A measure of the efficiency of energy flow between trophic levels in a food chain. It is the percentage of energy from a trophic level that is used by the organisms of the next trophic level for growth and reproduction. Hence, it does not include energy lost via respiration and faeces, nor material from the previous trophic level that is not consumed. Trophic efficiencies can range from 5% to 20%, depending on the type of ecosystem, with an average of about 10%. This means that considering just three trophic levels, only 1% of net primary production is available to a secondary consumer.