Answer:
This is because the level of energy decreases throughout the food pyramid.
At the beginning with producers, they contain the most energy or 100%. However, once they are consumed, the consumer loses 90% of the energy. Thus, primary consumers only get 10% of the energy, secondary consumers only get 1% and so on and so forth higher.
Because of the lack of energy being passed along within the food pyramid, higher order consumers (typically carnivores) must have a lot of prey to consume, but this also means competition. Therefore, higher in the ranks, there is more competition which leads to smaller populations.
