How efficient is energy transfer between trophic levels?

Energy transfer between trophic levels is typically only about 10% efficient.

In an ecosystem, energy flows from one trophic level to the next, starting with the producers (like plants) and moving up to various levels of consumers (like herbivores and carnivores). However, this energy transfer is not very efficient. On average, only about 10% of the energy at one level is transferred to the next. This is known as the 10% rule in ecology.

The reason for this low efficiency is due to several factors. Firstly, not all of the organism is consumed. For example, bones, scales, fur, and other indigestible parts are often left behind. Secondly, not all of the consumed energy is available for the next trophic level. A significant portion of energy is used for the organism's own metabolic processes, such as respiration, movement, and reproduction. This energy is lost as heat and cannot be used by the next trophic level.

Furthermore, some energy is lost in the form of waste products. For instance, when a rabbit eats a plant, it does not absorb all the energy from the plant material. Some of it is excreted as waste. The energy contained in this waste is not available for the next trophic level, further reducing the efficiency of energy transfer.

This low efficiency of energy transfer has important implications for the structure of ecosystems. It explains why there are usually fewer organisms at higher trophic levels. Each successive level can only support about one-tenth the number of organisms as the level below it. This is why, for example, there are fewer lions than there are zebras in the African savannah, and why there are fewer zebras than there are grass plants. The 10% rule is a fundamental principle in understanding the dynamics and structure of ecosystems.