In an ecological pyramid, when you move up, biomass and the number of species, they all decrease as energy is lost when it moves up each trophic level.
Only 10 percent of the energy at any trophic level is transferred to the next level and the remaining energy is lost through metabolic processes in the form of heat. Each trophic level needs enough energy to sustain it, and hence, the competition for resources rises which causes a decrease in the number of organisms.