Means of visualizing trophic efficiency.
Pyramids of productivity are built start at the base of food webs, that is, with primary producers. The idea is to provide a picture of the losses going from trophic level to trophic level.
Assuming a trophic efficiency of 10% at each step, then 10,000 units of chemical energy captured via photosynthesis will, if fully consumed, produce at most approximately 1000 units of herbivore body mass. That 1000 units of herbivore body mass will support at most the production of 100 units of carnivore, which in turn will support at most the production of 10 units tertiary consumers (carnivores that specialize on carnivores).
The pyramid of productivity thus would start with a base of 10,000 units wide. On top of that base would be a second tier that is 1000 units wide. The third tier would be 100 units wide, the fourth 10 units wide, and the fifth only a single unit wide. Note that food chains this long tend to be found particularly in the sea, where primary producers are tiny, e.g., single-celled algae and cyanobacteria.
One reason that just aren't all that many top predators in the world is that, due to trophic inefficiencies, it can take a huge amount of primary productivity to support one of these animals. See also biomass pyramid and pyramid of numbers.
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