A food web is all of the interactions between the species within a community that involve the transfer of energy through consumption. A food web incorporates different food chains within an environment. These types of interactions occur between producer and consumer, and between predator and prey.

The transfer of energy starts with plants. Plants are able to convert sunlight into a chemical form of energy through the process of photosynthesis. One of the end products of photosynthesis is glucose, a sugar in which energy is stored. Plants are called producers because they produce their own energy without consuming another organism.

Animals are called consumers; they must consume plants and other animals to obtain energy. Animals that feed only on plants are called herbivores, or primary consumers since they eat producers. Animals that feed on other animals are called carnivores. They are called secondary consumers if they eat primary consumers. Another kind of secondary consumer is an omnivore, which is an animal that feeds on both plants and other animals. Any animal that hunts and feeds on other animals is called a predator, and the animals that predators feed on are called prey. All carnivores are predators, and herbivores—and sometimes omnivores or other carnivores—are their prey. 

Energy moves up a food chain, starting with plants, then moving up through herbivores, and then carnivores. A fourth group of organisms called decomposers breaks down the organic matter left behind by these other organisms, like dead animals or plants. Organisms within each group gain energy by feeding on the organisms in the group below them on the food chain. The top predator of a food chain is the carnivore within the community that does not have any predators of its own. When the top predator dies, their remains are broken down by decomposers—bacteria and fungi. Decomposers return nutrients back to soil to help restart the food chain.

An example of a marine food chain starts with seaweed as the producer, which is then fed on by zooplankton. From there, crustaceans will consume the zooplankton, and larger fish will consume the crustaceans. At this point, the fish will be eaten by squids, and finally, the squids will be devoured by sharks. Sharks are a top predator with no predators of their own, so they are at the top of the food chain.

The amount of available energy decreases as it moves up the food chain. This is because only plants are able to produce energy in the first place, and at each step of the food chain energy is lost in the form of heat as the organism maintains their body and performs daily functions.  

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.

 

Food Webs

A white tailed deer (Odocoileus virginianus) eating leaves from a bush in Ottawa, Canada. Deer are key members of the food web. 

Noun

organism that eats meat.

community
Noun

group of organisms or a social group interacting in a specific region under similar environmental conditions.

consumer
Noun

organism on the food chain that depends on autotrophs (producers) or other consumers for food, nutrition, and energy.

crustacean
Noun

type of animal (an arthropod) with a hard shell and segmented body that usually lives in the water.

decomposer
Noun

organism that breaks down dead organic material.

glucose
Noun

"simple sugar" chemical produced by many plants during photosynthesis.

Noun

organism that eats mainly plants and other producers.

Noun

organism that eats a variety of organisms, including plants, animals, and fungi.

organism
Noun

living or once-living thing.

Noun

process by which plants turn water, sunlight, and carbon dioxide into water, oxygen, and simple sugars.

predator
Noun

animal that hunts other animals for food.

prey
Noun

animal that is hunted and eaten by other animals.

producer
Noun

organism on the food chain that can produce its own energy and nutrients. Also called an autotroph.

zooplankton
Plural Noun

microscopic, heterotrophic organism that lives in the ocean.