1. When invasive species are accidentally or intentionally introduced into a particular region which causes extinction of local and already existing species, it is called alien species invasion.
2. Examples of such invasive plant species are (a) the carrot grass (Parthenium) (b) Lantana(c) Water hyacinth (Eichhornia).
3. Invasive animal species is African catfish Clarias gariepinus, introduced for aquaculture purpose. This has caused harm to endemic catfish varieties.
4. Invasion by such species is one of the major reasons for extinction of local species.
