Models of Energy Flow

Core Ontological Distinctions

The Single-Channel Model shows unidirectional energy attenuation along a single grazing food chain. The Y-Shaped (Double-Channel) Model is more realistic because it splits Net Primary Productivity into two simultaneous arms—the Grazing Food Chain and the Detritus Food Chain—which are separated in space/time but cross-linked at carnivore levels. The Universal Model is a standardized single box ($I \rightarrow B \rightarrow P + R$) that can represent an individual, a population, or a whole trophic guild.

Consumption Efficiency ($I_n / P_{n-1}$) is how much of the lower tier is actually eaten. Assimilation Efficiency ($A_n / I_n$) is how much of the eaten food is digested across the gut wall rather than defecated. Net Production Efficiency ($P_n / A_n$) is how much of the digested energy becomes new body biomass rather than being burned as respiratory heat. Multiplying all three gives Lindeman's Trophic Transfer Efficiency ($\text{TLTE} = \text{CE} \times \text{AE} \times \text{NPE} \approx 10\%$).

Carnivores have high Assimilation Efficiency (~80–90%), whereas Herbivores have low AE (~20–50%). However, Endotherms (birds and mammals) have tiny Net Production Efficiency (~1–3%) because ~98% of assimilated energy goes into maintaining constant body heat, whereas cold-blooded Ectotherms (insects, fishes, reptiles) convert 20–50% of assimilated energy directly into new biomass.