The various steps in which the transfer of food or energy takes place are called trophic levels.
The killing of all the organisms in one trophic level will also lead to the overpopulation of organisms in the previous trophic level.
The loss of energy occurs as heat at each step of the trophic level in the environment.
At each trophic level, organisms utilize energy in respiration.
Grass →Insect →Frog→ Bird.
In this food chain, grass represents the 1st trophic level; insects represent the 2nd trophic level; frog represents the 3rd trophic level, whereas birds represent the 4th trophic level.