Food Web

Introduction: What is a Food Web?

A food web is made up of all the food chains in a single ecosystem. Each living thing is part of multiple food chains in the given ecosystem. Each food chain is one probable way that energy and nutrients may take as they go through the ecosystem. All of the food chains are interconnected and overlapping in nature. These overlapping food chains in an ecosystem make up a food web.

Each food web consists of three constituents known as trophic levels.

• The first trophic level is producers that produce foods.

• Then second level has consumers and decomposers.

Image 1: Food webs

Producers

Producers create the first trophic level. Producers are also known as autotrophs. They make their own food and need not depend on other organisms for nutrition.

Image 2: Autotrophs and Heterotrophs

Most autotrophs create food via a process called photosynthesis. These organisms usually create a nutrient called glucose from sunlight, carbon dioxide, and water. Plants are the most popular and known type of autotrophs.

However, there are many other kinds of autotrophs available on earth. Algae, and their larger forms known as seaweed, are autotrophic. Phytoplankton, tiny organisms that are found in oceans, are also autotrophs. There are some types of bacteria that are autotrophs. For example, bacteria living in active volcanoes use sulfur, instead of carbon dioxide, to produce their own food in a process that is known as chemosynthesis.

Image 3: Process of Chemosynthesis

Consumers

The next trophic level is made up of animals that consume producers. These organisms are known as consumers.

Consumers are further divided into carnivores (animals that consume other animals) and omnivores (animals that consume both plants and animals). Omnivores, like human beings, consume various types of foods. Human beings eat plants, such as vegetables and fruits. They also consume animals and animal products, including meat, eggs, and milk. Moreover, human beings eat fungi, such as mushrooms. Other organisms that human beings consume include algae, in edible seaweeds like nori that are used to wrap sushi rolls, and sea lettuce which is used in salads. Bears are omnivores and they consume berries and mushrooms, apart from animals such as salmon and deer.

Consumers are mainly divided into three categories: primary, secondary, and tertiary.

• Herbivores are the Primary consumers. Herbivores consume plants, algae, and other producers. They are placed at the second trophic level. Deer, mice, and even elephants are herbivores in a grassland ecosystem. They consume grasses, shrubs, and trees. In a desert ecosystem, a mouse that consumes seeds and fruits is necessarily a primary consumer.

  In an ocean ecosystem, many types of herbivores including fish and turtles are found that eat algae and seagrass. In kelp forests, special types of seaweeds known as giant kelp give shelter and food to an entire ecosystem. Sea urchins are notable and potential primary consumers in kelp forests. These small herbivores consume dozens of kilograms of giant kelp every day.

• Secondary consumers are usually those that eat herbivores. They are placed at the third trophic level. In a desert ecosystem, a snake that eats a mouse is a secondary consumer. In the kelp forest, secondary consumers are sea otters that hunt sea urchins.

• Tertiary consumers consume the secondary consumers. They are placed at the fourth trophic level. For example, in the desert ecosystem, an owl or eagle that preys on a snake are the tertiary consumers.

It is notable that there can be more levels of consumers before a food chain finally reaches the top predator. Top predators are also called apex predators and they eat other consumers. They may be placed at the fourth or fifth trophic level. They usually have no natural enemies except human beings. Lions, for example, are apex predators in the grassland ecosystem. In the ocean ecosystem, fish like the great white shark can be considered apex predators. In the desert ecosystem, mountain lions and bobcats are top predators.

Detritivores and Decomposers

Detritivores and decomposers are organisms that eat nonliving plant and animal remains. For example, scavengers such as vultures consume dead animals. Dung beetles that eat animal feces are decomposers too.

Decomposers, like fungi and bacteria, finish the food chain. Decomposers usually turn organic wastes, such as dead plants, into inorganic materials, including nutrient−rich soil. They complete the life cycle, bringing back the nutrients to the soil or oceans for use by autotrophs. This then begins another completely new series of food chains.

Relation between Food web and Food Chains

Food webs connect many different types of food chains, and therefore many different trophic levels. Food webs can support both long and complicated as well as very short food chains.

For example, grass in a forest produces its own food via photosynthesis. A rabbit in the forest eats the grass. A fox may eat the rabbit. When the fox dies, decomposers like worms and mushrooms break down its dead body, returning the nutrients to the soil for plants like grass.

Algae and plankton are the major producers of marine ecosystems. Tiny shrimp called krill consumes the microscopic plankton. The blue whale preys on thousands of tons of krill every day. Meanwhile, apex predators of the marine ecosystem such as orcas prey on blue whales. When the bodies of large animals such as whales reach the seafloor, decomposers such as worms break down the material. The nutrients removed from the decaying flesh provide nutrients for algae and plankton to start a new series of food chains.

Biomass

Food webs are usually defined by their biomass. Biomass is the energy found in living organisms. Autotrophs, the producers of a food web, change the sun's energy into biomass. Biomass goes on decreasing with each successive trophic level. More biomass is found in lower trophic levels than in higher ones.

Image 4: Pyramid diagram of Biomass

As biomass decreases with each increasing trophic level, we will always find more autotrophs than herbivores in a healthy food web. There must be more herbivores than carnivores. An ecosystem will be balanced only if there is a large number of omnivores and a larger number of herbivores and an even larger number of autotrophs.

A healthy food web should have an abundance of autotrophs, many herbivores, and fewer carnivores and omnivores. This balance maintains the ecosystem and recycles biomass.

It must be noted that every link of the food chain in a food web is connected to at least two others. The biomass of an ecosystem relies on how balanced and connected the food web is. When any one link in the food web is threatened, some or all of the other links are weakened or stressed. The ecosystem's biomass thus declines.

Conclusion

It is important to study and know about the food web for the survival of living beings. As we are part of the food web we must know the limits and ends of our food chains in order to manage our food chains. Without the knowledge of food chains and webs, our survival may face danger. Hence it is very important to study.

Frequently Asked Questions

Qns 1. What are the trophic levels of a food web?

Ans. Each food web consists of three constituents known as trophic levels. The first trophic level is producers that produce foods. Then there are consumers and decomposers.

Qns 2. What do food webs do regarding food chains?

Ans. Food webs connect many different types of food chains, and therefore many different trophic levels. Food webs can support both long and complicated as well as very short food chains.

Qns 3. To how many other food chains does each link of a food web connected?

Ans. Every link of the food chain in a food web is connected to at least two others.