Graze

All you want to know about Graze

For other uses, see abrasion.

Red Kangaroo (Macropus rufus) grazing.

Grazing generally describes a type of predation in which a 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 (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]. Many small selective herbivores follow larger grazers, who skim off the highest, tough growth of plants exposing tender shoots.

1 Ecological effects
2 Non-mammalian grazing
3 See also
4 References

Ecological effects

A number of ecological effects derive from grazing, and these may be either positive or negative. Negative effects of grazing (or more usually over-grazing) include increased soil erosion, adverse water quality impacts from increased runoff and loss of biodiversity. For example historical grazing, along with other land consversion, in Northern and Central California has reduced native chaparral and forest lands by approximately 70 percent. Ongoing grazing expansion {and land conversion} driven by human population growth in this region threatens the remaining integrity of California montane chaparral habitat in this region.^[2]

In some habitats, appropriate levels of grazing may be effective in restoring or maintaining native grass and herb diversity in rangeland that has been disturbed by overgrazing, lack of grazing (such as by the removal of wild grazing animals), or by other human disturbance. Conservation grazing is the use of domestic livestock to manage such habitats, often to replicate the ecological effects of the wild relatives of livestock, or those of other species now absent or extinct. For example, heathland in Europe requires grazing by cattle, sheep or other grazers to maintain its structure and diversity.

Much grazing land has resulted from a process of clearance or drainage of other habitats such as woodland or wetland^[3]

Non-mammalian grazing

Grazing is typically associated with mammals feeding on grasslands, or more specifically livestock in a pasture. However, ecologists sometimes use the word by extension in a broader sense, to include any organism that feeds on any other species without ending the life of the prey organism.^[4] An example of a grazer that may seem counterintuitive 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 process (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 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 kill the organism by cutting the plant at the base.

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)."
^ C.Michael Hogan (2008) Aesculus californica, Globaltwitcher.com, ed. N. Stromberg
^ (1999) A. Crofts and R.G. Jefferson eds. (1999) Lowland Grassland Management Handbook, chapter 2
^ Begon, M., Townsend, C., Harper, J. (1996) Ecology (Third edition) Blackwell Science, London

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Feeding behaviour of Animals

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