Energy transfer between trophic levels

A trophic level is a feeding position in a food chain. Energy passes from one trophic level to the next when organisms are eaten, but only part of the energy available at one level reaches the next.

Energy does not all reach the next consumer for several reasons:

• Not all material is eaten. Some organisms are not eaten, and consumers may leave parts of the organisms they eat.
• Not all eaten material is digested. Undigested material is egested, so its energy does not become available to the consumer.
• Organisms respire. Respiration releases energy for life processes, with energy transferred to the surroundings as heat rather than remaining available to the next consumer.

Energy in dead material and waste may pass to decomposers instead of to the next consumer in the food chain.

Energy transfer and food-chain length

Each successive trophic level has less energy available than the level before it. Eventually, too little energy is available to support another consumer level. This is why food chains usually have fewer than five trophic levels.