What is A Food Chain?

A food chain is the group of organisms linked in order of the food they eat, from producers to consumers, and from prey, predators, scavengers, and decomposers.

But of course one organism can eat more than one other organism, right?  Thus, we have food webs.

A food web is all related food chains in an ecosystem.

A food chain is broken down into three trophic levels.  A trophic level is one of three positions on the food chain: autotrophs (first), herbivores (second), and carnivores and omnivores (third).

Living things need energy to grow, breathe, reproduce, and move. Energy cannot be created from nothing, so it must be transferred through the ecosystem.

The primary source of energy for nearly every ecosystem on earth is the Sun.

The first in the trophic levels is producers.  Producers, also known as autotrophs, make their own food. They make up the first level of every food chain. Autotrophs are usually plants or one-celled organisms. Nearly all autotrophs use a process called photosynthesis to create “food” (a nutrient called glucose) from sunlight, carbon dioxide, and water.  Plants use energy from the Sun to create their own food in photosynthesis.
Plants are the most familiar type of autotroph, but there are many other kinds. Algae, whose larger forms are known as seaweed, are autotrophic. Phytoplankton, tiny organisms that live in the ocean, are also autotrophs.

The second trophic level consists of organisms that eat the producers. These are called primary consumers, or herbivores.  Secondary consumers are carnivores (animals that gain their energy by eating other animals) eat the herbivores.

Tertiary consumers eat the secondary consumers. Tertiary predators are carnivores that eat other carnivores.  In the example below, the herbivore, or the primary consumer, is the grasshopper.   The mouse is the secondary consumer, and the snake is the tertiary consumer.

There may be more levels of consumers before a chain finally reaches its top predator. Top predators, also called apex predators, eat other consumers.  Apex predators, or top predators, have no known predators of their own.  The owl is the apex predator in the example shown below.

Detritivores and decomposers are the final part of food chains. Detritivores (or scavengers) are organisms that eat nonliving plant and animal remains. For example, scavengers such as vultures eat dead animals.

Decomposers like fungi and bacteria complete the food chain. They turn organic wastes, such as decaying plants, into inorganic materials, such as nutrient-rich soil. Decomposers complete the cycle of life, returning nutrients to the soil or oceans for use by autotrophs. This starts a whole new food chain. 

Since a food web is representative of an entire community, it will consist of multiple food chains that are intertwined. There are usually multiple predator species that feed on a particular prey species, and one predator species usually feeds on multiple prey species. The same goes for the relationship between plants and herbivores.

A food web describes the many species and interactions within an ecosystem. Mapping these interactions can show us how an entire ecosystem could fall apart if it loses even one species.