What are the trophic levels in an energy flow system through an ecosystem? What is Lindeman’s Theory?
Elton (1927) suggested constructing a pyramid of energy to have an idea of ecological productivity. The energy pyramid is constructed, thus, on the basis of the total amount of energy used at each trophic level per unit area per unit of time.
The total amount of energy used is generally expressed in kilocalories (Kcal) per square meter per day or per year (Kcal/m²/year).
Energy pyramids help in the comparative study of the productivity of different ecosystems.
Energy Flow Through an Ecosystem
The ecosystem relies on solar radiation as its fundamental source of energy. As this solar energy moves through the food chain and food web, it traverses various trophic levels until it is ultimately expelled from the ecosystem due to energy loss through respiration at each level.
About Biosynthesis and Biodegradation
Biosynthesis is the process of the formation of organic tissue which represents the transformation of solar or light energy into chemical or food energy.
The breakdown and decomposition of organic matter is known as biodegradation. This process involves the release of nutrients and chemical energy in the form of heat, which can be utilized as food. The energy flow (transfer of organic molecules) in the ecosystem is unidirectional and is non-cyclic (is not available again for reuse).
There are 4 Trophic Levels in energy flow.
- Trophic Level 1 belongs to Primary Producers or Autotrophs
- Trophic Level 2 belongs to Herbivores
- Trophic Level 3 belongs to Carnivorous
- Trophic Level 4 belongs to Omnivores
Green plants, also known as primary producers or autotrophs, capture radiant solar energy or sunlight to create food in the form of organic matter through the process of photosynthesis. This conversion of solar energy into chemical energy enables autotrophic or phototrophic green plants to develop their tissues, and the stored energy is held within the primary producers at the base of the trophic levels.
The chemical energy stored at trophic level 1 becomes the source of energy either directly or indirectly to all of the animals at different trophic levels in a food chain in a natural ecosystem. As energy moves from trophic level 1, a portion of it is lost due to respiration, while the remaining chemical energy is transferred to herbivores, which belong to trophic level 2.
Some portion of plants falls down without being consumed by herbivores of trophic level 2 on the ground surface and is ultimately consumed by detrivores or decomposers and thus some energy is also transferred from trophic level 1 to the decomposers living in the soils.
It may be pointed out that the transfer of energy from trophic level 1 (green plants, primary producers, or autotrophs) is performed through the intake of organic tissues (which contain potential chemical energy) of green plants by the herbivorous animals (when a cow grazes grasses, the chemical energy stored in grasses is transferred to the cow).
Thus the chemical energy consumed by herbivorous animals (derived from trophic level 1 through food intake) helps in the building of their own tissues at trophic level 2 and thus the energy is stored in them. This stored energy in the bodies of herbivores now becomes the source of energy for carnivorous animals (secondary consumers) at trophic level 3.
A substantial portion of chemical energy is lost through respiration from herbivores at trophic level 2 because the animals have to consume energy for their movement for getting food from green plants. To perform work, energy is necessary, and when work is done, energy is released in a dissipated form. This occurs when one type of energy is converted into another form, which is governed by the second law of thermodynamics.
At trophic level 3, carnivorous animals receive a portion of potential chemical energy through the consumption of herbivores. Meanwhile, some energy is lost by herbivores through waste products, such as dung and urine, which are decomposed by detrivores or decomposers. When herbivores die, decomposers break down their remains, allowing for the release of the remaining stored energy.
A substantial portion of potential chemical energy stored in the bodies of carnivores is lost through respiration from trophic level 3 because the carnivorous animals have to run for greater distances to catch their prey. A portion of chemical energy is transferred to trophic level 4 or trophic level represented by omnivores (those animals which eat both plants and animals, man is the most important example of omnivores). The animals at trophic level 4. mainly humans also take energy from trophic levels 1 and 2. Again some portion of the energy is released through respiration from trophic level 4 by omnivores. The omnivores, after their death, are decomposed by the decomposers.
Thus it is obvious from the above discussion that there are three-way. pathways of the flow of energy in the natural ecosystem as follows:
- Transfer of chemical energy from each trophic level to the next higher trophic level (i.e. from trophic level 1 to 2, from 2 to 3, and from 3 to 4) and direct transfer of chemical energy from trophic levels 1 and 2 to trophic level 4 (top trophic level);
- Transfer of chemical energy from dead organisms of each trophic level to decomposers, and
- Loss of energy in the form of heat through respiration from each trophic level and from decomposers. All of the heat energy released by organisms through respiration is lost to the atmosphere and cannot be reused by those organisms. As a result, energy flow in the ecosystem is unidirectional and non-cyclic.
First Law of Thermodynamics
The first law of thermodynamics states that energy cannot be created or destroyed in a constant mass system, but it can be converted from one type to another and that the energy inflow or input in a system is equal to the energy outflow or output. This principle is applicable to the energy flow in the ecosystem as described earlier, where solar radiation is converted by autotrophic green plants through photosynthesis into chemical energy or food energy.
The chemical energy is released as heat energy through respiration by the organisms at different trophic levels R.L. Lindeman (1942) has formulated the following five principles regarding the relationships between different trophic levels and energy flow in a natural ecosystem.
Principle I: As the distance between the organisms of a given trophic level and the initial source of energy (trophic level 1) increases, the probability of the organisms depending exclusively on the preceding trophic level for energy decreases. In other words, the organisms at trophic levels 3 and 4 do not depend for their energy only on trophic levels 2 and 3 respectively rather they receive energy from more than one source (trophic level) which means that organisms at trophic level 3 and beyond tend to be ‘generalists’ rather than ‘specialists’ in terms of their feeding habit.
Principle II: The relative loss of energy due to respiration is progressively greater from higher trophic levels because the species at higher trophic levels being relatively larger in Size have to move and work more for getting food and therefore more energy is lost due to respiration.
Principle III: Species at progressively higher trophic levels appear to be progressively more efficient in using their available food supply, because increased activity by predators increases their chances of encountering suitable prey species, and in general predators are less specific than their prey in food preferences.
Principle IV: ‘Higher trophic levels tend to be less discrete than the lower ones’ because the organisms at progressively higher trophic levels receive energy from more than one source (trophic level) and are generalists’ in their feeding habit and they are more efficient in using their available food supply.
Principle V: ‘Food chains tend to be reasonably short. Four vertical links are a Common maximum’ because the loss of energy is progressively higher for higher trophic levels and species at higher levels tend to be less discrete.
Article Written By: Priti Raj