Grazing is a method offeeding in which aherbivore feeds on low-growingplants such asgrasses or other multicellular organisms, such asalgae. Manyspecies of animals can be said to be grazers, from large animals such ashippopotamuses to small aquaticsnails. Grazingbehaviour is a type offeeding strategy within theecology of a species. Specific grazing strategies includegraminivory (eating grasses);coprophagy (producing part-digested pellets which are reingested);pseudoruminant (having a multi-chambered stomach but notchewing the cud); and grazing on plants other than grass, such as onmarine algae.
Grazing's ecological effects can include redistributing nutrients, keeping grasslands open or favouring a particular species over another.
Many small selective herbivores follow larger grazers which skim off the highest, tough growth of grasses, exposing tender shoots. For terrestrial animals, grazing is normally distinguished frombrowsing in that grazing is eating grass orforbs, whereas browsing is eating woody twigs andleaves fromtrees andshrubs.[1] Grazing differs frompredation because the organism being grazed upon may not be killed. It differs fromparasitism because the two organismslive together in a constant state of physical externality (i.e., low intimacy).[2][page needed]Water animals that feed by rasping algae and other micro-organisms from stones are calledgrazers–scrapers.[3]
Graminivory is a form of grazing involving feeding primarily on grass[4] (specifically "true" grasses in thePoaceae).Horses,cattle,capybara,hippopotamuses,grasshoppers,geese, andgiant pandas are graminivores. Giant pandas (Ailuropoda melanoleuca) are obligatebamboo grazers, 99% of their diet consisting of sub-alpine bamboo species.[5]
Forlagomorphs (rabbits,hares,pikas), easily digestible food is processed in the gastrointestinal tract & expelled as regular feces. But to get nutrients out of hard-to-digest fiber, lagomorphs ferment fiber in the cecum (in the GI tract) and then expel the contents ascecotropes, which are reingested (cecotrophy). The cecotropes are then absorbed in the small intestine to utilize the nutrients. This process is different from cows chewing their cud but with similar results.[6]
Capybara (Hydrochoerus hydrochaeris) are herbivores that graze mainly on grasses and aquatic plants,[7][8] as well asfruit and treebark.[9] As with other grazers, they can be very selective,[10] feeding on the leaves of one species and disregarding other species surrounding it. They eat a greater variety of plants during the dry season, as fewer plants are available. While they eat grass during the wet season, they have to switch to more abundantreeds during the dry season.[11] The capybara's jaw hinge is not perpendicular; hence, it chews food by grinding back-and-forth rather than side-to-side.[12]
Like lagomorphs, capybara create, expel & eatcecotropes (cecotrophy) to get more nutrition from their food.They may also regurgitate food to masticate again, similar to cud-chewing by a cow.[13] As with other rodents, the front teeth of capybara grow continually to compensate for the constant wear from eating grasses.[14] Their cheek teeth also grow continuously.[12]
The hippopotamus is a large, semi-aquatic mammal inhabiting rivers, lakes, and mangrove swamps. During the day, they remain cool by staying in the water or mud; reproduction and childbirth occur in water. They emerge at dusk to graze on grasses. While hippopotamuses rest near each other in the water, grazing is solitary. Theirincisors can be as long as 40 cm (16 in) and thecanines (tusks) up to 50 cm (20 in);[15] however, the canines and incisors are used for combat, and play no role in feeding. Hippos rely on their broad, horny lips to grasp and pull grasses which are then ground by themolars.[16] The hippo is considered to be apseudoruminant; it has a complex three- or four-chambered stomach but does not "chew cud".[17]
Although grazing is typically associated withmammals feeding ongrasslands,ecologists sometimes use the word in a broader sense to include any organism that feeds on any other species without ending the life of theprey organism.[18] Use of the term "grazing" varies further; for example, amarine biologist may describe herbivoroussea urchins that feed on kelp asgrazers, even when they kill the organism by cutting the plant at the base.Malacologists sometimes apply the word to aquatic snails that feed by consuming the microscopic film ofalgae,diatoms and detritus—abiofilm—that covers thesubstrate and other surfaces underwater.[citation needed] In marineecosystems, grazing bymesograzers such as somecrustaceans maintains habitat structure by preventing algal overgrowth, especially incoral reefs.[19]
Grazer urine and feces "recycle nitrogen, phosphorus, potassium and other plant nutrients and return them to the soil".[20] Grazing can allow for the accumulation oforganic matter which may help to combatsoil erosion.[21] This acts as nutrition for insects and organisms found within the soil. These organisms "aid incarbon sequestration and water filtration".[20]
When grass is grazed, dead litter grass is reduced which is advantageous for birds such aswaterfowl.[22] Grazing can increasebiodiversity. Without grazing, many of the same grasses grow, for examplebrome andbluegrass, consequently producing amonoculture.
In North Americantallgrass prairies, diversity and productivity are controlled to a large extent by nitrogen availability ... Nitrogen availability in prairies was driven by interactions between frequency of fires and grazing by large herbivores ... Spring fires enhance growth of certain grasses, and herbivores such as bison preferentially graze these grasses, keeping a system of checks and balances working properly, and allowing many plant species to flourish.[23]
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