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12th Biology 2012 Set1 Outside Delhi Board Paper Solution

Question 26

Alien species are highly invasive and are a threat to indigenous species. Substantiate this statement with any three examples.

When alien species are introduced unintentionally or deliberately, they turn invasive and cause decline or extinction of indigenous species. Three examples are-
(i) Cichlid fish which is found in Lake Victoria led to extinction of nearly 200 species which introduced Nile Perch into Lake Victoria.
(ii) The inclusion of invasive species such as carrot grass (Parthenium), Lantana and water hyacinth (Eicchornia) led to environmental damage of the native species.
(iii) The indigenous catfishes found in rivers are a major species of extinction by the introduction of African catfish Clarias gariepinus which is a major advantage for aquaculture purposes.