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Food Web refers to the energy transfer from producers like plants to consumers like animals. It is estimated that around 3.7 million Exajoules of solar energy reach the entire planet. Food Web is a depiction of the myriad transformations and interactions that take place in the transportation of energy. It shows how the energy, when produced and captured, gets transported to different organisms at different levels.
Food webs include several food chains combined together. Each food chain includes a series of arrows pointing from one species to another. The chain represents the flow of food energy from one feeding group of organisms to another. Food webs can be used to illustrate indirect interactions among species. They depict different patterns of energy transfer in terrestrial and aquatic ecosystems.
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Food Web
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Food web basically refers to the flow of energy from the producers to the consumers. It is also defined as the interlinking of food chains at different trophic levels. Compared to the food chain, the food web is more tangible in the ecosystems and it ensures the stability of an ecosystem. The Food web creates stability in the ecosystem by controlling the population levels of the organisms.
Food webs include a number of food chains meshed together. A food chain is a descriptive diagram that represents the flow of food energy from one feeding group of organisms to another. The food web offers an important tool for investigating the ecological interactions that define energy flows and the predator-prey relationship. Most food webs are complex and involve many species with both strong and weak interactions among them.
Food Chain
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A food chain normally depicts the flow of energy in an ecosystem. In a food chain, each organism consumes its predecessor for the need for energy. Normally, the photosynthetic organisms or primary producers are at the start of a food chain and it ends at the top carnivore or apex predator.
The food chain is a hypothetical concept created for understanding the process of energy transfer in an ecosystem. Each level of the food chain is called a trophic level and most of the food chain carries 3-6 trophic levels. The energy, biomass, and number of organisms perpetually decrease when moving along the trophic levels. A considerable amount of energy is lost in the form of heat at each trophic level.
An Example of Food Chain
There are two types of food chains:
- Grazing Food Chain: This food chain begins with autotrophs. In a grazing food chain, energy and nutrients move from plants to the herbivores consuming them. Then they move to the carnivores or omnivores preying upon the herbivores.
- Detrital Food Chain: Detrital food chain begins with dead organic matter. In a detrital food chain, dead organic matter of plants and animals is broken down by decomposers and moves to detritivores and then carnivores.
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Types of Food Chain
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There are two types of food chains, the Grazing Food Chain and the Detrital Food Chain.
Grazing Food Chain
In a Grazing food chain, energy is gained from photosynthesis. This chain starts with producers – plants and the first energy transfer is from plants to herbivores. The received energy is at the lowest trophic level. In an aquatic ecosystem, the grazing food chain plays a key role in the transfer of energy flow. The grazing food chain is further classified into two categories:
- Predator Chain: The sequence of organisms increases in size.
- Parasitic Chain: The sequence of organisms decreases in size.
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Detritus Food Chain
The Detritus food chain is initiated from the dead bodies of organisms. Decomposers and scavengers are the major consumers in this food chain. This food chain is also known as the saprophytic food chain. The organisms feeding on the dead and decaying matter are called detritivores. These are eaten by predators. This chain produces a large amount of energy for the ecosystem. Detritus food chains are found in a various places like the bottom of the ocean, sea, ponds, and also in lakes.
Trophic Level
The trophic level is the division of organisms in a food chain and it is determined by the method used by the organism in obtaining its energy by means of food. Trophic levels in a food chain are equal to the number of divisions present in a food chain. Generally, the trophic level begins from the producers such as plants to the top carnivores such as eagles or owls.
Ten Percent Rule in Food Web
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This law gives an account of the transfer of energy from one trophic level to another. The Ten Percent law states that only ten percent of consumed energy is transferred from one trophic level to the next trophic level. The flow of energy from one level to another determines the number of trophic levels in a food chain. The ten percent law was proposed by Raymond Lindeman.
Energy flows through different trophic levels. It begins with the energy from the sun that is used by autotrophs to produce food. This energy is transferred upwards through different levels as organisms are consumed by members of the levels above them. 10% of the energy that is transferred from one trophic level to the next is converted to biomass. The overall mass of an organism or the mass of all the organisms that exist in a given trophic level.
Types of Trophic Levels in a Food Web
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The different types of trophic levels in a food web are elaborated below:
Primary Producers
Generally, photosynthetic organisms like plants and algae are included in the primary producers. They are able to produce food by themselves by using solar energy. Primary producers are the basic part of an ecosystem. They can be thought of as the first and most important step in the food chain. Along with decomposers, they make up the base of a food web. Primary producers are consumed by primary consumers which are then consumed by secondary consumers. Organisms at the top of the chain are consumed by decomposers that fix the nitrogen levels.
