Trophic Levels

An energy pyramid stacks trophic levels from the bottom up: producers (plants, algae, cyanobacteria) capture sunlight and turn it into chemical energy through photosynthesis. Primary consumers eat producers, secondary consumers eat primary consumers, and tertiary consumers eat secondary consumers. At every transfer, most of the energy an organism takes in is lost as heat through metabolism, used for movement and growth, or left behind in waste and uneaten parts. Only roughly 10% gets packaged into new body tissue that the next level up can actually eat. This is the 10% rule, and it's why pyramids taper sharply as you climb.

Because so little energy survives each transfer, there isn't enough left after three or four steps to support another level, let alone a pile of big predators. A food chain with producers, primary consumers, secondary consumers, and tertiary consumers already stretches the energy thin; a fifth level would need an enormous base of producers underneath it to make any sense. That's the real reason lions don't stack on zebras the way zebras stack on grass: the energy to build lion bodies has already been cut down by a factor of a thousand.

Pyramids built on numbers or biomass don't always taper the same way energy does, because counting individuals or mass ignores how much energy each one represents. Decomposers complicate the picture further: they feed on dead material from every level at once, so they're sometimes drawn as a separate column running alongside the whole pyramid rather than stacked on top of it, recycling nutrients back to producers instead of passing energy further up.