Trophic Levels in a Food Chain: Definition & Explanation

Instructor: Margaret Cunningham
This lesson will explore the feeding relationships of organisms in an ecosystem, including food chains and food webs. The lesson will also investigate the different trophic levels of a food chain and give examples of species found at each level.

Introduction

Think about the food you ate today. Did you eat any plant materials? Did you eat anything that when it was alive might have eaten another organism? Organisms, including humans, are often classified by their feeding relationships. In other words they are organized by who eats whom and this classification system is called a food chain. A food chain is a sequence of organisms that feed on each other. Although the design of a food chain can vary by ecosystem, all food chains are made up of the same basic trophic levels. Trophic levels are the levels within the food chain where an organism obtains its energy.

In most food chains there are five main trophic levels, but the number can vary depending on the composition of the ecosystem. Ecosystems with fewer species may have a food chain with three trophic levels, while an ecosystem with a large number of species is more likely to have a food chain with more than five trophic levels.

Simple Food Chain
food chain

Trophic Levels

The first trophic level contains the greatest number of organisms and is comprised mainly of plants. The organisms in this layer are called primary producers because they get their energy from an abiotic source. Most primary producers get their energy directly from the sun. Primary producers are important to the whole food chain because they are the original source of energy that is then passed between other organisms.

The next three trophic levels contain organisms known as consumers. Consumers are organisms that get their energy from eating other organisms. The second level contains organisms that gain their energy by eating primary producers and they are called primary consumers. Primary consumers are also called herbivores, which are organisms that have a diet comprised entirely of vegetation and include such organisms as deer, rabbits, and sheep.

The third trophic level contains organisms called secondary consumers. Instead of eating plants like primary consumers, the secondary consumers are often referred to as carnivores because they eat meat, and in this case they eat the meat of the primary consumers in the level below them. Secondary consumers include such organisms as snakes, insect-eating birds, and frogs.

The fourth level contains organisms called tertiary consumers. Species that are tertiary consumers are often referred to as top predators because they consume organisms in both of the consumer levels below them and because they often do not have any natural predators that eat them. Tertiary consumers include species such as wolves, coyotes, mountain lions, and orcas.

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