|Copyright: ronny hole (ronnyho)
|Date Taken: 2014-01-07|
|Camera: Canon 7D, Canon EF400mm f/5.6L USM|
|Exposure: f/5.6, 1/1600 seconds|
|More Photo Info: [view]|
|Photo Version: Original Version|
|Date Submitted: 2014-02-28 2:29|
|[Note Guidelines] Photographer's Note|
|A small group of Zebra's photographed in Selous Game Reseve in Tanzania.|
It was previously believed that zebras were white animals with black stripes, since some zebras have white underbellies. Embryological evidence, however, shows that the animal's background color is black and the white stripes and bellies are additions. It is likely that the stripes are caused by a combination of factors.
The stripes are typically vertical on the head, neck, forequarters, and main body, with horizontal stripes at the rear and on the legs of the animal. The "zebra crossing" is named after the zebra's black and white stripes.
A wide variety of hypotheses have been proposed to account for the evolution of the striking stripes of zebras. The more traditional of these (1 and 2, below) relate to camouflage.
1. The vertical striping may help the zebra hide in grass by disrupting its outline. In addition, even at moderate distances, the striking striping merges to an apparent grey.
2. The stripes may help to confuse predators by motion dazzle—a group of zebras standing or moving close together may appear as one large mass of flickering stripes, making it more difficult for the lion to pick out a target.
3. The stripes may serve as visual cues and identification. Allthough the striping pattern is unique to each individual, it is not known whether zebras can recognize one another by their stripes.
4. Experiments by different researchers indicate that the stripes are effective in attracting fewer flies, including blood-sucking tsetse flies and tabanid horseflies. A 2012 experiment in Hungary showed that zebra-striped models were nearly minimally attractive to tabanid horseflies. These flies are attracted to linearly polarized light, and the study showed that black and white stripes disrupt the attractive pattern. Further, attractiveness increases with stripe width, so the relatively narrow stripes of the three living species of zebras should be unattractive to horseflies.
The Selous Game Reserve is an ecosystem (7,400,000 ha) and includes Mikumi National Park and Kilombero Game Controlled Area. A large area of the reserve is drained by the Rufiji River and tributaries that include the Luwegu, Kilombero, Great Ruaha, Luhombero and Mbarangardu. The Rufiji is formed by the Luwegu and Kilombero which join at Shughuli Falls. Soils are relatively poor and infertile.
While there are many habitat types, the deciduous miombo woodland is dominant, providing the world's best example of this vegetation type; as this is thought to be maintained by fire it may be the result of human activities in the past.
The reserve has a higher density and species diversity than any other miombo woodland area, despite long winter drought and poor soils, owing to its size, the diversity of its habitats, the availability of food and water and the lack of settlements. Animal populations in the surrounding areas are often as high, especially in the dry season and contain many of the same species. Some 400 species of animal are known and in 1986 approximately 750,000 large animals of 57 species were recorded. The greatest concentrations are in the north and north-east, also in the inner south. In 1994, in the reserve and surrounding buffer area, there were 52,000 of the endangered African elephant, 50% of the country's total, which is growing again after years of decline due to ivory poaching: 109,000 in 1980 had dwindled to 31,000 by 1989. Within the reserve they totalled 31,735 in 1994 and are found throughout the area. The critically endangered black rhinoceros, which numbered 3,000 in 1981, are now estimated as between 100 and 400 in several small scattered populations.
Several animal populations are large (the figures are quoted from a 1994 aerial survey by TWCM): buffalo (138,000), blue and nyasa or white-bearded wildebeest (46,500), impala (29,500), Burchell's zebra (21,500), Lichtenstein's hartebeest (20,000), kongoni (11,700) and common waterbuck (10,000). Grassland species north of the Rufiji include giraffe (2,200), blue wildebeest, buffalo, impala, eland, reedbuck, warthog, lion (vulnerable at 3,000-4,000) and an occasional cheetah, also vulnerable. Hippopotamus (27,000) and crocodile are abundant. Greater kudu, sable antelope (1,600), with eland, impala, nyasa wildebeest and hartebeest are typical of the miombo woodland. Other relatively widespread mammals include yellow baboon, leopard, spotted hyena, the largest population of the wild dog in Africa (endangered: approximately 1,300). There are also sidestriped jackal, puku, klipspringer, and red and blue duikers. Rarer species include Sanje crested mangabey, Uhehe red colobus (vulnerable), black and white colobus monkey, topi and Sharpe's greysbok.
The birdlife is rich: 350 species of bird have been recorded including knob-billed duck, southern ground hornbill and bateleur eagle, Stierling's woodpecker, white-headed lapwing, the endemic Udzungwa forest partridge (classed as vulnerable) and the rufous-winged sunbird (also vulnerable). The adjacent Mikumi lowlands and mountains and Kilombero wetlands and the nearby Udzungwa Mountains are rich in vulnerable bird species which, like the Kilombero weaver, might stray into the reserve. The globally threatened wattled crane, corncrake and lesser kestrel also occur. Reptiles and amphibians are numerous but little studied.
The area is so large that it can absorb all but the most severe pressures on its resources. There are plans to harness the flood waters of the Rufiji River, with a dam to be constructed at Stieqler's Gorge; but this would affect only relatively small part of the reserve and should not be a matter of Selous concern unless the reservoir draws in large numbers of settlers. Because of difficulties of transportation, the interior of Selous is seldom patrolled, so the estimated numbers of species may be far in excess of the current true situation if poaching has been as serious a problem as elsewhere in East Africa. Much of the infrastructure of the site (roads, guardposts, water systems, etc.) has deteriorated in recent years due to lack of sufficient funding.
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