Question

Read the sources given and answer any four from the questions given below:

The new species called exotic or alien species, when deliberately introduced into a geographical region pose competition for food, space and predation for the existing species. The new or exotic species may cause disappearance of the native species (already present in the natural environment). Lake Victoria, a shallow freshwater lake in South Africa had an extremely diverse collection of over 300 species of small cichlid fishes till 1954.These small fish occupied different niches, some fed on arthropods, some on plants, some were fish-eaters while others fed on fish eggs and larvae. As a large commercial predatory fish, the Nile perch that grows up to 4 feet was introduced in this lake, it spread quickly, eating away the cichlid fish. By 1986, Nile perch constituted 80% of the total fish and the endemic cichlid species were virtually gone. Nile perch threatened the entire ecosystem of the lake. Similarly introduction of water hyacinth Eichhornia, a floating water weed, from South America, when introduced into lakes, spread quickly, and soon covered the entire lake. It blocked the sunlight and led to reduced oxygen level in water, hence threatening the survival of number of aquatic species in the several tropical countries including India.

1. Which of the following was an alien species in Lake Victoria?
   1. cichlid fish
   2. Eichhornia
   3. Nile perch
   4. arthropods
2. The ecosystem of Lake Victoria was disturbed because
   1. Eichhornia occupied the whole lake
   2. competition between cichlid fish and Nile perch
   3. predation by cichlid fish
   4. predation by Nile perch
3. Which of the following is not true for water hyacinth?
   1. it created havoc in the aquatic system where it was introduced
   2. it spreads fast and covers the whole lake quickly
   3. it is a floating water weed
   4. it was introduced in South America in 1986
4. Native species means
   1. new or alien species introduced
   2. species already present in the environment
   3. predatory species of that region
   4. species having different niches
5. The following change took place in Lake Victoria by 1986
   1. Nile perch population grew to 50%
   2. cichlid population fell to 20%
   3. water weed spread through the entire lake
   4. oxygen content of the lake became very low

Answer 1

1. Nile perch
2. predation by Nile perch
3. it was introduced in South America in 1986
4. species already present in the environment
5. cichlid population fell to 20%