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-ice that continued well into the 20th century. By 1900 at the latest and
probably much earlier, the animal had become feral. The ass became less
popular throughout the world in the early 20th century as the internal combustion engine superseded previous modes of transport and a steep decline in its number in Sri Lanka followed.
Distribution
As a wild species,
Equus africanus occurred in Africa from Morocco to Somalia and in neighbouring parts of the Middle East. It may indeed have evolved in Asia and subsequently moved into Africa. One of the reasons for its remarkable success and wide distribution is its ability to keep its legs in a lock position without muscular contraction, which substantially reduces the energetic costs of feeding, resting, and scanning for predators. In Sri Lanka, the ass is restricted mostly to the northwestern coastal areas, between Puttalam and Jaffna. The soil along the coast is poor and supports a littoral vegetation of halophytic grasses and low scrub. The scrub vegetation includes
Cassia tora, Tephrosia sp. (Leguminosae),
Pentatropis microphylla (Asclepiadaceae), Pedalium nurex (Pedaliaceae)
and salt-tolerant grasses (Poaceae). The growth of grass and its timing, controlled by the onset of rain, may determine the range and distribution of the wild ass in the region. There are also extensive coconut plantations, especially in Kalpitiya where the ass is being kept primarily for release into coconut plantations, on the belief that its braying may drive away the coconut beetles, which are a serious pest of the coconut palm. An alternative local view is that its dung attracts the beetles away from the developing coconut trees.
Ecology
The social organization of the wild ass is virtually identical to that of the Grevy’s zebra
(Equus grevyi). The basic social unit is a mare with her offspring, numbering one or two, and even though these units often combine, they are unstable in the absence of established hierarchies. There are no permanent bonds between any two or more adults. They are found solitary or in a variety of different associations: families consisting of one male, one or more females and their young, bachelor groups, mare groups, groups of mares and foals, solitary stallions, mixed groups, and occasionally, families containing more than one male. All these groups are variable, and their composition may change even within hours. In equids, groups are composed of non-relatives. The biggest family group observed in Kalpitiya comprised 9 individuals.
The sex ratio among adult males and females is roughly 1:0.99, indicating an almost equal mean longevity in the two sexes. There are no natural predators for the asses living in Sri Lanka, but road accidents are a prominent cause of mortality. Given the absence of natural predators, the average group size tends to remain small throughout the year. A small group size is also an advantage for the ass inhabiting marginal habitats of poor productivity. Asses forage as generalists spending a large proportion of their time (60-80%) feeding. The high consumption of forage might be expected to make the asses potent as a cause of overgrazing, but there is no obvious indication of them causing overgrazing where they occur in Sri Lanka. Asses are well known for their capacity to withstand severe dehydration and rapid rehydration. Their hindgut has a role similar to that played by the rumen in goats and camels, serving as water reservoir that under severe stressful conditions, helps maintain the osmotic stability of the body. About 80% of the gut water content of a fully hydrated animal is retained in the hindgut and when the animal is denied water for four days, it will lose 24-30% of its body water, half of which is contributed by the gut.
Bachelor groups range in size from 2 to 11 individuals. Dominance is either inconspicuous or absent, except among territorial males. Asses have specific home ranges within which there are certain cases of partially exclusive male territories, in which a stallion will tolerate conspecifics including certain other males, provided there are no females present. However, a stallion will not tolerate other subordinate males when an estrous female is present. In asses, the dominant males defend territories which confer mating rights over the estrous females. Non-territorial males may aggregate in bachelor groups of up to 11 animals. Mating occurs throughout the year. Male courtship tends to be rather violent, given the intense competition there is for an estrous female from non-territorial males. A stallion may chase an estrous female, pursued by 3-4 other males competing for access to her. The males chase and attempt to bite her. She in turn will lash out at them with one or both her hind feet. The pre-copulatory chase may last up to 10 minutes, during which the parties could be seen running in circles. But if the female is stressed too much, her reproductive performance could be impaired. The dominant male will bray loudly and shriek and squeak in order to intimidate the other males. When mating opportunities are spread out more equitably, even the most subordinate but persistent male is likely to reproduce given that even the most active and dominant male can win only a very few limited number of females. There appears to be no seasonality in the pattern of reproduction of the ass since females give birth all through the year: Although females can breed annually, they usually skip a year because of the strains of rearing foals. The gestation period of 340 days is about 20% longer than that of similarly sized ruminants. The long gestation period ensures that the foals are born in an advanced stage of development. Furthermore, foals can grow quickly if they receive adequate milk from their mothers. Foals are known to double their birth weights in a month. Usually a single foal is born. Asses on average appear to have a total mean life expectancy of about 17 years.
As far as can be judged by external appearance alone, the systematic status of the Sri Lankan population of the ass is that of a rare breed with close affinities with the wild Nubian subspecies, or perhaps even it has a genotype which has been extremely little changed by domestication. A possible cause of such a situation lies in the fact of the trade route from Egyptian ports on the Red Sea to the west coast of India and Sri Lanka having been among the most firmly established and heavily used of the Ancient World. Sri Lanka and southwest India were thus ideally placed to receive imported animals originating from Nubia. There is no a priori reason for ruling out the domestication of
E. africanus via this route separately from other domestic forms of the species. Perhaps the consequent genetic changes have in fact been slight. This is a hypothesis that is best studied by making genetic profiles of the Sri Lankan population and of currently wild individuals. The IUCN (1994) classifies
Equus africanus as endangered as a wild species. The ass needs to be conserved in its habitat.
While it is impossible to determine the total ass population in Sri Lanka, it is clear that their numbers can now be measured in 'hundreds' whereas in the last century, it would have been estimated in 'thousands'. Today although the ass has become a conspicuous member of the local fauna in northwestern Sri Lanka, it is not protected. In the few areas where it survives, it is treated as a nuisance. Capture of animals is pursued aggressively to reduce the number of asses in Mannar and Kalpitiya, where as an animal living wild, it has long been a naturalized species well integrated into the coastal ecosystem and an important part of the island's biodiversity. As such it merits protection. The populations remaining in Mannar and Kalpitiya face continued loss of genetic diversity through isolation and being confined to increasingly smaller areas, and ultimately the threat of extinction as a result of competition with people and their domestic stock for space, water and grazing. Being 'pseudo-ruminants' or simple-stomached herbivores, they are extremely dependent on grazing for food, and thus inexpensive for farmers to feed. Although the abundance of native plants and wildlife tends to be low in areas where they are abundant, it appears that their dietary overlap with domestic bovids is minimal. But the pressure on land continues to increase along the coastal areas of northeastern Sri Lanka as a result of indiscriminate development of prawn farms and resettlement of thousands of refugees made homeless by the civil conflict in the north and east of the island. Asses are excellent draft animals that could be used in rural transportation, given the high cost of the fossil fuels, and the attendant problems of environmental pollution. Reference
to the above material from:
©
Rajnish Vandercone1, T.M. Sajithran2,
S. Wijeyamohan2 and Charles Santiapillai1 (2004)
1
Department of Zoology, University of Peradeniya, Sri
Lanka
2
Department
of Biological Science, Vavuniya Campus of the University of
Jaffna,
Sri
Lanka
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