Understanding Energy Flow in Ecological Pyramids

Ecological pyramids visually represent the biomass or bio-productivity at each trophic level in a given ecosystem. They help us understand how energy flows through different levels, from producers to consumers.

Energy Transfer Efficiency and the 10% Law

Energy transfer between successive trophic levels is not 100% efficient. A significant portion of the energy consumed at one level is lost before it can be converted into biomass at the next level. This loss occurs primarily due to:

• Energy used for metabolic activities like respiration, movement, and growth.
• Energy lost as heat to the environment.
• Energy that is not consumed (e.g., parts of plants not eaten by herbivores).
• Energy lost as waste products (e.g., excretion).

Only a small fraction of the energy consumed by an organism is actually stored as new biomass, which then becomes available to the next trophic level. This efficiency is governed by the "10% Law" of energy transfer, first proposed by Raymond Lindeman in 1942.

The 10% Law Explained

The 10% Law states that, on average, only about 10% of the energy from one trophic level is transferred and incorporated into the biomass of organisms at the next trophic level. The remaining 90% of the energy is lost or used up in various life processes, as mentioned above.

For example:

• If producers (plants) have 1000 units of energy, primary consumers (herbivores) that eat these plants will incorporate only about 10% of this energy, i.e., 100 units, into their biomass.
• Secondary consumers (carnivores that eat herbivores) will get only about 10% of the herbivores' energy, i.e., 10 units.
• Tertiary consumers will get only about 10% of the secondary consumers' energy, i.e., 1 unit.

This progressive loss of energy explains why ecological pyramids of energy are always upright (broader at the base) and why there are usually only 4-5 trophic levels in an ecosystem; there isn't enough energy left to support higher levels.

Energy for Building New Biomass

The energy that is successfully transferred to the next trophic level is the energy that is converted into new biomass by the organisms at that level. This new biomass includes the growth of existing organisms and the reproduction of new organisms. Based on the 10% Law, about 10% of the energy consumed from the lower level is used for this purpose.

Therefore, approximately 10% of the energy available at one trophic level is used to build new biomass at the next trophic level in an ecological pyramid.

Conclusion on Energy Transfer in Biomass

The question asks about the percentage of energy used to build new biomass in an ecological pyramid, which directly relates to the efficiency of energy transfer between trophic levels. The widely accepted ecological principle, the 10% Law, states that only about 10% of the energy is transferred and becomes available as biomass at the next level.

Thus, about \(10\%\) energy is used to build new biomass in an ecological pyramid.

Revision Table: Ecological Energy Flow

Additional Information on Energy Pyramids and Biomass

While the 10% law is a useful generalization, the actual energy transfer efficiency can vary depending on the specific ecosystem and trophic levels involved. However, it rarely exceeds 20% and is often much lower. This significant energy loss at each step has profound implications for the structure of ecosystems and the sustainability of food chains.

Pyramids of biomass can sometimes be inverted in certain aquatic ecosystems (e.g., when phytoplankton biomass is less than zooplankton biomass at a specific time), but pyramids of energy are always upright because energy flow is always highest at the producer level and decreases progressively at higher levels.

Understanding energy flow and the 10% law is crucial for studying ecosystem dynamics, productivity, and the impact of human activities on food webs.