaviors.[7]
The team stated that ancestors to the Cross River gorilla may have been secluded to the forests near the Cross River headwaters and/or elsewhere in the Cameroon highlands. They wrote that the Cross River gorillas may not have spread much since their isolation. The Gorilla gorilla gorilla ancestors differentiated from the Cross River gorilla by spreading beyond this area somewhere to the south and/or east of the Sanaga. Sarmiento and Oates stated that there is no evidence to suggest that G. g. gorilla and G. g. diehli are sympatric.[7]
Habitat
The Cross River gorilla, like many other gorilla subspecies, prefer a dense forest habitat that is uninhabited by humans. Due to the Cross River gorilla’s body size they require large and diverse areas of the forest to meet their habitat requirements. Similar to most endangered primates, their natural habitat exists where humans are often occupying and using for natural resources. Forests that are inhabited by the Cross River gorilla vary in altitude from approximately 100 to 2,037 metres (328 to 6,683 ft) above sea level.[11] Between 1996 and 1999, Field work was conducted on Afi Mountain in Cross River State, Nigeria for a period of 32 months. A great deal of data were collected, and things such as habitat types and topography mapped using line transects, climate, spatial and temporal availability of tree and herb foods and also the Cross River gorilla's wide range behavior, diet, and its grouping patterns. These data were all assessed from indirect evidence, such as feeding trails, nests, and feces.[12]
The habitats of the Cross River gorilla are negatively affected by the drastic deforestation and fragmentation of the land. These unfortunate events leave the gorilla species with few options for survival. As a result of deforestation and fragmentation, there are drastic reductions in carrying capacity, in other words, the size of the territories these animals inhabit has been significantly reduced. Because the population of humans living in this area is high, the amount of resources available to the Cross River gorillas is limited. Even though this decrease in the availability of land may appear to be a problem, research studies have found that an adequate amount of rainforest still remains that is suitable and comfortable for this subspecies. If, however, human pressures and activities towards deforestation continue, these territories will continue to diminish and ultimately will not exist. Additional examples of human activity that threaten Cross River gorillas and, of course, other species, are hunting, logging, agriculture, fuel wood harvesting, clearance of lands for plantation and exploitation of natural resources. Gorillas and other primates are only a small part of the larger ecosystem and thus, they rely on many aspects of their habitat for survival. Furthermore, also because of their body size, they lack ability to adapt to new environment and they have a rather slow reproductive rate. Even though there is somewhat of a limited research on Cross River gorillas, there is enough to conclude that these animals are currently able to sustain survival. What is still under debate is the total number of Cross River gorillas that exist.[13]
The Cross River gorilla is not only a critically endangered subspecies, as labeled by the IUCN, International Union for Conservation of Nature, but is under studied. The limited territories of their natural wildlife has led to that Cross River gorillas are approximately 200 kilometres (120 mi) away from other gorilla populations. This region is around the Nigeria-Cameroon border in which there are highland areas creating geographic restrictions for these gorillas. During the 20th century, Cross River Gorillas were known to roam low land localities, however, due to habitat loss and other human made factors such as resource exploitation, Cross River Gorillas were driven to inhabit only hill areas. This led to a decrease of resource availability as well as land availability. (Etiendem, 2013) Most of the habit regions for Cross River gorillas are legally protected due to their critically endangered status. However, there are still areas that are not like between the Kagwene Mountain and Upper Mbulu, and around Mone North.[14]
Behavior
A study published in 2007 in the American Journal of Primatology announced the discovery of the subspecies fighting back against possible threats from humans.[15] They "found several instances of gorillas throwing sticks and clumps of grass".[16] This is unusual.[17] When encountered by humans, gorillas usually flee and rarely charge.
