Limits of trophic levels and pyramids

Any calculation of energy, biomass or number must include all the organisms at a trophic level; a few individuals cannot support a generalisation.

A trophic level describes a role, not a species. A single species can work at two or more trophic levels in one ecosystem at once.

Feeding on seeds, fruits and peas, a sparrow acts as a primary consumer; feeding on insects and worms, it acts as a secondary consumer.

Ecological pyramids do not account for a species that belongs to two or more trophic levels.

They assume a simple food chain, which almost never exists in nature, and cannot show a food web.

Saprophytes are left out of ecological pyramids altogether, despite their vital role in the ecosystem.