Omnivores (from Latin: omni, meaning "all, everything"; vorare, "to devour") are species that eat both plants and animal material as their primary food source. They often are opportunistic, general feeders not specifically adapted to eating and digesting either meat or plant material primarily. Many 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 the requirements of communication in a range of fields in which such attributes are matters of 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 barely meaningful, because most herbivores and omnivores eat only a small range of types of plant food; there is little value to classifying an omnivorous pig digging for roots and small animals, with an omnivorous chameleon that eats leaves as well as insects; 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, we find that 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, that normally are seen as specialist carnivores, often eat a little vegetable matter for various reasons, such as finding it in the guts of prey. The closest we find to rigid specialisation is in the diet 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 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 might validly find it convenient to use one terminology, and in others another.
In summary "omnivore" 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.
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.
Pigs are a well-known example of omnivores.[6] The crow is another example of an omnivore.[7]
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. Wolf subspecies (including wolves, dogs, dingoes, and coyotes) can live on such vegetable material as grain and fruit products indefinitely but clearly prefer meat; given a choice, dogs are much more carnivorous than humans.
Various mammals are omnivorous by nature, such as pigs, badgers, bears, coatis, hedgehogs, opossums, skunks, sloths, squirrels,[8] raccoons, chipmunks,[9] mice,[10] and rats.[11] Also, some primates are omnivorous, including chimpanzees and baboons.[12][13] Various birds are omnivorous, whose diet varies from berries and nectar to insects, worms, fish, and small rodents; examples include cassowarys, chickens, crows and related corvids, keas, rallidae, and rheas. In addition, some lizards, turtles, fish, such as piranhas, and invertebrates are also omnivorous.
While virtually all mammals may display "omnivorous" behavior patterns depending on conditions of supply, culture, etc., mammals will generally prefer one class of food or another, with optimized digestive processes. Like most arboreal species, most squirrels are primarily granivores, preferring nuts and seeds.[14] But as with virtually all mammals, squirrels can resort to consuming some meat as fallback food if starving or facultatively, e.g., when nests are in danger of being raided by predators, etc.
Depending on the species of bear, there is generally a preference for one class of food, as plants and animals are digested differently.
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 since disease risks and the quality of digestion are often not considered. There are social, psychological and non-nutritive factors that influence diet behavior.
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.[15]
References
- ^ Collocott, T. C. (ed.) (1974). Chambers Dictionary of science and technology. Edinburgh: W. and R. Chambers. ISBN 0550132023.
- ^ Ewer , R. F. (1973). The Carnivores. London: Weidenfeld and Nicolson. ISBN 0297995642.
- ^ Evenari, Michael (ed.) Hot Deserts and Arid Shrublands (Ecosystems of the World Series, Vols 12a and B). Elsevier 1986. ISBN-13: 978-0444422972
- ^ Maclean, Gordon Lindsay. Roberts' Birds of Southern Africa Publisher: New Holland 1993. ISBN-13: 978-0620175838
- ^ Skaife, S. H., "African Insect Life", Pub. Longmans, Green & Co., London, 1953.
- ^ Brent Huffman. "Family Suidae (Pigs)". UltimateUngulate.com. http://www.ultimateungulate.com/Cetartiodactyla/Suidae.html. Retrieved 2007-12-29.
- ^ Seattle Audubon Society. "Family Corvidae (Crows/Ravens)". BirdWeb.org. http://birdweb.org/birdweb/bird_details.aspx?id=318. Retrieved 2011-01-01.
- ^ "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.
- ^ "Eastern Chipmunk". Wonder Club. http://www.wonderclub.com/Wildlife/mammals/easternchipmunk.htm. Retrieved 2009-01-01.
- ^ "Florida Mouse". United States Fauna. http://www.unitedstatesfauna.com/floridamouse.php. Retrieved 2009-01-01.
- ^ "Brown Rat". Science Daily. http://www.sciencedaily.com/articles/b/brown_rat.htm. Retrieved 2009-01-01.
- ^ "Chimps on the Hunt". BBC. http://www.bbc.co.uk/nature/species/Common_Chimpanzee#p004hd8g. Retrieved 2010-03-23.
- ^ "Savanna Chimpanzees, Pan troglodytes verus, Hunt with Tools". Science Direct. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VRT-4N3XDTT-1&_user=10&_coverDate=03/06/2007&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=286aed913a0bc2720bb09d6333f8ebbc. Retrieved 2010-03-23.
- ^ Halle, S. & Stenseth, N. (2000). Activity patterns in small mammals: an ecological approach. Berlin; Heidelberg, Germany; New York: Springer-Verlag.
- ^ Singer, Michael S.; Bernays, Elizabeth A. (2003). "Understanding Omnivory Needs: A Behavioral Perspective". Ecology 84 (10): 2532–2537. doi:10.1890/02-0397.
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