Cross River gorillas have certain nesting behaviors (i.e. mean nest group size, style of the nest, location of the nest, and nest reuse patterns) that depend on things such as their current habitat, climate, food source availability and risk of attack or vulnerability. According to research done on the Cross River gorillas living in the Kagwene Gorilla Sanctuary, there is a high correlation between whether a nest is constructed on the ground or in a tree and the season. From April up until November, Cross River gorillas are more likely to build their nests within a tree, and from November on they are more likely to build it on the ground. Overall, it was found that more nests built at night were built on the ground as opposed to in trees. This species is also more likely to construct nests during the wet season than the dry season, as well as construct more arboreal nests in the wet season. It was found that day nest construction was more common, especially in the wet season. Reuse of nesting sites was also found to be common, although it did not have any relation to the season. And, their mean nest group size is from four to seven individuals. Although, nest group size varies depending on the location of the species.[19]
The groups of Cross River gorillas consist mainly of one male and six to seven females plus their offspring. Gorillas in lowlands are seen to have less offspring than those in the highlands. This is thought to be because of the hunting rate in the lowlands and infant mortality rate. The groups in the highlands are densely populated compared to those in the lowlands.[20]
The Cross River gorilla's diet consists largely of fruit, herbaceous vegetation, liana, and tree bark. Much like their nesting habits, what they eat is contingent on the season.[2] Observations of the gorilla indicate that it seems to prefer fruit, but will settle for other sources of nutrition during the dry season of about 4–5 months in northern regions.[21] Cross River gorillas eat more liana and tree bark throughout the year, and less fruit during dry periods of scarcity.[2]
Diet
The Cross River gorilla usually lives in small groups of 4-7 individuals with a few males and a few female members.[2] Their diet usually consists of fruit, but in fruit scarce months, (August–September, November–January) their diet is primarily made up of terrestrial herbs, and the bark and leaves of climber and trees. Many of the Cross River gorilla food sources are very seasonal and thus their diets are filled with very dense, nutritious vegetation that is usually found near their nesting sites. It was found that the Afi Mountain group of Cross River gorilla diet mostly consisted Aframomum spp. (Zingiberaceae) herbs, but when available in the wet season, they preferred to eat Amorphophallus difformis (Araceae) over the Aframomum, showing preference for certain foods that were seasonal and also an affinity to the vegetation that was only found in their habitat.[22]
Nesting
The nesting behavior of the Cross River gorilla was influenced by the environmental conditions, such as the climate, predation, herbaceous vegetation, absence of suitable nest building materials and seasonal fruits nearby. The gorillas did portray certain nesting habits like mean nest group sizes, size and type of nest created, as well as the reusing of certain nesting location nearby seasonal food sources. In Sunderland-Groves research on the nesting behavior of G. g. diehli at Kagwene Mountain they discovered that the nesting locations, whether on the ground or arboreal, were greatly influenced by the current season. During the dry season most of the nests were made on the ground, yet during the wet season the majority of the nests were made high in the trees, to provide protection from the rain. It was also found that the gorillas created more day nest during the wet season and reused nesting sites about 35% of the time. It was also found that the mean group size was 4-7 individual, yet the mean nest size at the sites was 12.4 nests and the most frequent number of nests was 13, showing some gorillas may have made multiple nests. The researchers also found nest sites with up to 26 nests, showing that sometimes multiple groups would nest together.[19]
Aggression
The Cross River gorilla at the Kagwene Mountain in Cameroon has been observed using tools and it seems to be unique to the population in this region. They have been observed in three separate cases, in which they threw grass at the researchers, a detached branch and in a third case, in which an encounter with a man who threw rocks at them led them to throw back fistfuls of grass. All the encounters had the gorillas in the group observe the researchers and react to their presence with vocalizations then led to calm behavior in the parts of the gorillas and finally an approach by the male gorillas and the throwing of grass at the researcher. The researchers have stated that this throwing behavior might have arisen due to human contact in the field and farms surrounding the mountain and the ambivalent nature of the gorillas is due to the surrounding people not hunting the gorillas due to the folklore about the gorillas.[15]
en.m.wikipedia.org/wiki/Cross_River_gorilla
I hope they can make a recovery 