Energy flow in an ecosystem | Ecological pyramid

Energy flow in an ecosystem | Ecological pyramid


An ecosystem is a group of many communities and different abiotic factors which influence that community. At this level of ecology, ecologists usually focus on flow of energy and recycling of different nutrients.

What is energy flow in an ecosystem?

In an ecosystem, the energy flow means the amount of energy that passes through a food chain from one trophic level to another.


Energy can be defined as the ability (or the capacity) to do any work. It is measured in joules or calories, thus the energy flow is also called as the calorific flow. Hence the S.I. unit of energy is joule (J). It exists in two different forms, these are:

  • Potential energy
  • Kinetic energy

Potential energy:

The energy at rest is called as the potential energy. Potential energy is also called as the stored energy which is capable of performing work.

Kinetic energy:

The energy of motion or the energy required to perform movement is called as the kinetic energy.

Energy flow in an ecosystem

> The primary or the main source of energy is the radiant energy of sun which gets converted into chemical energy and is then required by all living organisms in their food to meet their energy requirement.

> The radiant energy from the sun is released in the form of electromagnetic waves during the transmutation of hydrogen to helium. 

> The chemical energy which is formed, is then stored in the food of living organisms which is converted into potential energy by the arrangement of the constituent atoms of food in a certain manner.

> Thus, it results in performing a work at the expense of potential energy.

> In an ecosystem, the energy flow is always unidirectional. It can only pass from the lower trophic level to the topmost trophic level through more other trophic levels, but can never flow from the topmost trophic level back to the lower trophic level.

This energy flow is based on two important Laws of Thermodynamics which are stated below:

(1) The first law of Thermodynamics:

The first law of Thermodynamics states that the amount of energy in the universe always remains constant. This energy may change from one form to another, but it can neither be created nor destroyed. Thus, light energy (from the sun) also being a kind of energy can be neither created nor destroyed it may, however, be transformed into another form of energy (such as, chemical energy or heat energy).

(2) The second law of Thermodynamics:

The second law of Thermodynamics states that the energy cannot be changed into another form or transferred without any degradation into heat energy. Thus, the change of energy from one form to another occurs in such a manner that a part of energy is wasted in the form of heat energy. In this manner, after transformation, the amount of energy required to perform a work is gradually decreased. Thus, energy flows from higher energy level to lower energy level.


In an ecosystem energy flows in two different forms, radiant energy and fixed energy. Radiant energy flows in the form of electromagnetic waves, such as light. Whereas, fixed energy is the stored chemical energy bound in various organic substances which can be broken down in order to release their energy content.

Organisms that can absorb radiant energy of the sun and can produce organic substances utilizing it are called autotrophs (or producer in food chain). These autotrophs or producers are actually plants which are capable of making food using sunlight by the process called photosynthesis. Whereas, organisms at immediate next trophic level in the food chain after producer, cannot obtain energy directly from the sun and are dependent on autotrophs to obtain energy are called heterotrophs.

Organisms at successive trophic levels after heterotrophs which obtain energy from other living organisms are called consumers and organisms which obtain energy from dead and decaying organisms are called decomposers (or saprotrophs).

Flow of Energy at different Levels of Ecosystem

In an ecosystem, energy flows from one trophic level to another on the basis of 10 percent law of energy flow which states that when energy passes from one trophic level to another in a food chain, only 10 percent of that energy passes on to the next trophic level.

Initially when the light energy (from sunlight) falls on the green surfaces of the leaf of a plant, 10 percent of this energy is transformed into chemical energy which is stored in various organic products within the plants. When the herbivores (primary consumers) consume plants as their food and convert chemical energy stored in plants into kinetic energy, degradation of energy occurs in the form of heat, only 10 percent of that energy passes on to them.

When herbivores are consumed by primary carnivores (secondary consumers) further degradation of energy occurs in the form of heat, only 10 percent of that energy also passes on to them. Similarly, when the primary carnivores (secondary consumers) are consumed by the top carnivores (tertiary consumers), again more energy will be degraded and 10 percent of that energy passes on to them too.

Ecological pyramid:

An ecological pyramid is a pyramidal-shaped graphical representation of the trophic levels of a food chain of an ecosystem. It shows the relationship between all the different trophic levels of a food chain. Energy flow in an ecosystem is more likely understandable through this ecological pyramid, where the base of the pyramidal representation is usually much broader than that of the other successive steps and is occupied by the lowest trophic level, the producers (which are generally plants).

The base of the pyramid being broader contains large amount of energy and at each successive steps in the pyramid a considerable amount of the potential energy is lost as heat and only 10 percent of that energy passes and similarly in this manner at every steps of a pyramid only 10 percent of the energy of the previous step passes.

Thus, every steps of a pyramidal representation gradually decreases as moves from the base towards the top giving it a pyramidal shape. As a result, the higher the steps of the ecological pyramid, the lower will be the number of individuals in that step.

Also Read

Ecology: Importance and Examples | Biotic and Abiotic factors | Levels of ecology

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