Energy Losses between Consumers

When a consumer eats, only a small part of the energy in its food ends up in its own body tissues, where it is available to the next trophic level. Typically only around 10% is transferred between consumer levels. Energy is lost in several ways:- Not all of the organism is eaten: roots, bones, fur and shells are often left, and pass to decomposers.
- Not all food is digested: indigestible material is lost in faeces (egestion). Herbivores lose a large fraction this way because they cannot digest much of the cellulose in plant cell walls.
- Excretion: some energy is lost in urine as urea, and in methane from the gut of cattle.
- Respiration: much of the absorbed energy is used in respiration to release energy for movement, active transport and other processes, and is eventually lost as heat.Mammals and birds are endotherms: they keep a constant body temperature, which uses a great deal of energy from respiration. So they transfer a smaller proportion of their food energy into new tissue than ectotherms such as fish and insects.Carnivores digest their protein-rich food more completely than herbivores, so they lose less in faeces.Worked example: a cow eats grass containing 100 000 kJ. 60 000 kJ is egested in faeces, 4000 kJ is lost in urine and methane, and 32 000 kJ is used in respiration.energy in new tissue = 100 000 − (60 000 + 4000 + 32 000) = 4000 kJSo the efficiency of transfer into the cow's tissue is 4000 ÷ 100 000 × 100 = 4%.