Question

Alien species invasion leads to extinction of indigenous species – Justify the statement by considering two animals as examples.

Answer 1

Hint:-The species from another geographic region that have been introduced to an area outside its natural range are called alien species or exotic species. When alien species are introduced into a new habitat, they turn invasive and try to establish themselves.

Complete solution:
There is increased competition for natural resources like food, water, and shelter. All this occurs at the cost of indigenous species also called endemic species (organisms that occur in the particular region naturally). According to the theory of natural selection and survival of the fittest, increased competition and gradual decline in the population of endemic species lead to the gradual extinction of the indigenous species. There are several causes of extinction ranging from habitat destruction to climate change, the introduction of invasive species is also one of the prime reason
(i) Parthenium, Lantana, and Eicchornia are exotic plant species which were introduced in India because of their beautiful flowers and leaves, have now invaded the native species of India, and caused high levels of environmental damage as the species have to compete for food and dissolved oxygen.
(ii) Introduction of African catfish Clarias gariepinus illegally (for aquaculture purpose) is a threat to many indigenous catfish as the African catfish fed on indigenous catfish but the natural predator of African catfish is absent in the region.
(iii) Nile perch introduced into Lake Victoria in Africa led to the extinction of around 200 species of cichlid fish in the lake as Nile perch continuously fed on cichlid fish and no predator of Nile perch was present in the region to keep the Nile perch population under control.

Note:- Natural selection is the differential survival and reproduction of individuals due to differences in phenotype and traits. It is a key mechanism of evolution, the change in the heritable advantageous traits characteristic of a population over generations.