omnivore

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Ravens are omnivores.

Omnivores (from Latin: omni, meaning "all, everything"; vorare, "to devour") are species that eat both plant and animal material as their primary food sources. They often are opportunistic, general feeders not specifically adapted to eating and digesting either meat or plant material in particular. Many omnivores depend on a suitable mix of animal and plant food for long-term good health and reproduction.

Definition

Omnivore, omnivory and similar derivations are terms of convenience; their significance varies according to context and t both kind and degree. No rigid non-fuzzy definition therefore is either possible or necessary. Traditionally the definition for omnivory is some variation of the form: "including both animal and vegetable tissue in the diet",^[1] which is clear enough for most purposes. However, it is neither absolute nor yet precise, either exclusively or inclusively. It is in fact meaningful only in limited senses, either taxonomically or ecologically, because most herbivores and omnivores eat only a small range of types of plant food; one seldom has reason to refer to an omnivorous pig digging for roots and small animals, as being in the same category as an omnivorous chameleon that eats leaves as well as insects; apart from their taxonomic differences the two have little ecological or dietary overlap.

The term "omnivory" also is not comprehensive because it does not deal with questions of mineral food such as salt licks, or the question of eating life forms that are not included in the kingdoms Animalia and Plantae. As for appeals to etymological points such as that "omnivore" means "eater of everything", no biologist or philologist would take them seriously.

One might be tempted to impose a taxonomic definition, irrespective of actual diet, appealing to the use of Carnivora as a taxon in which, in spite of their being Carnivora, most species in the order eat at least some vegetable matter. However, there are no corresponding taxa called "Omnivora" or "Herbivora", and even if there were, zoologists would not claim either that all Carnivora are carnivores, or that all carnivores are Carnivora. ^[2]

Concerning the phenomena to which terms such as "omnivore" might apply, very few carnivores and herbivores in the normal senses are strictly limited to just one type of tissue in the diet. Even felids and mustelids, animals normally seen as specialist carnivores, often eat a little vegetable matter for various reasons, such as finding it in the guts of prey. Examples of animals that come closest to rigid specialisation in carnivory or herbivory are the likes of parasitoidal insects or insects that are specialist sap-suckers. Naturally biologists take no interest in quibbling about whether, or how strictly, to classify a ruminant as an omnivore on the grounds that a cow might swallow insects on the grass it eats, or even that it may eat old bones as mineral supplements. ^[3] Nor is it rewarding to argue whether to call an animal an omnivore because it eats animal food at one stage of its life, and plant matter at another, even though animals as diverse as some species of waterfowl ^[4] and many beetles in the family Meloidae^[5] begin by eating animal food, and change to plant food as they mature. In some contexts one terminology might validly be most convenient, and in other contexts another.

Consequently "omnivory" is a general term of convenience in many contexts, but intrinsically it is neither specific nor unambiguous; to construct any definitive classification would be pointless. To some extent the same applies to logically related terms for dietary behaviour, such as herbivory and carnivory.

Omnivorous species

Although there are cases of carnivores eating plant matter, as well as examples of herbivores eating meat, the classification "omnivore" refers to the adaptations and main food source of the species in general, so these exceptions do not make either individual animals nor the species as a whole omnivorous. In order for the concept of "omnivore" to be regarded as a scientific classification, some clear set of measurable and relevant criteria would need to be considered to differentiate between an "omnivore" and the other vague but less ambiguous diet categories e.g., faunivore, folivore, scavenger, etc.^[6] Some researchers beleive that ancestors of omnivores primarily ate plants.^[7]

Various mammals are omnivorous by nature, such as pigs^[8], badgers, bears, coatis, hedgehogs, opossums, skunks, sloths, squirrels^[9], raccoons, chipmunks,^[10] mice,^[11] and rats.^[12] Various birds are omnivorous, with diets varying from berries and nectar to insects, worms, fish, and small rodents. Examples include cassowarys, chickens, crows^[13] and related corvids, keas, rallidae, and rheas. In addition, some lizards, turtles, fish, such as piranhas, and invertebrates are also omnivorous.

Most bears are omnivores

Most bear species are considered omnivores, but individual diets can range from almost exclusively herbivorous to almost exclusively carnivorous, depending on what food sources are available locally and seasonally. Polar bears are classified as carnivores, both taxonomically (they are in the order Carnivora), and behaviorally (they subsist on a largely carnivorous diet). Wolf subspecies (including wolves, dogs, dingoes, and coyotes) can live on such vegetable material as grain and fruit products indefinitely but clearly prefer meat. Depending on the species of bear, there is generally a preference for one class of food, as plants and animals are digested differently.

