Answer:
The population decreases as we go from the bottom of the food chain to the top.
This is due to the fact that in most of the ecosystems, producers are far more in number and biomass than herbivores ( its subsequent trophic level), herbivores are more in number than carnivores and so on.
Energy at lower trophic level is always more than at a higher level.
[ As energy flows from a trophic level to another, some amount of energy is lost in the form of heat at each level.]