<P> The trophic level of a species may vary, if it has a choice of diet . Virtually all plants and phytoplankton are purely phototrophic and are at exactly level 1.0 . Many worms are at around 2.1; insects 2.2; jellyfish 3.0; birds 3.6 . A 2013 study estimates the average trophic level of human beings at 2.21, similar to pigs or anchovies . This is only an average, and plainly both modern and ancient human eating habits are complex and vary greatly . For example, a traditional Eskimo living on a diet consisting primarily of seals would have a trophic level of nearly 5 . </P> <P> In general, each trophic level relates to the one below it by absorbing some of the energy it consumes, and in this way can be regarded as resting on, or supported by, the next lower trophic level . Food chains can be diagrammed to illustrate the amount of energy that moves from one feeding level to the next in a food chain . This is called an energy pyramid . The energy transferred between levels can also be thought of as approximating to a transfer in biomass, so energy pyramids can also be viewed as biomass pyramids, picturing the amount of biomass that results at higher levels from biomass consumed at lower levels . However, when primary producers grow rapidly and are consumed rapidly, the biomass at any one moment may be low; for example, phytoplankton (producer) biomass can be low compared to the zooplankton (consumer) biomass in the same area of ocean . </P> <P> The efficiency with which energy or biomass is transferred from one trophic level to the next is called the ecological efficiency . Consumers at each level convert on average only about 10% of the chemical energy in their food to their own organic tissue (the ten - percent law). For this reason, food chains rarely extend for more than 5 or 6 levels . At the lowest trophic level (the bottom of the food chain), plants convert about 1% of the sunlight they receive into chemical energy . It follows from this that the total energy originally present in the incident sunlight that is finally embodied in a tertiary consumer is about 0.001% </P> <P> Both the number of trophic levels and the complexity of relationships between them evolve as life diversifies through time, the exception being intermittent mass extinction events . </P>

Average number of trophic level in the food chain of an ecosystem are