34.2: Digestive Systems - Herbivores, Omnivores, and Carnivores
- Differentiate among herbivores, omnivores, and carnivores
Herbivores, Omnivores, and Carnivores
Herbivores are animals whose primary food source is plant-based. Examples of herbivores include vertebrates like deer, koalas, and some bird species, as well as invertebrates such as crickets and caterpillars. These animals have evolved digestive systems capable of digesting large amounts of plant material. The plants are high in fiber and starch, which provide the main energy source in their diet. Since some parts of plant materials, such as cellulose, are hard to digest, the digestive tract of herbivores is adapted so that food may be digested properly. Many large herbivores have symbiotic bacteria within their guts to assist with the breakdown of cellulose. They have long and complex digestive tracts to allow enough space and time for microbial fermentation to occur. Herbivores can be further classified into frugivores (fruit-eaters), granivores (seed eaters), nectivores (nectar feeders), and folivores (leaf eaters).
Omnivores are animals that eat both plant- and animal- derived food. Although the Latin term omnivore literally means “eater of everything”, omnivores cannot really eat everything that other animals eat. They can only eat things that are moderately easy to acquire while being moderately nutritious. For example, most omnivores cannot live by grazing, nor are they able to eat some hard-shelled animals or successfully hunt large or fast prey. Humans, bears, and chickens are examples of vertebrate omnivores; invertebrate omnivores include cockroaches and crayfish.
Carnivores are animals that eat other animals. The word carnivore is derived from Latin and means “meat eater.” Wild cats, such as lions and tigers, are examples of vertebrate carnivores, as are snakes and sharks, while invertebrate carnivores include sea stars, spiders, and ladybugs. Obligate carnivores are those that rely entirely on animal flesh to obtain their nutrients; examples of obligate carnivores are members of the cat family. Facultative carnivores are those that also eat non-animal food in addition to animal food. Note that there is no clear line that differentiates facultative carnivores from omnivores; dogs would be considered facultative carnivores.
Key Points
- Herbivores are those animals, such as deer and koalas, that only eat plant material.
- Omnivores are those animals, such as bears and humans, that can eat a variety of food sources, but tend to prefer one type to another.
- While most carnivores, such as cats, eat only meat, facultative carnivores, such as dogs, behave more like omnivores as they can eat plant matter along with meat.
- Facultative carnivores can eat meat as well as plant material while obligate carnivores eat meat all the time.
Key Terms
- omnivore : an animal which is able to consume both plants (like a herbivore) and meat (like a carnivore)
- obligate carnivore : an animal that necessarily subsists on a diet consisting mainly of meat because it does not possess the physiology to digest vegetable matter
- herbivore : any animal that eats only vegetation (i.e. that eats no meat)
- carnivore : any animal that eats meat as the main part of its diet