Primary Consumers
Primary consumers are the organisms that obtain their energy by consuming the primary producers. Herbivores are generally regarded as the primary consumers. Primary consumers of the food web are the first organisms to eat the primary producers who make their own food. These animals are also known as herbivores. Examples are rabbits, beavers, elephants, and moose.
Secondary Consumers
Secondary consumers prey on primary consumers for their food. They will either be omnivores or carnivores. They are in turn consumed by the tertiary consumers for their food. Decomposers and detritivores are also essential parts of the food web. The final level of the food web consists of the apex predators. Secondary consumers are generally meat-eaters (carnivores).
Tertiary Consumers
The organisms that eat the secondary consumers are called tertiary consumers. These are carnivore-eating carnivores; such as eagles or big fish. Food chains have additional levels, such as quaternary consumers (carnivores that eat tertiary consumers).
Things to Remember based on Food Web
- Food chain is the flow of energy through organisms present in an ecosystem.
- Food web is the interconnection of different food chains present in an ecosystem.
- Food web is more of a real concept, whereas the food chain is a hypothetical concept.
- Biomass, energy, and the number of individuals gradually decrease moving along the food chain.
- The type of food chains include Grazing food chain, Parasitic food chain, and Detritivorous food chain.
- Food web controls the stability of the ecosystem by maintaining the population level of organisms.
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Sample Questions
Ques 1. Define the concept of trophic level? (1 Mark)
Ans. Trophic level is the position of an organism in a food chain
Ques 2. Why are plants regarded as the primary producers? (1 Mark)
Ans. Plants are efficient for producing food by themselves using the available solar energy.
Ques 3. Define the term apex predator with an example? (1 Mark)
Ans. Apex predators are the topmost predators in the food chain. Lions, Tigers, and Wolfs are included in the list of apex predators.
Ques 4. State the major differences between the food web and the food chain? (2 Marks)
Ans. The Food web is a real concept, whereas, the food chain is hypothetical. Also, the food web is the interlinking of different food chains. The Food Web is not considered straight, whereas, the food chain is straight. The Food web enhances the adaptability and competition among the organisms in the ecosystem.
Ques 5. Why does the energy level decrease along most food chains? (1 Mark)
Ans. A considerable amount of energy is lost in the form of heat moving along the food chain.
Ques 6. How do food webs depict different patterns of energy transfer in terrestrial and aquatic ecosystems? (3 Marks)
Ans. Patterns of energy flow through different ecosystems. The turnover rate of phytoplankton is 10 to 1000 times faster than that of grasslands and forests. Therefore, less carbon is stored in the living autotroph biomass pool, and producer biomass is consumed by aquatic herbivores at 4 times the terrestrial rate. Herbivores in terrestrial ecosystems are less abundant.
Decomposers are much more abundant than in phytoplankton-dominated aquatic ecosystems. In several terrestrial ecosystems with high-standing biomass and relatively low harvest of primary production by herbivores, the detrital food chain is dominant. In deep-water aquatic ecosystems, with rapid turnover of organisms, and a high rate of harvest, the grazing food chain can be considered dominant.
Ques 7. What are decomposers? (2 Marks)
Ans. Decomposers are usually small animals or organisms that eat dead organisms left behind. Examples of decomposers are bacteria, fungi, and mold. They may eat a dead fish that is decomposing and turn what they eat into micronutrients that go into the soil. This process helps in the production of energy that plants use to grow. Without decomposing, there wouldn’t be all the micronutrients that plants use to help them grow.
Ques 8. What are keystone animals in the food web? (2 Marks)
Ans. Keystone animals hold the whole environment together. A salmon is a keystone animal for Idaho. Salmons are important as they travel. Idaho’s salmon go to the Pacific Ocean and there, they eat plankton. They fill up on krill and come back to Idaho, bringing back all the nutrients. Salmons feed so many animals like otters, muskrats, bears, and raccoons. Salmon, for Idaho, is a keystone species because they are a part of so many food chains.
Ques 9. What animal is at the bottom of the food chain? (1 Mark)
Ans. We start with a source of energy, either the sun or the really hot deep-sea vents. This is followed by plants that use that energy. Animals eat those plants which may be eaten along the chain and they die and decompose. The chain is really a web that's all interconnected.
Ques 10. What will happen if the producer in the food chain dies? (2 Marks)
Ans. The removal of the producers would cause the collapse of the entire food web. Primary consumers or herbivores, which feed on producers directly, would die off. Higher level consumers would suffer as organisms from lower trophic levels starts to die off.
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