This article gives an overview of Lowland gorilla habitat and social structure as well as a detailed description of their intestinal tract and wild vrs. captive diets.
Western Lowland Gorillas can be found in the subtropical and the tropical regions of Angola, Cameroon, Central African Republic, Gabon, Congo, and Nigeria. Gorillas are very misunderstood due to media but they are actually known as “Gentle Giant” or “Hairy Human.” A troop can cover a range from 1.16 to 5.79 miles of land in a single day. Their primary locomotion is called knuckle walking (Lang, 2005). They are covered in black, white, red and gray hair. The facial features will all remain the same until about the age of 10. Between the ages of 8 and 12 the males are called black backs. Most of them will not survive long enough for their fur to change into the silver coloring on their back due to premature death. The suporbital ridge and the sagittal nuchaecrest will begin to appear on their heads as will the silver on their back will begin to appear. These are secondary characteristics that will appear between the ages of 8 to 12 (Lang, 2005). The life span of these critically endangered caring creatures when in the wild is 30 years; this life span goes up by 40% in captivity, averaging from 40 to 50 years. (www.comozooconsevatory.org/como_zoo/animals/gorillaB.shtml).
Lowland gorillas live in troops ranging between 7 and 9 members with one silverback as the dominate male, while the remaining members are females and infants. Occasionally, a troop with two males may exist, in which case, the number of members will increase up to 18 to 21 members in a troop. (nationalzoo.si.edu/Animals/Primate/Facts/factsheets/Gorilla/default.cfm). To avoid inbreeding, the male adolescents will depart from his troop between 10 and 12 years of age, as long as they abide by the rules of the dominance hierarchy. However, if they do not abide, the silverback will send the Juvenal on his way out into the wild earlier than usual. When the dominate male decides to lie down for the evening, the entire troop will do what is referred to as nesting. The mothers and infants will bed together as the male will usually bed alone. Females may rest in trees or on the ground, while the juveniles prefer to play and rest amongst the trees and branches during this time. However, in some instances males have been observed sleeping within the group. When the male passes away, the entire troop disbands; the females will attempt to join another troop or may recruit a male as a dominant to begin their own troop. Both the female and the male can emigrate on their own or together. Females, however, have a greater opportunity of getting acceptance from another troop due to their breeding capabilities. Males, on the other hand, have a tougher time getting acceptance, as other silverbacks may reject them due to feeling threaten of losing their position in rank. A silverback may challenge another silverback, in an attempt receive a higher position within the hierarchy ranking, this may end in serious injury or death (Lang, 2005).
The mortality rate is averaged at about 38% which is due to infanticide, predator attacks, poachers, and the Ebola disease (Pin.primate.wisc/factsheets/entry/gorilla).(modified, Jan 29, 2009). They are considered to be critically endangered on the IUCNS Red List of Threatened Species.
The gestation period consists of eight and a half months, while copulation may occur all year long. The infant remains at the mothers’ side on average of 52 months. At this time the infant should already be weaned. Gorilla infant needs are identical to that of a human infant for the first year and half year of life (Lang, 2005).
DIGESTIVE PHYSIOLOGY OF GORILLAS
Humans and gorillas anatomically have very similar digestive systems, in which the only difference is the physiological make up and processes that are endure within the digestive system (Stevens and Hume, 1995).
First of all, digestion consists of breaking down food molecules through chemical processes in order to obtain the nutrients necessary for energy, growth, maintenance, and reproduction. Not all species have the same digestive system; this is because the anatomies of gastrointestinal and digestive systems are the result of adaptations from environmental pressures found within their habitat. These pressures can include chemical, physical, and nutritional properties of their diet. This parallelism of evolution adaptations shows a relationship between diet and digestion.
The digestion system of a gorilla (like humans) consists of four major processes, in order to digest food for the highest nutritional value. The first part is ingestion or eating. Next is digestion, in which the food is broken down by both chemical and mechanical processes. Third is absorption, which takes the digested food particles and disperse them to the cardiovascular and lymphatic system for cell distribution of essential nutrients. The last is defecation, the removal of indigestion products.
The primary difference of the digestive system between gorillas and humans is found in the gastrointestinal tract. Gorillas are herbivores so they need to be able to break down cellulose. Gorillas are known to be colon fermenters, which is defined as the anaerobic breakdown of organic compounds. Gorillas have large colons and the large intestine is filled with microbes (bacterial) and enzymes indigenous to the colon of the host, which destroy pathogenic microorganisms that are harmful to the host. Within gorillas it is believed that these bacteria serve the purpose of fermenting, detoxifying food, and breaking down cellulose (Stevens and Hume, 1995).
Fig 1. Gorilla Intestinal tract
Fig 2. Human Intestinal tract
This process of colon fermentation presents a symbolic relationship among the gastrointestinal microbes and their host. Scientists consider the importance and vitality of the functions of the colon fermentation and believe they can produce feeding management strategies that contribute to gorilla conservation and the success rate of the species.
The mean macronutrient can be broke down as fat=.05+.4, protein=11.8+8.2, available carbohydrate=7.7+6.3 and dietary fiber=74.0+12.9. Otherwise, 25% of energy as fat, 24.3% is protein, 15.8 % available carbohydrate, with potentially 57.3 % of metabolized energy from short-chained fatty acids derived from the colon fermentation of fiber (Popovich, etal, 1997).
In the wild, their diets contain very low fat but are high in fiber. They also consume less foliage and more fruit during the wet season (Williamson, 1988). For some reason, captive gorillas have high serum cholesterol levels, at 281 to 311 mgldl (McGuire, 1989). Captive gorillas also suffer from premature cardiovascular disease when they consume low fiber diets that contain meat and egg products (Cousins, 1979). Natural feeding patterns throughout the day may contribute to health benefits because increased feeding frequency has been shown to reduce LDC Cholesterol and post prandral insulin response (Jenkins, 1989).
***The diet of the gorillas at the Cheyenne Mountain Zoo is provided in detail here. This diet is: Bananas-2.5 lbs, Yams- 5.6 lbs (hand-fed), Carrots-5.5 lbs, Potatoes-2.2 lbs, and Assorted Greens-21.0 lbs, Mini Leaf-Eater Chow- 5.75 lbs, and Large Leaf-Eater Chow-1lb (hand fed). The green assortment contains a variety of leafy greens such as romaine and kale; it also includes bell pepper, zucchini, cucumber onion, broccoli, beans, and peas. The ingredients for the leaf-eater chow and mini-biscuits can be found at www.mazuri.com/PDF/5mo2-5672.PDF . Each gorilla receives 49.3 lbs a day of diet listed above. These feedings are spread out though out the day and at various times. The gorillas get fed between 6 and 7 times per day. The diet presentation is alternated daily. Sunday- pasta instead of yam, Monday- frozen bananas, Tuesday- cooked yams, Wednesday- spices on diet, Thursday- Keepers’ choice (can be nothing different with the diet), Friday-diet given in boxes or in grain bags, Saturday-diets cut up into tiny pieces. This is the regular diet and doesn’t include any extra items that may be given as enrichment (Hoolingworth, 2009).