Question

explain with the help of two examples how the invasion of alien species have disturbed the native species of an ecosystem

Answer 1

The Abingdon tortoise in Galapagos islands became extinct within a decade when goats(alien to that island) were introduced, because goats have better browsing efficiency they survived and tortoise lost the fight for survival.
South American lake visiting flamingoes and resident fishes compete for their common food zooplanktons.
hope it helps.