While most mammals may display "omnivorous" behavior patterns depending on conditions of supply, culture, season and so on, they will generally prefer one class of food or another, and when their digestive processes are adapted to a particular class, their long-term preferences will reflect such adaptations. Like most arboreal species, most squirrels are primarily granivores, subsisting on nuts and seeds.^[14] But as with virtually all mammals, squirrels avidly consume some animal food when it becomes available. For example, the American Eastern gray squirrel has been exported to parts of Europe, Britain and South Africa. Where it flourishes, its effect on populations of nesting birds is often serious, largely because of attacks on eggs and nestlings.^[15][16]

Quite commonly, predominantly herbivorous organisms will eagerly eat small quantities of animal food when it happens to become available. Although this is a trivial matter most of the time, omnivorous or herbivorous birds, such as sparrows, often will feed their chicks animal food (largely insects) as far as possible while the need for growth is most urgent.^[17] While scientific classification aims to promote communication and analysis of various differences and similarities between species, the concept of an "omnivore" is broad and could be applied to virtually any mammal if one were to insist on speaking literally.

On close inspection it appears that nectar feeding birds such as sunbirds rely on the ants and other insects that they find in flowers, and monkeys of many species eat maggoty fruit, sometimes in clear preference to sound fruit.^[18] When to refer to such animals as omnivorous or otherwise, is a question of context and emphasis.

See also

• Browsing (herbivory)
• Carnivore
• Consumer-resource systems
• Grazing
• List of feeding behaviours
• List of herbivorous animals
• Omnivore
• Plant-based diet (disambiguation)
• Pollination
• Productivity (ecology)
• Seed dispersal
• Seed predation

References

1. ^ Collocott, T. C. (ed.) (1974). Chambers Dictionary of science and technology. Edinburgh: W. and R. Chambers. ISBN 0-550-13202-3. 
2. ^ Ewer , R. F. (1973). The Carnivores. London: Weidenfeld and Nicolson. ISBN 0-297-99564-2. 
3. ^ Evenari, Michael (ed.) Hot Deserts and Arid Shrublands (Ecosystems of the World Series, Vols 12a and B). Elsevier 1986. ISBN-13: 978-0444422972
4. ^ Maclean, Gordon Lindsay. Roberts' Birds of Southern Africa Publisher: New Holland 1993. ISBN-13: 978-0620175838
5. ^ Skaife, S. H., "African Insect Life", Pub. Longmans, Green & Co., London, 1953.
6. ^ Singer, Michael S.; Bernays, Elizabeth A. (2003). "Understanding Omnivory Needs: A Behavioral Perspective". Ecology 84 (10): 2532–2537. doi:10.1890/02-0397. 
7. ^ "Omnivores’ ancestors primarily ate plants, or animals, but not both". http://www.dnaindia.com/scitech/report_omnivores-ancestors-primarily-ate-plants-or-animals-but-not-both_1677181. Retrieved 17 April 2012. 
8. ^ Brent Huffman. "Family Suidae (Pigs)". UltimateUngulate.com. http://www.ultimateungulate.com/Cetartiodactyla/Suidae.html. Retrieved 2007-12-29. 
9. ^ "Tree Squirrels". The Humane Society of the United States. http://www.hsus.org/wildlife/a_closer_look_at_wildlife/tree_squirrels.html. Retrieved 2009-01-01. 
10. ^ "Eastern Chipmunk". Wonder Club. http://www.wonderclub.com/Wildlife/mammals/easternchipmunk.htm. Retrieved 2009-01-01. 
11. ^ "Florida Mouse". United States Fauna. http://www.unitedstatesfauna.com/floridamouse.php. Retrieved 2009-01-01. 
12. ^ "Brown Rat". Science Daily. http://www.sciencedaily.com/articles/b/brown_rat.htm. Retrieved 2009-01-01. 
13. ^ Seattle Audubon Society. "Family Corvidae (Crows/Ravens)". BirdWeb.org. http://birdweb.org/birdweb/bird_details.aspx?id=318. Retrieved 2011-01-01. 
14. ^ Halle, S. & Stenseth, N. (2000). Activity patterns in small mammals: an ecological approach. Berlin; Heidelberg, Germany; New York: Springer-Verlag.
15. ^ Annex: Towards a Forestry Commission England Grey Squirrel Policy, Forestry Commission, 22 Jan 2006, http://www.forestry.gov.uk/pdf/greysquirrel-annex.pdf/%24FILE/greysquirrel-annex.pdf, retrieved 15 May 2012 
16. ^ Moller, H. 1983. Food and foraging behaviour of red (Scirus vulgaris) and grey (Scirus carolinensis) squirrels. Mammal Review, 13: 81-98
17. ^ Capinera, John. Insects and Wildlife. Publisher: Wiley-Blackwell 2010. ISBN 978-1-4443-3300-8
18. ^ Ewing, Jack. Monkeys Are Made of Chocolate. Publisher: Pixyjack Press 2005. ISBN 978-0-9658098-1-8

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