Question

Why a much larger fraction of energy flows from detritus food chain than from grazing food chain in terrestrial ecosystem?

Answer 1

Grazing food chain starts with producer then herbivores followed by primary carnivore and secondary carnivore. The energy flow rate is fast but magnitude/amount of energy is low because of various levels of orgaism.

Detritus food chain begins with dead organic matter. When organisms die then their body form a source of energy and raw materials for other organisms. The amount of energy present is high in a dead organism.

Now decomposers feed on them by degrading dead organic matter . The energy flow rate is very slow but amount of energy is high as it doesn't any other organisms in between decomposers and dead organi matter.

Detritivores may be fed up upon by carnivores, thus building a food chain based on detritus.