Cannibalism (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

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 speciesfact|date=February 2008 (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 [G. A. Polis, The evolution and dynamics of intraspecific predation. Annual Review of Ecology and Systematics 12, 225-251 (1981).] . [Laurel R. Fox, Cannibalism in natural populations. Annual Review of Ecology and Systematics 6, 87-106 (1975).] [M. A. Elgar and B. J. (eds) Crespi, Cannibalism: Ecology and evolution among diverse taxa. (Oxford University Press, New York, 1992).] 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. [Laurel R. Fox, Cannibalism in natural populations. Annual Review of Ecology and Systematics 6, 87-106 (1975).]

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.cite web |url=http://ib.berkeley.edu/courses/ib160/past_papers/suttle.html |title=The Evolution of Sexual Cannibalism |author=Kenwyn Blake Suttle |year=1999 |publisher=University of California, Berkeley] cite journal |quotes=no |url=http://www.bioone.org/perlserv/?request=get-abstract&issn=0278-0372&volume=023&issue=03&page=0662 |title=Cannibalism within mating pairs of the parasitic isopod "Ichthyoxenus fushanensis" |author=Min-Li Tsai & Chang-Feng Dai |journal=Journal of Crustacean Biology |volume=23 |issue=3 |year=2003 |pages=662–668 |doi=10.1651/C-2343 |format=abstract page] Sexual cannibalism has been recorded in the female redback spider, black widow spider, praying mantis, and scorpion, among others.

Size structured cannibalism

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, [G. A. Polis, The evolution and dynamics of intraspecific predation. Annual Review of Ecology and Systematics 12, 225-251 (1981)] making it a significant and important factor for population [David Claessen, A. M. De Roos, and L. Persson, Population dynamic theory of size-dependent cannibalism. Proceedings of the Royal Society of London Series B-Biological Sciences 271 (1537), 333-340 (2004)] and community dynamics [V. H. W. Rudolf, Consequences of stage-structured predators: Cannibalism, behavioral effects and trophic cascades. Ecology 88, 2991-3003 (2007)] . 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 [A. C. Arcadi and R. W. Wrangham, Infanticide in chimpanzees: Review of cases and a new within-group observation from the Kanyawara study group in Kibale National Park. Primates 40 (2), 337-351 (1999).] , [M. L. Wilson, W. R. Wallauer, and A. E. Pusey, New cases of intergroup violence among chimpanzees in Gombe National Park, Tanzania. International Journal Of Primatology 25 (3), 523-549 (2004).] [D. P. Watts, J. C. Mitani, and H. M. Sherrow, New cases of inter-community infanticide by male chimpanzees at Ngogo, Kibale National Park, Uganda. Primates 43 (4), 263-270 (2002)] and cats [http://www.messybeast.com/kill_kit.htm] , 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 [C. Packer, Infanticide is no fallacy. American Anthropologist 102 (4), 829 (2001).] [B.C. Bertram, Social factors influencing reproduction in wild lions. Journal of Zoology 177, 463-482 (1975).] . 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. [Citation|last=Milius|first=S.|title=Infanticide Reported in Dolphins|periodical=Science News|volume=154|issue=3|pages=36|date=July 18, 1998|url= http://www.sciencenews.org/pages/sn_arc98/7_18_98/fob1.htm |accessdate=2007-05-22] Another example is hamsters eating their young. Dominant male langurs tend to kill the existing young upon taking control of a harem. [Citation|title=The evolution of infanticidal mechanisms in male langurs|url= http://mentor.lscf.ucsb.edu/course/fall/psyc155/langurs-j05.pdf |accessdate=2007-05-22] There has been sight of infanticide in the leopard population [Citation|last=Fildes|first=Jonathan|title=Cheating cheetahs caught by DNA|url=http://news.bbc.co.uk/2/hi/science/nature/6701515.stm |accessdate=2007-05-30] .

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. [ [http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1554%2F05-283.1&ct=1 Bioone Online Journals - Parents Benefit From Eating Offspring: Density-Dependent Egg Survivorship Compensates For Filial Cannibalism ] ]

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.cite journal | last = Crespi | first = Bernard | coauthors = Christina Semeniuk | title = Parent-Offspring Conflict in the Evolution of Vertebrate Reproductive Mode | journal = The American Naturalist | volume = 163 | issue = 5 | pages = 635–654 | date = 2004 | doi = 10.1086/382734 | id = ]

Intrauterine cannibalism is known to occur in lamnoid sharks [cite journal | last = Hamlett | first = William C. | coauthors = Allison M. Eulitt, Robert L. Jarrell, Matthew A. Kelly | title = Uterogestation and placentation in elasmobranchs | journal = Journal of Experimental Zoology | volume = 266 | issue = 5 | pages = 347–367 | date = 1993 | url = | doi = 10.1002/jez.1402660504 | id = | accessdate = ] and in the Fire Salamander, [cite book | last = Stebbins | first = Robert C. | authorlink = | coauthors = Nathan W. Cohen | title = A Natural History of Amphibians | publisher = Princeton University Press | date = 1995 | location = Princeton, NJ | pages = 9 | id = ISBN 0-69110-251-1 ] as well as in some teleost fishes. The Carboniferous 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. [Lund, R. 1980. Viviparity and intrauterine feeding in a new holocephalan fish from the Lower Carboniferous of Montana. Science, 209: 697‑699.]

References

Further reading

*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