Ecological Pyramids: Numbers, Biomass & Energy

Ecosystem

Pyramid Type

Trophic transfer efficiency 10%

Producer turnover rate ×1.0

Upright pyramid

Level Values (current type)

Producers–

Primary consumers–

Secondary consumers–

Tertiary consumers–

Ecological efficiency

–

Top:base ratio

–

How it works

An ecosystem has three classic pyramids, all built from the same four trophic levels (producers → primary → secondary → tertiary consumers), but they measure different things and don't always agree in shape:

Energy flow:     E(n) = E(0) · η^n            (η = trophic transfer efficiency, ~10%)
Standing biomass: B(n) = P(n) / T(n)           (production ÷ turnover rate)
Numbers:          N(n) = B(n) / M(n)           (biomass ÷ average body mass)

The energy pyramid is always upright — each transfer loses energy as metabolic heat (2nd law of thermodynamics), so E(n) strictly decreases. The biomass and numbers pyramids can invert because they depend on turnover rate and body size, not just energy flow:

Ocean plankton: phytoplankton are consumed and regrow so fast (high T) that their standing biomass is lower than the zooplankton grazing on them — an inverted biomass pyramid, even though energy flow still decreases normally.
Forest canopy: a handful of large, slow-turnover trees (huge M, tiny N) support an enormous population of small-bodied insects — an inverted pyramid of numbers.
Parasite chain: each level up is smaller-bodied and faster-reproducing than the host below it, so numbers climb sharply from host to parasite to hyperparasite — a fully inverted numbers pyramid.
Producer turnover slider — scales how fast the producer level's standing biomass replaces itself; push it up and watch the ocean preset's biomass pyramid invert further, or pull it down toward the grassland preset's slow-turnover values and watch the inversion disappear.

This is the real reason biology textbooks stress "energy pyramids are never inverted" while showing counter-examples for biomass and numbers — it's a consequence of turnover rate and body-size scaling, not a violation of energy conservation.

Prairie grass → grasshoppers → shrews → owls

Producers Primary consumers Secondary consumers Tertiary consumers

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