Production Efficiency

∞ generated and posted on 2016.12.04 ∞

Measure of the amount of biomass stored by consumers relative to the amount of food they successfully absorbed.

Production in Production Efficiency is the storage of biomass and efficiency is that fraction of biomass consumed that actually ends up being stored, i.e., stored as an organism's body, minus that amount lost as feces.

This is secondary productivity, particularly net secondary productivity, or NSP (as analogous to net primary productivity, or NPP). It is what chemical energy is retained by consumers of that which had been successfully taken into their body tissues.

In particular, production efficiency is food consumed minus that energy that is lost in feces (where food consumed minus that lost in feces is equal to gross secondary productivity, or GSP, as analogous to gross primary productivity, or GPP). Subtracted from this gross secondary productivity then is that amount of energy that is lost to metabolism, all as divided by gross secondary productivity (and then multiplied by 100 to make it a percentage).

Note that the energy found in feces is subtracted off because production efficiency is a measure especially of the impact of consumer metabolism on the secondary productivity of ecosystems and that energy found in feces technically has not been lost from an ecosystem since it can be consumed by other organisms, i.e., decomposers.

Whereas production efficiency excludes losses within feces, trophic efficiency, by contrast, takes into account energy losses as found in feces. This is because while one is a measure of ecosystem-wide transfer of biomass between trophic levels (production efficiency), the other (trophic efficiency) is a measure of the efficiency of movement particularly up trophic levels, such as from secondary consumers to tertiary consumers.

Because of this difference, production efficiencies,

     (food - feces - metabolism) / (food - feces) = NSP / GSP

are always greater than trophic efficiencies,

     (food - feces - metabolism) / food = NSP / food.

All calculations are done in energy units (e.g., joules and the energy in the food that an organism consumes is always greater than the organism's gross secondary productivity (GSP). Thus,

     NSP / GSP < NSP / food


     1/GSP > 1/food


     food > GSP

That is, the energy in food eaten is always greater than the amount of food that is assimilated by an organism and therefore production efficiency is always greater than trophic efficiency.

See more generally the concept(s) of ecological efficiency.