Omnivore
An omnivore (
Omnivores come from diverse backgrounds that often independently evolved sophisticated consumption capabilities. For instance, dogs evolved from primarily
The variety of different animals that are classified as omnivores can be placed into further sub-categories depending on their
All of these animals are omnivores, yet still fall into special niches in terms of feeding behavior and preferred foods. Being omnivores gives these animals more food security in stressful times or makes possible living in less consistent environments.[18]
Etymology and definitions
The word omnivore derives from Latin omnis 'all' and vora, from vorare 'to eat or devour', having been coined by the French and later adopted by the English in the 1800s.[19] Traditionally the definition for omnivory was entirely behavioral by means of simply "including both animal and vegetable tissue in the diet.[20]" In more recent times, with the advent of advanced technological capabilities in fields like gastroenterology, biologists have formulated a standardized variation of omnivore used for labeling a species' actual ability to obtain energy and nutrients from materials.[21][22] This has subsequently conditioned two context-specific definitions.
- Behavioral: This definition is used to specify if a species or individual is actively consuming both plant and animal materials.[22][23][24][25] (e.g. "vegans do not participate in the omnivore based diet.") In the fields of nutrition, sociology and psychology the terms “omnivore” & “omnivory” is often used to distinguish prototypical highly diverse human diet patterns from restricted diet patterns that exclude major categories of food.[26][27][28][29][30]
- Physiological: This definition is often used in academia to specify species that have the capability to obtain energy and nutrients from both plant and animal matter.[31][page needed][6][21][32] (e.g. "humans are omnivores due to their capability to obtain energy and nutrients from both plant and animal materials.")
The taxonomic utility of omnivore's traditional and behavioral definition is limited, since the diet, behavior, and
Classification, contradictions and difficulties
Though Carnivora is a taxon for species classification, no such equivalent exists for omnivores, as omnivores are widespread across multiple taxonomic clades. The Carnivora order does not include all carnivorous species, and not all species within the Carnivora taxon are carnivorous. (The members of Carnivora are formally referred to as carnivorans.)[33] It is common to find physiological carnivores consuming materials from plants or physiological herbivores consuming material from animals, e.g. felines eating grass and deer eating birds.[34][35] From a behavioral aspect, this would make them omnivores, but from the physiological standpoint, this may be due to zoopharmacognosy. Physiologically, animals must be able to obtain both energy and nutrients from plant and animal materials to be considered omnivorous. Thus, such animals are still able to be classified as carnivores and herbivores when they are just obtaining nutrients from materials originating from sources that do not seemingly complement their classification. For instance, it is well documented that animals such as giraffes, camels, and cattle will gnaw on bones, preferably dry bones, for particular minerals and nutrients.[36] Felines, which are usually regarded as obligate carnivores, occasionally eat grass to regurgitate indigestibles (e.g. hair, bones), aid with hemoglobin production, and as a laxative.[37]
Occasionally, it is found that animals historically classified as carnivorous may deliberately eat plant material. For example, in 2013, it was considered that American alligators (Alligator mississippiensis) may be physiologically omnivorous once investigations had been conducted on why they occasionally eat fruits. It was suggested that alligators probably ate fruits both accidentally and deliberately.[38]
"Life-history omnivores" is a specialized classification given to organisms that change their eating habits during their life cycle.[39] Some species, such as grazing waterfowl like geese, are known to eat mainly animal tissue at one stage of their lives, but plant matter at another.[40] The same is true for many insects, such as beetles in the family Meloidae,[41] which begin by eating animal tissue as larvae, but change to eating plant matter after they mature. Likewise, many mosquito species in early life eat plants or assorted detritus, but as they mature, males continue to eat plant matter and nectar whereas the females (such as those of Anopheles, Aedes and Culex) also eat blood to reproduce effectively.[42]
Omnivorous species
General
Although cases exist of
Omnivorous mammals
Various mammals are omnivorous in the wild, such as species of hominids, pigs,[45] badgers, bears, foxes, coatis, civets, hedgehogs, opossums, skunks, sloths, squirrels,[46] raccoons, chipmunks,[47] mice,[48] hamsters and rats.[49][7][50][51]
Most bear species are omnivores,[52] but individual diets can range from almost exclusively herbivorous (hypocarnivore) to almost exclusively carnivorous (hypercarnivore), 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). Depending on the species of bear, there is generally a preference for one class of food, as plants and animals are digested differently. Canines including wolves, dogs, dingoes, and coyotes eat some plant matter, but they have a general preference and are evolutionarily geared towards meat.[53] However, the maned wolf is a canid whose diet is naturally 50% plant matter.
Like most arboreal species, squirrels are primarily granivores, subsisting on nuts and seeds.[54] However, like virtually all mammals, squirrels avidly consume some animal food when it becomes available. For example, the American eastern gray squirrel has been introduced to parts of Britain, continental Europe and South Africa. Its effect on populations of nesting birds is often serious because of consumption of eggs and nestlings.[55][56]
Other species
Various
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. When to refer to such animals as omnivorous, or otherwise, is a question of context and emphasis, rather than of definition.
See also
- Consumer-resource systems
- Evolution (biology)
- Food chain
- Food energy
- Ingestion
- List of diets
- Mesocarnivore
- Productivity (ecology)
- List of feeding behaviours
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