What are the destinations of the organic material fabricated by the producers?
Net primary production is the gross primary productivity less the organic material consumed as energy source in the metabolism of the producers: NPP = GPP – (organic material spent in aerobic respiration). It represents the organic material available in the first trophic level. The base of the energy pyramids must represent the NPP and not the GPP since the idea of these pyramids is to show the available energy in each trophic level of the food chain.
Part of the organic material synthesized by the producers is consumed as energy source for the metabolism of the own producer individual. The other part is incorporated (into the body) and becomes available to heterotrophic beings of the ecosystem. In each following trophic level part of the organic material is used in the metabolism of the individuals of the level, the other part is eliminated as waste and only a fraction is incorporated and becomes available as food for the following level.
