An omnivore is an organism that can feed on both plant and animal sources. Carnivores are animals that feed only on other animals. Herbivores feed exclusively on plant material. An omnivore can feed on both sources. Oftentimes, mostly herbivorous animals supplement their diets with small amounts of insects or other animals. In other species, an almost equal amount of meat and plant materials are eaten. In other species, plants are used to supplement the diet when meat supplies are low. Many animals have evolved to eat whatever is available, be it plant or animal.
Although a species as a whole may be omnivores, not all members of the species must be omnivores. Across the human species, while many are omnivorous just as many are vegan and partake in no animal products. In this case, humans are physiologically omnivorous, in that it is possible for them to obtain nutrients from both sources. However, many people are behaviorally herbivorous, and choose not to eat animal products because they can derive all the nutrients they need without animal products. One theory of human evolution suggests that our ancestors were mainly herbivorous, switching to become omnivores when tools and fire aided in the capture and edibility of animals. Below are some more examples of omnivore animals.
Examples of Omnivore
Example #1: Dogs
Geneticists have known for many years that dogs and wolves are closely related. Many theories have existed as to how dogs evolved from their wild counterparts. An early theory suggested that early people kidnapped wolf pups and raised them to be tame. However, this theory did not account for the fact that wolves are obligate carnivores, meaning they feed on only meat, while dogs are omnivores. Researchers studying feral dog behavior around large cities began to notice a pattern of friendlier dogs getting more access to choice scraps of food.
A newer theory on dog evolution extrapolates this fact to dog’s early ancestors. Scientist theorize that these early ancestors were wild wolves exploiting the benefits of early human societies. All societies generate a large amount of waste, and throughout human history, we have piled it just outside civilization. This set-up rewards wolves that venture closer to humans with nutritious scraps. These scraps are not always meat. Evolution then rewards the wolves who are able to process all the scraps, even the plant material. The extra nutrition allows these wolves to reproduce more. Eventually, the group of wolves that exists around humans become much friendlier, in response to human feeding, and humans are able to domesticate them. The artificial breeding of the tame wolves throughout many centuries of domestication is why the dog looks so much different from the wolf.
In fact, the species that contains dogs Canis lupus has over 30 subspecies, which have a variety of diets. These species include the dingo, the domestic dog, and many distinct species of wolf. Wolf species that rely on large mammals as a sole source of food are seeing large declines in their populations. Other wolves, dingoes, and especially dogs, have wildly diversified their diet to coincide with the left-overs of human civilization. These populations are not in decline. Many have become nuisance animals, as they make their way into human developments in search of food. A close cousin of the wolf and dog, the coyote has invaded many subdivisions, and increased human-wildlife conflicts are the result.
Example #2: Bears
Bears are a classic omnivore. Being mostly a scavenger, bears spend their days wandering the woods, mountains, and sometimes even suburbia looking for leftovers. Most mountain communities must protect their trash from these large and powerful omnivores. Bears need an enormous amount of energy during the summer months, to fatten up for their winter hibernation. Some bears hibernate for up to 7 months of the years. This means that during the other 5 months of the year, enough energy must be gathered to allow the bear to stay warm in the den all winter.
To do this, bears are omnivores, and will eat almost any source of nutrition they can find. For plants, bears eat many wild plants including berries, roots, and all kinds of nuts. Although bears don’t typically eat individual flowers, they love to eat honey, and will often fight through the swarm of bees to get to it. As for meat, bears are typically scavengers, and will eat any carcass they come upon. Sometimes, a bear will chase another predator away to claim a kill. Many brown and grizzly bears are also known to eat fish, and have learned to grab the fish from rivers. This large variety in the diet allows bears to obtain enough energy for winter months.
- Humans: Humans have a wide range of diets, from completely herbivorous to almost entirely carnivorous, but most humans eat some amount of both meat and plants.
- Pigs Pigs are often used to study human digestion because of how similar their gut is to ours. Pigs can eat a wide variety of plant an animal materials. Pigs have been known to eat carcasses as scavengers, but are rarely predators, unless they are digging up small insects.
- Crows: Many large birds are scavengers, and will eat whatever they can find. Crows can subsist on stores of grain, small insects, and carrion.
- Ants: Ants are some of the smallest omnivores. Ants typically harvest plant material as food, but will easily convert an intruder to the colony into dinner as well.
- Badgers: Much like bears, badgers also hibernate, and eat a variety of plants, insects, and small animals to gain weight.
- Chipmunks: Though consisting of a diet mostly of nuts, chipmunks will often eat a variety of animals, including insects, crabs, frogs, worms and bird eggs.
- Mice: Mice are often opportunistic feeders, eating anything they can find.
- Opossums: The only North American marsupial mammal, being an omnivore has allowed the opossum to spread from South America. The opossum occupies a similar niche to raccoons, subsisting on carrion and the left-overs from human civilization.
- Chimpanzees: Chimpanzees have been found to hunt and eat small animals, in addition to their mainly plant-based diet.
- Chickens: Chickens eat a variety of insects, but will also eat small rodents, other birds, and eggs. However, a chicken can also subsist only on grains and plant material.
- Turtles: Many turtles, both aquatic and terrestrial will eat plants, fish, and insects, according to what they can catch.
- Lizards: Although many lizards feed only on insects, many feed only on plants, and there are some that feed on both.
Related Biology Terms
- Carnivore – An animal that consumes other animals solely as a source of food.
- Herbivore – An animal that consumes only plants as a source of nutrition.
- Detritivore – Organisms that feed off of dead and decaying plant and animal matter, such as many fungi.
- Autotroph – Unlike the previous three heterotrophs, which must obtain glucose from an outside source, autotrophs produce their own glucose through an environmental energy source.
1. An animal consumes mostly leaves as a source of nutrition. The animal sometimes eats leaves with bugs on them, and the bugs can be digested and converted to energy. However, the animal avoids leaves with bugs. What is the animal?
A. Physiological Omnivore
B. Behavioral Herbivore
2. A predatory fish eats a smaller fish. The smaller fish had eaten a large amount of plant material. The predatory fish can digest the entire smaller fish, but cannot digest the plant material. The plant material passes through the predator, and is excreted. What is the predator?
3. A fungus exists that survives on the forest floor. When plants or animals die, the fungus can use the nutrients of the corpse to survive. The fungus does not discriminate between plant and animal tissue. What is the fungus?