Consider the following statements concerning food chains: (i) Removal of 80% tigers from an area resulted in greatly increased growth of vegetation (ii) Removal of most of the carnivores resulted in an increased population of deer (iii) The length of food chains is generally limited to 3-4 trophic levels due to energy loss (iv) The length of food chains may vary from 2 to 8 trophic levels Which two of the above statements are correct?
- (iii), (iv)
- (ii), (iii)
- (i), (iv)
- (i), (ii)
Answer
(1) (iii), (iv)
Solution
⇒ As per NCERT, only about 10 per cent of the energy is transferred to each trophic level from the lower trophic level (10 per cent law); since energy is lost at every step, food chains are generally limited to 3–4 trophic levels — statement (iii) is correct.
⇒ The number of trophic levels is not fixed: food chains in nature vary in length, from short chains of 2 levels (grass → deer) up to long chains of several links (about 8 at most) — statement (iv) is correct.
⇒ Removal of tigers (top carnivores) allows the herbivores to multiply, and the increased grazing reduces the vegetation instead of increasing it — statement (i) is incorrect.
⇒ Statements (i) and (ii) only describe particular effects of removing predators (a herbivore population also depends on food supply, disease and the other predators present), whereas (iii) and (iv) are the general statements about food chains.
∴ Statements (iii) and (iv) are correct.
Answer: (1)