Only a small proportion of the energy at one trophic level is transferred to the biomass of the next. Between consumer levels the efficiency is often around 10%, although it varies widely.Energy is lost at each transfer because:• not all of the organism is eaten: roots, bones or woody stems may be left, and some organisms die without being eaten (this energy passes to decomposers);
• not all of what is eaten is digested: indigestible material, such as cellulose, is lost in faeces;
• energy is lost in excretion, for example in urea in urine;
• respiration: much of the energy absorbed is used in respiration and is lost to the environment as heat.
The efficiency depends on the type of organism:• Herbivores usually have lower efficiency than carnivores, because plant material contains a lot of cellulose and lignin that is hard to digest, while meat is mostly protein and fat that is easily digested.
• Endotherms (mammals and birds) have lower efficiency than ectotherms (such as insects and fish), because they use a lot of energy keeping warm.Example: Mice and locusts eat grass containing the same amount of energy. The locusts are likely to store more of it as new biomass, because as ectotherms they do not spend energy maintaining a high body temperature.These losses explain why food chains are short and why there is less biomass at higher trophic levels.
• not all of what is eaten is digested: indigestible material, such as cellulose, is lost in faeces;
• energy is lost in excretion, for example in urea in urine;
• respiration: much of the energy absorbed is used in respiration and is lost to the environment as heat.
The efficiency depends on the type of organism:• Herbivores usually have lower efficiency than carnivores, because plant material contains a lot of cellulose and lignin that is hard to digest, while meat is mostly protein and fat that is easily digested.• Endotherms (mammals and birds) have lower efficiency than ectotherms (such as insects and fish), because they use a lot of energy keeping warm.Example: Mice and locusts eat grass containing the same amount of energy. The locusts are likely to store more of it as new biomass, because as ectotherms they do not spend energy maintaining a high body temperature.These losses explain why food chains are short and why there is less biomass at higher trophic levels.