Why is a pyramid of biomass narrower at the top than at the base?

A pyramid of biomass is narrower at the top than at the base because each level of the pyramid represents the amount of biomass at different trophic levels in an ecosystem, with producers at the base and higher trophic levels (such as herbivores and carnivores) above. As energy is transferred from one trophic level to the next, a significant portion is lost as heat due to metabolic processes, resulting in less biomass being available for organisms at higher levels. Consequently, there are fewer organisms and less total biomass as you move up the pyramid, leading to its narrower shape.