Grazing generally describes a type of predation in which an herbivore feeds on plants (such as grasses), or more broadly on a multicellular autotrophs (such as kelp). Grazing differs from true predation because the organism being eaten is not killed, and it differs from parasitism as the two organisms do not live together, nor is the grazer necessarily so limited in what it can eat (but see generalist and specialist species). The word "graze" derives from the Old English (OE) grasian, "graze", itself related to OE graes, "grass". For terrestrial animals grazing is normally distinguished from browsing in that grazing is eating grass or other low vegetation, and browsing is eating woody twigs and leaves from trees and shrubs [1]. However, "grazing" is sometimes used to refer to both grazing and browsing. Grazing may be associated with mammals feeding on grasslands, or more specifically livestock on a farm. However, ecologists sometimes use the word in a much broader sense, including any organism that feeds on any other without living in close association with it or ending its life by the act of feeding on it, as described above.[2] An example of a grazer that might seem counterintuitive to the everyday use of the word is a mosquito, which is not a parasite in that it does not form any lasting association with its prey, and is not a true predator in that it does not kill them by this act (although they can act as a vector for fatal diseases such as malaria). In this sense it is the antithesis of parasitoidism, in which an organism (typically the larval stage of a wasp) feeds on another by eating it from within. In that case, the prey is inevitably killed by successful predation, and has an intimate association with its predator, such that its premature death would also see the parasitoid die as well. Use of the term varies however, for example a marine biologist may describe herbivorous sea urchins that feed on kelp as grazers even when they consistently kill the organism by cutting the plant down at the base. Many smaller, selective herbivores follow grazers because they skim off the highest, tough growth of plants exposing tender shoots.
See also
References
- ^ Concise Oxford Dictionary, 1976 (6th ed) ISBN 0-19-861122-6. "Graze, verb: 2. Eat growing grass." "Browse, verb: 1. Feed on, crop, (leaves, twigs, scanty vegetation)."
- ^ Begon, M., Townsend, C., Harper, J. (1996) Ecology (Third edition) Blackwell Science, London
