Question

Consider the following food chains:

1. Plants-------> mice------->snakes------->hawks
2. Plants------->mice------->hawks

If energy available at the producer level in both the food chain is 100 J, in which case will hawks get more energy and by how much? Justify your answer.

Answer 1

Ten percent law:

1. Ten percent law states that only 10% of the total available energy is transferred from one trophic level to another.
2. The rest 90% amount of energy is used up or lost to the surroundings.
3. It was proposed by Lindeman in 1942.
4. The energy released at different trophic levels is lost to the surroundings in the form of heat or respiration.
5. So the amount of energy available for the next trophic level is less than the previous level.
6. From various experimental studies, it has been concluded that the energy available for each trophic level is 10% of the previous level.

i. So in the above food chains, hawks will get more energy in the second example because there are only 3 trophic levels which mean energy is reduced by 10% only 2 times.

-10% -10%

Plants----------->mice------------->hawks

100 J 10 J 1 J

ii. In the first example, there are 4 trophic levels which lead to energy being reduced by 10% in each of these levels.

-10% -10% -10%

Plants-------------> mice------------>snakes----------->hawks

100 J 10 J 1 J 0.1 J