Herbivores are animals that only eat plants. They are herbivorous animals including humans.
Humans are believed to be omnivores, because they eat meat as well as vegetable matter. However, research has shown that humans are more suited to a carnivore diet because of the shape and make up of our hands and feet. People who eat mostly plants are usually called vegetarian.
Herbivores (such as deer, elephants, horses) have teeth that are adapted to grind vegetable tissue. Many animals that eat fruit and leaves sometimes eat other parts of plants, for example roots and seeds. Usually, such animals cannot digest meat. But some herbivorous animals will eat eggs and occasionally other animal protein.
The diets of some herbivorous animals change with the seasons. In the temperate zones of the Earth, some seasons are hot and some are cold, so different plants are available at different times of the year.
Plant cell walls are mostly made up of cellulose. No herbivore can digest cellulose by itself. They all make use of gut flora, some of which produce an enzyme called cellulase. This is an example of symbiosis.
According to the theory of predator-prey interactions, the relationship between herbivores and plants is cyclic. When prey (plants) are numerous their predators (herbivores) increase in numbers, reducing the plant population, which in turn causes herbivore number to decline. The prey population eventually recovers, starting a new cycle. This suggests that the population of the herbivore fluctuates around the carrying capacity of the food source, in this case the plant.
There will always be pockets of plants not found by herbivores. This is important for specialist herbivores which feed on only one species of plant: it prevents these specialists from wiping out their food source. Eating a second plant type helps herbivores’ populations stabilize. Alternating between two or more plant types provides population stability for the herbivore, while the populations of the plants oscillate. When an invasive herbivore or plant enters the system, the balance is thrown off and the diversity can change or even collapse.
In some ways it is easier to be an herbivorous animal than a carnivorous (meat-eating) animal. Carnivorous animals have to find and catch the animals that they eat, and sometimes the animals that they want to eat fight them. Herbivorous animals have to find the plants that they want to eat, but they do not have to catch them. Many plants have some defence against herbivores, such as spines, toxins (poisons), or a bad taste. There are many more herbivorous animals living in the world than carnivorous animals.
Some examples of herbivores
- Gotelli N.J. 1995. A primer of ecology. Sinauer.
- Smith R.L. & T.M. 2001. Ecology and field biology. 6th ed, Cummings, New York.