Why are there losses of biomass and energy as we move up trophic levels?
Pyramids of biomass and energy show a reduction with movement up the trophic levels. Biomass is approximately proportional to energy because the biomass is predominantly organic material (with some inorganic material such as ions) so this discussion considers the two interchangeably The reason that not all energy (or biomass) at a lower trophic level is passed to a higher trophic level is because the energy is lost to: • heat generated by respiration • not all of the biomass consumed can be used by the consumer – some material is indigestible and passes out of faeces Of these two the energy lost to heat in respiration is truly lost to the ecosystem. Some of the energy contained in indigestible material will be consumed by decomposers and returned to the ecosystem (Don’t forget that the decomposers also respire and some of the energy they consume is lost as heat) In general only 10% of the energy consumed at a particular trophic level is available to the next trophic level – the rest is
