Cannibalism

Three Mormon crickets eating a fourth Mormon cricket

In zoology, cannibalism is the act of one individual of a species consuming all or part of another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded for more than 1500 species^{[citation needed]} (this estimate is from 1981, and likely a gross underestimation).

Unlike previously believed, cannibalism is not just a result of extreme food shortage or artificial conditions, but commonly occurs under natural conditions in a variety of species.^[1][2][3] In fact, scientists have acknowledged that it is ubiquitous in natural communities. Cannibalism seems to be especially prevalent in aquatic communities, in which up to ~90% of the organisms engage in cannibalism at some point of the life cycle. Cannibalism is also not restricted to carnivorous species, but is commonly found in herbivores and detritivores.^[4]

Sexual cannibalism

Sexual cannibalism is a special case of cannibalism in which a female organism kills and consumes a conspecific (same species) male before, during, or after copulation. Rarely, these roles are reversed.^[5][6] Sexual cannibalism has been recorded in the female redback spider, black widow spider, praying mantis, and scorpion, among others.

Size structured cannibalism

Nematode Mononchidae eating another Mononchidae.

Size structured cannibalism, in which large individuals consume smaller conspecifics, is more common. In such size-structured populations, cannibalism can be responsible for 8% (Belding's Ground Squirrel) to 95% (dragonfly larvae) of the total mortality,^[7] making it a significant and important factor for population^[8] and community dynamics.^[9] Such size structured cannibalism has commonly been observed in the wild for a variety of taxa.

Cannibalistic infanticide

Another common form of cannibalism is filial cannibalism (a form of infanticide) where adults eat the young of their own species (sometimes even their own immediate offspring). Classical examples include the chimpanzees where groups of adult males have been observed to attack and consume conspecific infants,^[10][11][12] and cats,^[13] elephants, dogs, baboons, bears, lions,and some types of fish, where adult males commonly kill infants when they take over a new harem after replacing the previous dominant males.^[14][15] In agricultural settings, pigs are known to eat their own young, accounting for a sizeable percentage of total piglet deaths.

One, perhaps surprising, example is the bottlenose dolphin, which has been reported to kill its young through impact injuries.^[16] Another example is hamsters eating their young. Dominant male langurs tend to kill the existing young upon taking control of a harem.^[17] There has been sight of infanticide in the leopard population.^[18]

Particularly in fish, one can discern

• total filial cannibalism, where a parent eats the whole brood
• cases where a parent eats only part. E.g. sand gobies Potamoschistus minutus can eat 40% of their eggs without reducing the outcome of their reproductive efforts.^[19]

Intrauterine cannibalism

Intrauterine cannibalism is a behaviour in some carnivorous species, in which multiple embryos are created at impregnation, but only one or two are born. The larger or stronger ones consume their less-developed siblings as a source of nutrients.

In adelphophagy, the fetus eats sibling embryos, while in oophagy it feeds on eggs.^[20]

Intrauterine cannibalism is known to occur in lamnoid sharks^[21] and in the Fire Salamander,^[22] as well as in some teleost fishes.^[20] The Carboniferous-era chimaera, Delphyodontos dacriformes, is suspected of having practiced intrauterine cannibalism, also, due to the sharp teeth of the recently born (or possibly aborted) juveniles (adults are unknown), and the presence of fecal matter in the juveniles' guts.^[23]

References

Further reading

Wikimedia Commons has media related to: Animal cannibalism

• M. A. Elgar and Bernard J. Crespi (eds.). 1992. Cannibalism: Ecology and Evolution of Cannibalism among Diverse Taxa Oxford University Press, New York. (361pp) ISBN 0198546505

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