In an ecosystem, diverse organisms live together and continuously interact with one another by transferring energy and nutrients. One organism is eaten up by another organism allowing the flow of nutrients and energy, forming food chains. Many food chains interact within a single ecosystem and make a food web. A food chain provides a clear-cut idea about the feeding patterns and relationships between diverse organisms living in an ecosystem.
A grazing food chain derives energy from the sun. The photosynthetic green plants utilize solar energy and fix the abiotic carbon dioxide into a biologically available form that is glucose. The producers are eaten up by herbivores which in turn are eaten up by carnivores. The decomposers convert the dead and decaying matter into usable nutrients within the soil to be available for the plants to recycle the nutrients. Thereby the energy flows unidirectionally.
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The grazing food chain depends on solar energy which is its primary energy source.
It adds up the energy to the ecosystem at every trophic level.
It fixes the inorganic nutrients in the atmosphere into biologically accessible forms.
Although the primary energy source is solar energy, the grazing food chain is again of two types.
Predator food chain
The green plants are producers that are eaten up by herbivores which in turn are consumed by carnivores and so on.
The matter and energy flow from small organisms to large organisms.
Parasitic food chain
In a parasitic food chain, the green plants are eaten by large herbivores upon which small parasites inhabit. Otherwise, the green plants themselves are infected by small parasitic insects within which microscopic hyper parasites like bacteria and fungi live.
Energy and matter flow from large organisms to small organisms.
All food chains in an ecosystem do not necessarily start with producers. Detritus food chains start with dead and decaying organic matter. Detritivores are organisms consuming dead and decaying matter and are in turn consumed by small predators that are prey for large predators.
Unlike a grazing food chain, the detritus food chain is small and energy flows from small-sized detritivorous organisms to bigger predators and even large predators. The primary energy source is dead and decaying matter. The detritivores fix the inorganic nutrients of the soil and make it into bioavailable form in the food chain. This implies that energy is taken up from the ecosystem.
All living organisms require energy to carry on the life processes like respiration, locomotion etc. Energy fixation is defined in terms of productivity which is defined as the rate at which living organisms add energy in the form of biomass. Gross productivity is the overall rate of energy fixation.
Within a grazing food chain, the green plants are producers. Some portion of the fixed energy is utilised for carrying on the life processes and some part is transferred to the herbivores that feed on them. Within the herbivores, of all the acquired amount of energy, some portion is utilised for respiration and little is excreted out of their bodies. The available form for the next trophic level is slightly lower than that acquired from the producers. In this manner, moving forward in a food chain, only some portion of the acquired energy is transferred to the next trophic level. Most of the energy is lost through respiration or, excreted out of the body.
Energy transfer within food chains is represented in the form of pyramids. The energy pyramids start with producers at the bottom and each step is one trophic level. As going further from the base to the top of a pyramid, the steps get smaller, depicting that not all energy at a trophic level is transferred to the next level. Only about 10% of the energy stored as biomass is transferred to the next trophic level. This is called the 10% rule in an ecosystem. So as we move along a food chain, the energy transferred between trophic levels gradually falls down. This limits the number of trophic levels each food chain can support.
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Grazing food chain (Predator) in a terrestrial ecosystem −
Grazing food chain (Predator) in an aquatic ecosystem −
Grazing food chain (Parasitic)in a terrestrial ecosystem −
| Feature | Grazing food chain | Detrital food chain |
|---|---|---|
| Energy source | Sunlight | Organic debris |
| Role in an ecosystem | Adds energy to the ecosystem | utilises energy from the ecosystem |
| Constituent organisms | Mostly macroscopic | Microscopic and macroscopic |
| Organisms of first trophic level | Autotrophic green plants | Detritivores |
| Size of food chain | larger | Comparatively smaller |
The grazing food chain starts with photosynthetic organisms and chlorophyll is the main essential pigment to run the entire food chain.
It is equally predominant on land as well as in water.
Inorganic and abiotic components play an important role in energy generation at the first trophic level.
Living organisms require energy to run the life process like respiration, and locomotion. Organisms within an ecosystem are diverse and interact continuously with one another for nutrients and energy. The grazing food chain starts with the autotrophic green plants forming the first trophic level. They depend on sunlight as the energy source and are consumed by herbivores that in turn are consumed by carnivores. The energy and biomass are transferred in a food chain. As we move across the food chain, the amount of energy transferred gradually decreases. Only 10% of the energy is transferred to the next trophic level. Detritus food chains are completely opposite to grazing food chains and derive energy from dead organic matter.
Q1. Name some detritivores?
Ans. Millipedes, earthworms, slugs, dung flies and snails are some detritivores.
Q2. Who proposed the 10% energy transfer rule?
Ans. Reymond Lindenman proposed the 10% energy transfer rule also called the Lindenman trophic efficiency rule.
Q3. What is the role of decomposers in a grazing food chain?
Ans. The dead organic matter is converted to a biologically available form for plants and nutrient recycling is performed by decomposers.
Q4. What is meant by energy pyramid?
Ans. Energy pyramid is the representation of energy flow at each trophic level in a food chain. It gives an idea about the energy transferred and that is lost into the environment at each trophic level within a food chain.
Q5. What information can be drawn from a food chain?
Ans. A food chain gives information about how different organisms interact with one another and the relationship lying between them. Suppose when an organism is lost or is facing a risk of potential loss from an ecosystem it is easily understood by studying the associated food chain.
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