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Wednesday, December 22, 2010

Exotic species and Introduced biodiversity

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Many species of plants and animals are deliberately or accidentally transported by human beings to new locations like islands, countries or regions where they have never inhabited under natural conditions. Disease causing organisms, weeds (like Parthenium or congress grass, Lantana camara and Eupatorium shrubs); insects, pests and rats are introduced to new locations where they form the introduced biodiversity. Species of plants and animals introduced in a country from some foreign land are called as exotic species. These species of plants and animals are potential threats to the lives of indigenous varieties of plants and serious hazards to local biodiversity.

The examples of some most talked about exotic weeds and their impacts in the new habitats are mentioned below –
(i). Lake Victoria is the largest lake of Africa. The introduction of the Nile perch in this lake has driven about 50 per cent of the 400 original species of fish of the lake towards extinction.
(ii).Eucalyptus and Casuarinas are plants of families Myrtaceae and Casurinaceae respectively. These plants are abundantly seen here and there in India but these are of foreign origin. Eucalyptus has been introduced in the Indian sub-continent from Australia and Tropical Americas where as Casuarina has been introduced here from the Southern Hemisphere especially Australia. Though these plants have acquired their places in the country as sources of rough timber their presence is a potential threat to the local species of plants.


Image 1 :  Eucalyptus has been introduced in the Indian sub-continent 
from Australia and Tropical Americas 

(iii). A number of exotic weeds have been transferred form one country to the other country. Parthenium hysterophorus (Congress grass), Agrostemma githago (Corn cockle), Eichornia crassipes, Alternanthera philexeroides (Alligator weed), Salvinia molesta etc. are names of some common weeds of the world that were brought to India along with other materials and were introduced on the Indian land along with seeds of crop plants. These weeds are causing hazardous conditions for the Indian native plants and have already driven away to extinction, many of the Indian plant species besides causing great losses to agriculture.


Image 2 :  Eichornia 
Key words : exotic species, introduced biodiversity, parthenium.



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