Temporal range: Late Miocene to Recent
|Maxwell's duiker, Cephalophus maxwellii|
Their name comes from the Dutch word for diver which refers to their practice of diving into tangles of shrubbery. Duikers are split into two groups based on their habitat: forest and bush duikers. All forest species inhabit the rainforests of Sub-Saharan Africa, while the only known bush duiker, grey common duiker occupies savannas. Duikers are very shy, elusive creatures with a fondness of dense covers. Bush duikers that tend to live in more open areas, for example, are quick to disappear into thickets for protection.
Because of their rarity and interspersed population, there is not much known about duikers; thus, further generalizations are widely based on the most commonly studied red forest, blue, yellow-backed and the common grey duiker. In tropical rainforest zones of Africa, people non-selectively hunt duikers for their fur, meat, and horns at highly unsustainable rates. Population trends for all species of duikers, excluding the common duiker and the smallest blue duiker, are significantly decreasing; Aders' and particularly the larger duiker species such as the Jentink’s and Abbott’s duikers, are now considered endangered by the IUCN Red List of Threatened Species .
Anatomy and Physiology
Duikers range from the 3 kilogram blue duiker to the 70 kilogram yellow-backed duiker. With their body low to the ground and with very short horns, forest duikers are built to effectively navigate through dense rainforests and quickly dive into bushes when threatened. Since the common grey duiker live in more open areas like savannas, they have longer legs and vertical horns that allow them to run faster and for longer distances; only the males, who are more confrontational and territorial, exhibit horns. Also, duikers have well-developed preorbital glands that resemble slits under their eyes, or in the cases of blue duikers, pedal glands on their hooves. Males use secretions from these glands to mark their territory.
Besides reproduction, duikers behave in highly independent manner and prefer to act alone. This may, in part, explain the limited sexual size dimorphism shown by most duiker species, excluding the common grey duiker in which the females are distinctly larger than the males.
Also, body size is proportional to the amount of food intake and the size of food. Anatomical features such as “the head and neck shape” also limit the amount and size of food intake. “Anatomical variations... impose further constraints on ingestion” causing differences in the food sources among different species of duiker.
In 2001, Helen Newing’s study in West Africa on the interactions of duikers found that body size, “habitat preference, and activity patterns” were the main differentiating factors among the seven species of duikers. These differences specific to each species of duiker allow them to coexist by "limiting niche overlap". However, although some species are yet to be considered ‘endangered’, because of the repeated damage and fragment of their habitat by human activities, such specialization of the niches are gradually becoming impaired and are contributing to the significant decrease in population.
Due to their relative size and reserved nature, duikers’ primary defense mechanism is to hide from predators. Duikers are known for their extreme shyness, freezing at the slightest sign of a threat and diving into the nearest bush. Duikers’ “social behavior” is also known to maintain “[sufficient distance] between” any other individual. However, in contrast to their conserved nature, duikers are more aggressive when dealing with territories; they mark their territory as well as their mates with secretions from their pre-orbital glands and fight other duikers that challenge their authorities. Male common grey duikers, especially the younger males, mark their territory also by defecation.
For those duikers that travel alone, they choose to interact with other duikers once or twice a year, solely for the purpose of mating. Although duikers occasionally form temporary groups to “gather…fallen fruit”, because so little is known about how duikers interact and affect one another, it is difficult to determine which factors contribute the most to their endangerment.
Duikers prefer to live alone or as pairs in order to avoid the competition that comes from living in a large group. They have also evolved to become highly selective feeders, feeding only on specific parts of plants. In fact, in his study regarding the relationship between “group size and feeding style”, P.J. Jarman found that the more selective an organism’s diet is, the more dispersed their food will be, and consequently, the smaller the group becomes.
Duikers are primarily browsers, meaning they mainly feed on seeds and fruits; however, on occasion, they feed on animal matter. While they feed on a wide range of plants, they choose to eat specific parts of the plant that are most nutritious. Therefore, in order to feed efficiently, they must be familiar with their territory and be thoroughly acquainted with the geography and distribution of specific plants. For such reasons, it is not easy for duikers to readjust to novel environments created by human settlements and deforestation.
The smaller duikers, like the blue duiker, generally tend to eat various seeds, while larger duikers tend to feast more upon larger fruits. Since blue duiker are very small in size, they are “more efficient [in] digesting small, high quality items”. Receiving most of their water from the foods they eat, duikers do not rely on drinking water and can “be found in waterless localities”. They are primarily browsers rather than grazers, eating leaves, shoots, seeds, fruit, buds and bark, and often following flocks of birds or troops of monkeys to take advantage of the fruit they drop. They supplement their diets with meat: duikers consume insects and carrion from time to time and even manage to capture rodents or small birds. Since food is the deciding factor, various locations of food sources often dictate the distribution of duikers.
Duikers can be diurnal, nocturnal or both. Since the majority of the food source is available in the daytime, duiker evolution has rendered most duikers as diurnal. A study done by Helen Newing in 2001 found that a correlation exists between body size and sleep pattern in duikers. While smaller to medium sized duikers show increased activity and scavenge for food during the daytime, larger duikers are most active at night. In exception, Yellow-backed duikers, the largest duker species, are active during both day and night.
