An omnivore , meaning 'all-eater', is an animal that can derive its energy and nutrients from
a diet consisting of a variety of food sources that may include plants, animals, algae, fungi
and select bacteria. Omnivores often are opportunistic, general
feeders which lack carnivore or herbivore specializations for acquiring or processing
food, but which nevertheless consume both animal protein and vegetation.
Word origins The word "omnivore" is a term of convenience,
and its significance varies according to the context of the type and degree of omnivory.
Traditionally the definition for omnivory relies on a species "including both animal
and vegetable tissue in the diet". The taxonomic utility of this definition is limited, since
the diet, behavior, and phylogeny of one omnivorous species might be very different from that
of another: for instance an omnivorous pig digging for roots and scavenging for fruit
and carrion is taxonomically and ecologically quite distinct from an omnivorous chameleon
that eats leaves and insects. The term "omnivory" is also not comprehensive because it does
not deal with mineral foods such as salt licks. Challenges for classifying
Though Carnivora is a taxon for species classification, no such equivalent exists for omnivores, as
omnivores are widespread across multiple taxonomic clades. Even the Carnivora order does not
include all carnivorous species, and not all species within the Carnivora taxon are carnivorous:
the eating of flesh is phylogenetically widespread. Many species are difficult to classify as
either omnivores, herbivores, or carnivores because few animals are strictly limited to
just one type of tissue in the diet. Even the cat and weasel families, usually regarded
as obligate carnivores, eat a little vegetable matter, for instance when they eat the guts
of prey, although this does not prove that they derive nutrition from it. Only certain
species like parasitoidal insects and insects that are specialist sap-suckers can be easily
classified based on their nutrient source. Another problem with classifying species as
omnivore, herbivore, or carnivore concerns changes in eating habits through an animal's
life cycle. Certain species, such as some grazing waterfowls like geese, are known to
eat mainly animal tissue at one stage of their lives, and plant matter at another. The same
is true for many insects, such as beetles in the family Meloidae, which begin by eating
animal tissue as larvae, but change to plant matter after they mature. Likewise, many mosquito
species begin with plants or assorted detritus. As they mature, however, the males continue
to eat plant matter and nectar, but the females, in addition to nectar, also eat blood in order
to reproduce effectively. Omnivorous species
Although cases exist of carnivores eating plant matter and 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 or the species as a whole omnivorous.
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 other categories, e.g. faunivore, folivore, and scavenger. Some researchers
argue that evolution of any species from herbivory to carnivory or carnivory to herbivory would
be rare except via an intermediate stage of omnivory.
Omnivorous species Various mammals are omnivorous in the wild,
such as the Hominidae, pigs, badgers, bears, coatis, hedgehogs, opossums, skunks, sloths,
squirrels, raccoons, chipmunks, mice, and rats. Various birds are omnivorous, with diets
varying from berries and nectar to insects, worms, fish, and small rodents. Examples include
cassowaries, chickens, crows and related corvids, keas, rallidae, and rheas. In addition, some
lizards, turtles, fish, and invertebrates are also omnivorous.
Most bear species are 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, and behaviorally.
Depending on the species of bear, there is generally a preference for one class of food,
as plants and animals are digested differently. Wolf subspecies have a general preference
and are evolutionarily geared towards meat, but also will voluntarily eat plant material
like fruits, vegetables, and grasses, and can live on such indefinitely. Also, the Maned
Wolf is a canid whose diet is naturally 50% plant matter.
While most mammals may display "omnivorous" behavior patterns depending on conditions
of supply, culture, season and so on, they will generally prefer a particular class of
food, to which their digestive processes are adapted. Like most arboreal species, most
squirrels are primarily granivores, subsisting on nuts and seeds. But like virtually all
mammals, squirrels avidly consume some animal food when it becomes available. For example,
the American Eastern gray squirrel has spread to parts of Britain, continental Europe and
South Africa. Where it flourishes, its effect on populations of nesting birds is often serious,
largely because of consumption of eggs and nestlings.
Other species Quite often, mainly herbivorous creatures
will eagerly eat small quantities of animal food when it becomes available. Although this
is trivial most of the time, omnivorous or herbivorous birds, such as sparrows, often
will feed their chicks insects while food is most needed for growth. On close inspection
it appears that nectar-feeding birds such as sunbirds rely on the ants and other insects
that they find in flowers, not for a richer supply of protein, but for essential nutrients
such as Cyanocobalamin that are absent from nectar. Similarly, monkeys of many species
eat maggoty fruit, sometimes in clear preference to sound fruit. When to refer to such animals
as omnivorous, or otherwise, is a question of context and emphasis, rather than of definition.
See also References
^ "Omnivore". National Geographic Education. National Geographic Society. Retrieved 4 October
2012. ^ McArdle, Ph.D., John. "Humans are Omnivores".
Vegetarian Journal. Retrieved 2 October 2012. ^ Collocott, T. C.. Chambers Dictionary of
science and technology. Edinburgh: W. and R. Chambers. ISBN 0-550-13202-3.
^ Ewer , R. F.. The Carnivores. London: Weidenfeld and Nicolson. ISBN 0-297-99564-2.
^ Maclean, Gordon Lindsay. Roberts' Birds of Southern Africa. Publisher: New Holland.
ISBN 978-0620175838. ^ Skaife, S. H.. African Insect Life. Pub.
Longmans, Green & Co., London. ^ Singer, Michael S.; Bernays, Elizabeth A..
"Understanding Omnivory Needs: A Behavioral Perspective". Ecology 84: 2532–2537. doi:10.1890/02-0397.
^ "Omnivores' ancestors primarily ate plants, or animals, but not both". Retrieved 17 April
2012. ^ http:www.npr.orgthesalt04150817741/for-most-of-human-history-being-an-omnivore-was-no-dilemma
^ Brent Huffman. "Family Suidae". UltimateUngulate.com. Retrieved 2007-12-29.
^ "Tree Squirrels". The Humane Society of the United States. Retrieved 2009-01-01.
^ "Eastern Chipmunk". Wonder Club. Retrieved 2009-01-01.
^ "Florida Mouse". United States Fauna. Retrieved 2009-01-01.
^ "Brown Rat". Science Daily. Retrieved 2009-01-01. ^ Seattle Audubon Society. "Family Corvidae".
BirdWeb.org. Retrieved 2011-01-01. ^ "Food and Diet". bearsmart.com. Retrieved
3 July 2013. ^ Halle, S. & Stenseth, N.. Activity patterns
in small mammals: an ecological approach. Berlin; Heidelberg, Germany; New York: Springer-Verlag.
p. 131. ^ Annex: Towards a Forestry Commission England
Grey Squirrel Policy, UK: Forestry Commission, 22 Jan 2006, retrieved 15 May 2012
^ Moller, H.. "Food and foraging behaviour of red and grey squirrels". Mammal Review
13: 81-98. ^ Capinera, John. Insects and Wildlife. Publisher:
Wiley-Blackwell. ISBN 978-1-4443-3300-8. ^ Ewing, Jack. Monkeys Are Made of Chocolate.
Publisher: Pixyjack Press. ISBN 978-0-9658098-1-8.