What are herbivorous animals?

Herbivorous animals are animals that anatomically and physiologically is it so adapted to feed on plant matter, which constitutes the main or exclusive component of their diet. A herbivorous animal can ingest variable amounts of animal foods, for example insects, but these are ingested in a complementary way, or even accidentally.

Humans who feed exclusively on vegetables are not called herbivores, but vegetarians or vegans, terms that refer to habits or customs and not necessarily to physiological or anatomical adaptations of the organism.

Definition and etymology

The word herbivore comes from the Latin grasswhich means plant or grass, and I will eat, which means to eat or devour. One of the earliest written references to the use of this term is found in the book Principles of Geologypublished in 1830 and written by charles lyell.

Although the word herbivore tends to be associated with animals that feed on plants, in a broad definition it would encompass any heterotrophic organism that feeds on autotrophic organisms such as, in addition to plants, algae, fungi and photosynthesizing bacteria, that is, herbivores are those that feed mainly on primary producersand as such they have the ecological role of primary consumers.

However, the term herbivore does not have an exact definition from a biological or ecological point of view, although it is always usually limited to the field of zoology and, therefore, it usually refers to animals and not to other types of organisms. For example, fungi and bacteria that feed on living plants are usually defined as pathogens (causing plant diseases) and those that feed on dead plants are usually classified as detritivores or saprophages.

Role in the food chain

Whether directly or indirectly, virtually all living organisms on planet Earth obtain the energy they need from the Sun. Autotrophic photosynthetic organisms, such as plants, are primary producers and are capable of convert the sun's energy into chemical energy which is stored in various organic molecules, mainly in carbohydrates.

Herbivores are the first animals in the food chain that feed on primary producers, hence they are considered primary consumers. Herbivores are able to take advantage of the energy that the primary producers had obtained from solar radiation and stored in organic molecules.

Carnivores and omnivores, those that occupy the level of secondary consumers, feed on herbivores and obtain energy from them, energy that ultimately also comes from solar radiation.

examples of herbivorous animals

Herbivorous animals are widespread and there is a great variety of different types. Without a doubt, the largest herbivore is the African elephant, which is not only the largest herbivore but also the largest land animal living today; an adult can exceed 5 tons in weight and consume more than 130 kg of vegetables per day, including fruits, roots, grass and leaves.

On the opposite side, it may be that the smallest herbivorous animals are the ptylidsa few tiny beetles with species that do not reach 0.5 mm in length.

By groups, these are some common examples of herbivores:

  • mammals: among the mammals there are large and extensive groups of herbivores, such as cattle (bison, oxen, buffalo, cattle, antelope), camelids (llamas, camels), giraffes, okapi, cervids (deer, elk, roe deer, fallow deer), diprotodonts (kangaroos, koalas), equids (horses, zebras, donkeys), lagomorphs (rabbits, hares, pikas), rodents (squirrels, chinchillas, capybaras, beavers, mice, octodontids), elephants, hippopotamuses, rhinos, tapirs, and a long and so on. There are even herbivorous aquatic mammals, the sirenians (manatees, dugongs).
  • reptiles: examples of herbivorous reptiles are the testudinids (a family of herbivorous land turtles), iguanas, the skinks of the Solomon Islands or many species of the extinct dinosaurs.
  • birds: there are many species of herbivorous birds, for example parrots, parakeets, sandgrouse, hoatzin, or species of ducks, geese and gander that feed mainly on algae and aquatic plants.
  • amphibians: the tadpoles of many species of frogs have a basically herbivorous diet. Some sirenids (close to salamanders) have semi-herbivorous habits.
  • Fishes: there are not many herbivorous fish but they usually have a very important ecological role. For example, unicorn fish, surgeon fish, cajetas or escaros. Other aquatic animals, such as sea snails, shrimps, crabs and other crustaceans, could also be considered herbivores.
  • Insects and other invertebrates: Many insects are completely herbivorous, for example bees, butterflies, grasshoppers, leafhoppers, leafhoppers (leafhoppers), moths, and many species of ants. They are also herbivorous larval stages of many insects, snails and slugs; earthworms are detritivores that feed largely on dead plant matter.

Featured Adaptations

The digestive system of carnivorous and herbivorous animals usually have very important differences. An outstanding example is found in the ruminant mammals that they have multiple stomach chambers and long digestive tracts. They also have flat teeth that help grind up plant matter, while carnivores typically have a single stomach and sharp teeth.

Ruminants are also characterized by regurgitate the food back to the mouth from its first stomach for a second chew before moving on to the second stomach. This process is repeated until the food passes through all the stomach chambers, in most ruminants 4.

Digestive system and stomachs of a cow
Diagram of the digestive system of a cow

The adaptations of ruminants and other herbivorous animals most often include symbiotic relationships with bacteria that live in the digestive tract and that produce enzymes capable of digesting cellulose (cellulase), lignin and other plant substances that animals alone cannot digest.

These symbiotic bacteria are also the source of vitamin B12 for ruminants, an essential vitamin for all mammals, including humans, but that only bacteria can synthesize.

In addition to ruminants, many other animals have specific adaptations for herbivorous feeding. For example, earthworms produce substances called drilodefensins that have surfactant action and help digest plant material.

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