Unit 2 Lesson 5- Energy Flow in Ecosystem-Trophic Levels, Food Chain & Food Web
Sun is the primary source of energy for all ecosystems on Earth. Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR).
Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis.
Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world. The energy of sunlight fixed in food production by green plants is passed through the ecosystem by food chains and webs from one trophic level to the next. In this way, energy flows through the ecosystem.
The Trophic Structure of Ecosystems
The organisation and pattern of feeding in an ecosystem is known as the trophic structure.=> The levels through which food energy passes from one group of organism to the other group are called trophic levels.
Food Chain
The chain of transformation and transfer of food energy in the ecosystem from one group of organism to another group through a series of steps or levels is called food chain.
Two types of food-chains are recognised:
1. Grazing food-chain: In a grazing food-chain, the first level starts with plants as producers and ends with carnivores as consumers at the last level, with the herbivores being at the intermediate level.
There is a loss of energy at each level which may be through respiration, excretion or decomposition. The levels involved in a food chain range from three to five and energy is lost at each level. The phytoplanktons →zooplanktons →Fish sequence or the grasses →rabbit →Fox sequences are the examples, of grazing food chain.
2. Detritus food chain: This type of food chain goes from dead organic matter into microorganisms and then to organisms feeding on detritus (detrivores) and their predators. Such ecosystems are thus less dependent on direct solar energy. These depend chiefly on the influx of organic matter produced in another system. For example, such type of food chain operates in the decomposing accumulated litter in a temperate forest.
Food WebWhen the feeding relationship in a natural ecosystem become more complicated, the food chain does not remain simple and linear rather it is also complicated by several inter-connected overlapping food chains. This happens when greater number of species feed on many kinds of prey.
Such complicated food chain is called food web.
=> Thus, Energy is passed through the system in food chains and webs. The flow of energy in ecosystems is unidirectional.=> The important point to note is that the amount of energy decreases at successive trophic levels. The
number of trophic levels in the grazing food chain is restricted as the transfer of energy follows 10 per cent law – only 10 per cent of the energy is transferred to each trophic level from the lower trophic level.=> Storage of energy in the system is shown by the amount of living material in both the plants and animals present. The amount of living material present is called the standing crop.=> This can be expressed in several ways but is usually shown as biomass (living material) per unit area, measured as dry weight, ash weight or calorific value.=> Usually the amount of standing crop in each trophic level decreases with each step on the food chain away from the plants. This can be shown diagrammatically by Ecological pyramids.
Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis.
Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world. The energy of sunlight fixed in food production by green plants is passed through the ecosystem by food chains and webs from one trophic level to the next. In this way, energy flows through the ecosystem.
The Trophic Structure of Ecosystems
The organisation and pattern of feeding in an ecosystem is known as the trophic structure.=> The levels through which food energy passes from one group of organism to the other group are called trophic levels.
Food Chain
The chain of transformation and transfer of food energy in the ecosystem from one group of organism to another group through a series of steps or levels is called food chain.
Two types of food-chains are recognised:
1. Grazing food-chain: In a grazing food-chain, the first level starts with plants as producers and ends with carnivores as consumers at the last level, with the herbivores being at the intermediate level.
There is a loss of energy at each level which may be through respiration, excretion or decomposition. The levels involved in a food chain range from three to five and energy is lost at each level. The phytoplanktons →zooplanktons →Fish sequence or the grasses →rabbit →Fox sequences are the examples, of grazing food chain.
2. Detritus food chain: This type of food chain goes from dead organic matter into microorganisms and then to organisms feeding on detritus (detrivores) and their predators. Such ecosystems are thus less dependent on direct solar energy. These depend chiefly on the influx of organic matter produced in another system. For example, such type of food chain operates in the decomposing accumulated litter in a temperate forest.
Food WebWhen the feeding relationship in a natural ecosystem become more complicated, the food chain does not remain simple and linear rather it is also complicated by several inter-connected overlapping food chains. This happens when greater number of species feed on many kinds of prey.
Such complicated food chain is called food web.
=> Thus, Energy is passed through the system in food chains and webs. The flow of energy in ecosystems is unidirectional.=> The important point to note is that the amount of energy decreases at successive trophic levels. The
number of trophic levels in the grazing food chain is restricted as the transfer of energy follows 10 per cent law – only 10 per cent of the energy is transferred to each trophic level from the lower trophic level.=> Storage of energy in the system is shown by the amount of living material in both the plants and animals present. The amount of living material present is called the standing crop.=> This can be expressed in several ways but is usually shown as biomass (living material) per unit area, measured as dry weight, ash weight or calorific value.=> Usually the amount of standing crop in each trophic level decreases with each step on the food chain away from the plants. This can be shown diagrammatically by Ecological pyramids.
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