Omnivores
Omnivores are animals that have the ability to consume both plant and animal foods. This dietary flexibility allows them to adapt to varying food availability, which can be particularly advantageous in changing environments. Unlike herbivores, who primarily eat plants and require complex digestive systems to break down tough plant materials, and carnivores, who rely on hunting other animals, omnivores have digestive tracts that accommodate a wider range of food sources. While they can eat various items, they generally do not digest tough plant matter as efficiently as larger herbivores.
Omnivores include a diverse array of species, such as raccoons, bears, certain birds like robins and ostriches, and various fish and mollusks. For example, raccoons consume insects, fruits, and even carrion, showcasing their adaptability. Additionally, studies have highlighted the evolutionary advantages of omnivorous diets, linking them to enhanced survival during periods of environmental change and food scarcity. The role of omnivores in ecosystems is also a subject of ongoing research, as they contribute to various ecological dynamics. Understanding omnivores provides insight into dietary behaviors and the resilience of species in the face of global climate challenges.
On this Page
Subject Terms
Omnivores
Many animals are either herbivores, who eat only plant food, or carnivores, who eat only the flesh of other animals. The preference for one type of food or the other depends largely on the type of digestive system that the animal has and the resources it can put into its “energy budget.” Meat is generally easier to digest and requires a less complex digestive system and a relatively short intestinal tract. However, to get meat, carnivores must invest a lot of time hunting their prey, and the outcome of a hunt is always uncertain. The food of herbivores is much easier to obtain since plants do not move, and all the herbivore has to do is graze on the grasses, leaves, or algae readily available around it. However, the cellulose that plants are made of is very tough to digest, and thus, herbivores must have a much more complex and lengthier digestive tract than carnivores. Many herbivores are ruminants with multipart stomachs who have to chew and digest their food more than once to get adequate nutrition.
Carnivores and herbivores are also vulnerable to a loss of their food source. Herbivores whose digestive systems are specialized to process only one type of food will starve if that food becomes scarce due to drought or other climatic changes. Carnivores often have specialized hunting patterns that cannot be changed if the prey (usually herbivores) becomes scarce due to the loss of their food source.
Omnivores maximize their ability to obtain food by having digestive tracts capable of processing both plant and animal food. However, they are usually incapable of digesting the very tough plant material, such as grasses and leaves, that many large herbivores eat. Omnivores may also be scavengers, eating whatever carrion they may come across. Omnivores often lack the specialized food-gathering ability characteristic of pure carnivores and herbivores. Many animals, often called carnivores, are actually omnivores, eating plants and animals. Some species of foxes are known for hunting small mammals, such as rabbits, but they also eat fruit. Squirrels mainly subsist on fruit, nuts, and seeds but also eat small birds and insects.
Types of Omnivores
Omnivores include all types of animals living on land and in water, including fish, mollusks, arthropods, birds, and mammals.
Most insects are either herbivores, such as grasshoppers, or carnivores, such as mantises. However, some, like yellow jacket wasps, are omnivores, eating other insects, fruit, and nectar. Omnivorous snails and slugs eat algae, leaves, lichens, insects, and decaying plant and animal matter. Their main organ for eating is called a radula, a tonguelike, toothed organ drawn along rocks, leaves, or plants to scrape off food; it is also used to bore holes through the shells of other mollusks, to get to their flesh.
Omnivorous fish include the common carp, goldfish, catfish, eels, and minnows. Since a fish’s food is often suspended in the medium through which the fish swims—water—being able to gulp up whatever comes into its mouth is an efficient way for a fish to eat. Similarly, bottom-feeders (fish that suck up material from the floor of whatever body of water they inhabit) also benefit from not needing to sort through the material before they ingest it.
Many birds are omnivores, such as robins, ostriches, and flamingos. Flamingos are pink or red because they eat blue-green algae and higher plants, which contain the same substances that make tomatoes red. They also eat shrimp and small mollusks.
Mammal omnivores include bears, members of the weasel family, such as skunks, the raccoon family (raccoons and coatimundis), monkeys, apes, and humans. Raccoons and coatis, found only in the Americas, eat insects, crayfish, crabs, fishes, amphibians, birds, small mammals, nuts, fruits, roots, and plants. Like other omnivores, they also eat carrion. Bears eat grass, roots, fruits, insects, fishes, small or large mammals, and carrion. Squirrels, usually considered herbivores because of their association with gathering nuts and seeds, are also omnivores who will eat insects, bird eggs, baby birds, small rodents, and carrion.
The study and understanding of omnivores, their diet, and their behaviors have attracted increased attention in the twenty-first century, especially in the wake of global climate change. Recent studies suggest that animals that were omnivores, including humans, had a distinct evolutionary advantage. They were able to survive in times of environmental change and food scarcity. Scientists are also investigating the link between omnivore animals and increased cognitive function. They also continued to study omnivore’s unique role in the ecosystem.
Principal Terms
Carnivore: a flesh-eating animal
Carrion: dead animals
Diurnal: active during the day
Herbivore: an animal that eats only plants
Radula: a tonguelike, toothed organ for grinding food
Bibliography
Kay, Ian. Introduction to Animal Physiology. New York: Springer-Verlag, 1999.
Lauber, Patricia. Who Eats What? New York: HarperTrophy, 1995.
Llamas, Andreu. Crustaceans: Armored Omnivores. Milwaukee: Gareth Stevens, 1996.
McGinty, Alice B. Omnivores in the Food Chain. Logan, Iowa: Powerkids Press, 2002.
"Omnivores." National Geographic Society, 19 Oct. 2023, education.nationalgeographic.org/resource/omnivores. Accessed 24 Sept. 2024.
"Omnivore Animals." Animalia Bio, animalia.bio/omnivore?page=8. Accessed 24 Sept. 2024.