5.10—Biomass and energy transfer efficiency

Only part of the energy or biomass entering a trophic level becomes new tissue. Transfer efficiency is useful output divided by input, multiplied by 100; losses include respiration heat, egestion, excretion and uneaten material.

For energy, first subtract losses to find net productivity. For biomass, use dry mass and ensure intake and transferred biomass share units before applying the percentage formula.

A consumer receives 10,000 kJ m⁻² yr⁻¹ and loses 9,000 kJ, so its net productivity is 1,000 kJ and efficiency is 10%. A dry-mass calculation uses the same ratio logic but a different measured input.

The familiar “10% rule” is not a fixed law. Efficiency depends on organism, food quality and conditions; biomass transfer is not the same as counting the wet mass of organisms.