ENDEMICITY

        Endemism is a term used in ecology to describe the propensity of plants and animals to be naturally confined to a given geographical area. Plants and animals restricted to such an area are therefore said to be “endemic” to that area. (The term "endemism" is derived from medical science, where a disease is described as endemic if it is confined to a certain area, and epidemic, if it is widespread). Today, the term is mainly used to describe species, and also subspecies, genera or other levels of classification.

Categories of Endemicity


Point Endemics
They are grown only in a particular area and they should be conserved for their restricted distribution.

Biotopes
Species restricted to combination of especial geographic, physical and climatic area. E.g. Quercus durata plant that grows only in Serpentine soil.

Endemics in Biogeographical Regions
Biogeographical regions are large land masses. Endemics in these are associated with climate, soil etc. Therefore they are more natural than endemics in a political area.  E.g. Indo Malayan region, South Asia, etc.

Endemics in political areas
Species defined to a political area. EASL - endemics of Sri Lanka. Most commonly used term to introduce endemic flora or fauna.


Basically endemism is the result of the combination of evolution and geographical isolation. When a population of plants or animals becomes isolated for a long period of time from other populations of the same species, it will diverge as it evolves separately, and eventually form a separate species. The process can also backfire, leading to the extinction of the species population.

Endemism may also occur when a formerly continuous habitat is disrupted by climatic or geological events. Land upheavals may divide a single river system in two, or a change to a more arid climate may cause forests to shrink, dividing once continuous cover into a series of isolated patches.

Endemism is maintained by geographic, physical or climatic barriers to dispersal of the species concerned. The effectiveness of such barriers depends on the particular species, its behavior, its ability to disperse and the nature of its physiology. These barriers represent areas ofunfavorable habitat which individuals cannot easily cross. Most endemic plants or animals are especially adapted to inhabit a significant micro habitat. Dry lands are barriers to aquatic species and species of moist forests, while the medium of water poses a barrier to most land animals and plants.

 Geographical scales of endemism vary across a wide range. An organism may be endemic to a single mountain top, to a mountain range, to a lake, a river system, an island, a country, or even a continent.

Areas with high endemism i.e. having large numbers of endemic species, are of great importance in conservation. Loss of such areas will lead to the extinction of a significant number of species.

endemism is not as permanent as the geographic range of animals and plants and it usually changes over time. Generally, the longer an area has been isolated from other similar areas, the higher the proportion of species which are endemic.over time. Generally, the longer an area has been isolated from other similar areas, the higher the proportion of species which are endemic.

Sri Lanka is a continental island situated near the southern tip of the Indian peninsula, lying between altitudes 5.94’ N – 9.52’N and latitudes 79 39’ E – 81 53’E. It has an overall land area of 6,570,134 ha, but there are almost 10,000 man-made irrigation reservoirs or tanks, especially in the northern half of the island. There are three peneplains, from sea level to 2,600 m.  Of the 103 rivers which start from the central hills, nine are perennial. The combined length of all the rivers amounts to 4560 km.

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