Distribution and Abundance
Duikers are found sympatrically in many different regions. Most species of duikers dwell in the tropical rainforests of Central and West Africa, creating overlapping regions among different species of forest duikers. Although "body size is the primary factor in defining the fundamental niches of each species", often dictating the distribution and abundance of duikers in a given habitat, it is often hard to distinguish between the numerous species of duikers based purely on distribution and abundance. For example, the blue duiker and red forest duiker live in coexistence within the small area of Mossapoula, Central African Republic. But while blue duikers are seen more frequently than red forest duikers “in the heavily hunted area of Mossapoula, Central African Republic", red forest duikers are more observed in a less exploited regions such as the western Dja Reserve, Cameroon.
Conservation of duikers has a direct and critical relationship with their ecology. Disruption of balance in the system leads to unprecedented competition, both interspecific and intraspecific. Before intervention, the system of specialized resources in which larger duikers exploit a particular type of food and smaller duikers on another, is functional as modeled in the diurnal and nocturnal nature of the duikers; This allows the niche to be shared by others without distinct interspecific competition. Similarly, they decrease intraspecific competition by being solitary, independent and selective in eating habits. In consequence, disruption of the competitive balance in one habitat often cascades its effect on to the competitive balance in another habitat.
Also, as indicated by the study of Helen Newing, there is a correlation between body size and diet. Larger animals have more robust digestive systems, stronger jaws, and wider necks that allow them to consume lower quality foods, larger fruits and seeds.
Similarly, Bay and Peters's duiker can coexist because of their different sleep patterns. This allows the Peters's duiker to eat its fruits by day, and the Bay duiker to eat what is left by night. In consequence of such life pattern, Bay duiker’s digestive system has evolved to consume remaining, rather poor-quality foods.
One other critical influence duikers have on the environment includes acting as “seed dispersers for some plants”. Duikers and such plants maintain a mutualistic relationship, the plant serving as a nutritious and abundant food source for duikers, and benefiting from the extensive dispersal of their seeds by the duikers at the same time.
Duikers live in an environment where even a subtle change in their life pattern can greatly impact the surrounding ecosystem. Two of the main factors that directly lead to duiker extinction are “habitat loss” and overexploitation. Constant urbanization and the process of “shifting agriculture” is gradually taking over many of duikers’ habitats; at the same time, overexploitation is also permitting the overgrowth of other interacting species, resulting in an inevitable disruption of coexistence.
Overexploitation of duikers affects their population as well as organisms that rely on them for survival. For instance, plants that depend on duikers for seed dispersal may lose their primary purpose of reproduction, and other organisms that depend on these particular plants as their resources would also be usurped of their major source of food.
Duikers are often captured for bushmeat. In fact, duikers are one of the most hunted animals “both in terms of number and biomass” in Central Africa. For example, in areas near the African rain forests, because people do not raise their own livestock, “bushmeat is what most people of all classes rely on as their source of protein” For these people, if the trend of overexploitation continues at such high rate, the effects of the population decrease in duikers will be too severe for these organisms to serve as a reliable food source.
In addition to the unnaturally high demand for bushmeat, unenforced hunting law is a perpetual threat to many species, including the duiker. In a study done by Anadu and others in 1988, they found that most hunters believe the diminishing number of animals is due to overexploitation. “The direct effects of hunting consist of two main aspects: overexploitation of target species, and incidental hunting of non-targeted or rare species because hunting is largely non-selective”.
To avoid this outcome, viable methods of conserving duikers are access restriction and captive breeding. Access restriction involves imposing "temporal or spatial restrictions" on hunting duikers. Temporal restrictions include closing off certain seasons, such as the main birth season, to hunting; spatial restrictions include closing off certain regions where endangered duikers are found. Captive breeding has been utilized and is often looked as a solution to ensuring the survival of the duiker population; however, due to the duikers’ low reproductive rate, even with the protection provided by the conservationists, captive breeding would not increase the overall population’s growth rate.
The greatest challenges facing the conservation of duikers are the lack of sufficient knowledge regarding these organisms coupled with their unique population dynamics. We need to not only thoroughly understand their population dynamics but also establish methods to differentiate among the various species.
- Subfamily Cephalophinae
- Genus Cephalophus
- Abbott's duiker, C. spadix
- Ader's duiker, C. adersi
- Bay duiker, C. dorsalis
- Black duiker, C. niger
- Black-fronted duiker, C. nigrifrons
- Brooke's duiker, C. brookei
- Harvey's duiker, C. harveyi
- Jentink's duiker, C. jentinki
- Ogilby's duiker, C. ogilbyi
- Peters's duiker, C. callipygus
- Red-flanked duiker, C. rufilatus
- Red forest duiker, C. natalensis
- Ruwenzori duiker, C. rubidis
- Weyns's duiker, C. weynsi
- White-bellied duiker, C. leucogaster
- White-legged duiker C. crusalbum
- Yellow-backed duiker, C. silvicultor
- Zebra duiker, C. zebra
- Genus Philantomba
- Genus Sylvicapra
- Common duiker, S. grimmia
- Genus Cephalophus
- Subfamily Cephalophinae
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- Colyn, M. et al. 2010: Discovery of a new duiker species (Bovidae: Cephalophinae) from the Dahomey Gap, West Africa. Zootaxa, 2637: 1-30. Preview
|Wikispecies has information related to: Cephalophinae|
|Wikisource has the text of the 1911 Encyclopædia Britannica article Duiker.|
- The African Wildlife Foundation
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