Secondary Consumer

Secondary Consumer Definition

Secondary consumers are organisms that eat primary consumers for energy. Primary consumers are always herbivores, or organisms that only eat autotrophic plants. However, secondary consumers can either be carnivores or omnivores. Carnivores only eat other animals, and omnivores eat both plant and animal matter. Regardless of what a secondary consumer is, it still must have primary consumers in its diet to survive.

Examples of Secondary Consumers

Secondary consumers come in all shapes, sizes, and exist in practically every habitat on earth. Icy tundras, arid savannahs, and artic waters are just some of the extreme environments secondary consumers live in. Whether on land or in water, the one thing they have in common is the type of food they eat—primary consumers.

Aquatic environments are capable of supporting several types of secondary consumers because of the vast amount of food sources available. Piranhas are an example of aquatic omnivores that eat fish, snails, aquatic plants, and even birds. Smaller, less predatory sharks can also be considered secondary consumers because larger sharks, whales, or fish often hunt them. If there were no aquatic secondary consumers, then primary consumers would have no population regulation. This would lead to the over-consumption of primary producers, like phytoplankton, which make up the first trophic level. Phytoplankton produce over 70% of earth’s oxygen; without them (and other autotrophs like them) life could not exist.

Terrestrial habitats can vary greatly, from freezing habitats with below zero temperatures to nearly waterless desserts along the equator. Luckily, secondary consumers have adapted to exist in every type of ecosystem. Temperate regions are home to moles, birds, and other secondary consumers such as dogs and cats. Long ago, even humans were considered secondary consumers because other mammals could easily hunt them. However, with the help of evolution and new technology, humans are now considered the ultimate tertiary consumer.

What is unique about secondary consumers is that they can sometimes also be considered primary or tertiary consumers depending on the environment. For example, when squirrels eat nuts and fruits, it is a primary consumer. If a squirrel switches to eating insects or baby birds, then it is considered a secondary consumer. This type of switching can occur at any time, in any environment, depending on food and predators in the area, as shown below.

Food web diagram

Functions of Secondary Consumers

Secondary consumers are an important part of the food chain. They control the population of primary consumers by eating them for energy. Secondary consumers also provide energy to the tertiary consumers that hunt them. Scientists keep track of the energy movement through consumers by grouping them into tropic levels.
The most self-sufficient organisms, like plants and other autotrophs, are on the bottom of the pyramid because they can make their own energy. This is the first trophic level. Primary consumers (herbivores) make up the second tropic level; secondary consumers make up the third tropic level, and so forth as show below:

Trophic levels

As the pyramid shows, energy is lost as it moves up trophic levels because metabolic heat is released when an organism eats another organism. The bottom of the pyramid makes 100% of its own energy. By the time a secondary organism eats, they only receive 1% of the original energy available.

In order to provide enough energy to the top tiers of the pyramid, there must be many more producers and plant-eaters than anything else. However, needing fewer secondary consumers does not make them less important. There is a delicate balance within the food chain. If there are not enough secondary consumers, then tertiary consumers face starvation (or worse—extinction) because they would no longer have a food supply. If there are too many secondary consumers, then they will eat more and more primary consumers until they are on the brink of extinction. Both of these extremes would disrupt the natural order of life on Earth.

Ecological Pyramid

Types of Secondary Consumers

Secondary consumers can be sorted into two groups: carnivores and omnivores.

Carnivores only eat meat, or other animals. Some secondary consumers are large predators, but even the smaller ones often eat herbivores bigger than they are in order to get enough energy. Spiders, snakes, and seals are all examples of carnivorous secondary consumers.

Omnivores are the other type of secondary consumer. They eat both plant and animal materials for energy. Bears and skunks are examples of omnivorous secondary consumers that both hunt prey and eat plants. However, some omnivores are simply scavengers. Instead of hunting, they eat the excess animal remains that other predators leave behind. Opossums, vultures, and hyenas are some animals that gain energy through scavenging.

Related Biology Terms

  • Trophic levels – The hierarchical level an organism fits into based on its position in the food chain.
  • Primary producers – Organisms that can produce their own food and energy. Also known as autotrophs.

Quiz

1. Secondary consumers often:
A. Produce their own energy
B. Are strictly herbivores
C. Hunt tertiary consumers
D. Feed on primary consumers

Answer to Question #1

2. Energy is:
A. Gained as trophic levels increase
B. Acquired when secondary consumers eat producers
C. Lost as trophic levels increase
D. Only gained through hunting prey

Answer to Question #2

3. Which of the following is in the correct order based on trophic levels (lowest to highest):
A. Plant, Lion, Squirrel
B. Squirrel, Plants, Eagle
C. Eagle, Squirrel, Plant
D. Plant, Rabbit, Dog

Answer to Question #3
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