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. To consume the
same species or show cannibalism is a common ecological interaction in the
animal kingdom and has been recorded for more than 1,500 species. It does not, as
once believed, occur only as a result of extreme food shortages or artificial
conditions, but commonly occurs under natural conditions in a variety of
species. Cannibalism seems to be especially prevalent in aquatic
communities, in which up to approximately 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. Sexual cannibalism
Sexual cannibalism is a special case of cannibalism in which a female organism
kills and consumes a conspecific male before, during, or after copulation.
Rarely, these roles are reversed. 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 is cannibalism in which older, larger, more
mature individuals consume smaller, younger conspecifics. In size-structured
populations,, cannibalism can be responsible for 8% to 95% of the total
mortality, making it a significant and important factor for population and
community dynamics. Size-structured cannibalism has commonly
been observed in the wild for a variety of taxa. Vertebrate examples include
chimpanzees, where groups of adult males have been observed to attack and consume
infants. = Filial cannibalism=
Filial cannibalism is a specific type of size-structured cannibalism in which
adults eat their own offspring. Though most often thought of as parents eating
live young, filial cannibalism includes parental consumption of stillborn
infants and miscarried fetuses as well as infertile and still-incubating eggs.
Vertebrate examples include pigs, where savaging accounts for a sizable
percentage of total piglet deaths, and cats.
Filial cannibalism is particularly common in teleost fishes, appearing in
at least seventeen different families of teleosts. Within this diverse group of
fishes, there have been many, variable explanations of the possible adaptive
value of filial cannibalism. One of these is the energy-based hypothesis,
which suggests that fish eat their offspring when they are low on energy as
an investment in future reproductive success. This has been supported by
experimental evidence, showing that male three-spined sticklebacks, male
tessellated darters, and male sphinx blenny fish all consume or absorb their
own eggs to maintain their physical conditions. In other words, when males
of a fish species are low on energy, it might sometimes be beneficial for them
to feed on their own offspring to survive and invest in future
reproductive success. Another hypothesis as to the adaptive
value of filial cannibalism in teleosts is that it increases density-dependent
egg survivorship. In other words, filial cannibalism simply increases overall
reproductive success by helping the other eggs make it to maturity by
thinning out the numbers. Possible explanations as to why this is so
include increasing oxygen availability to the remaining eggs, the negative
effects of accumulating embryo waste, and predation.
In some species of eusocial wasps, such as P. chinensis, the reproducing female
will kill and feed younger larvae to her older brood. This occurs under food
stressed conditions in order to ensure that the first generation of workers
emerges without delay. Further evidence also suggests that occasionally filial
cannibalism might be the unfortunate by-product of cuckoldry in fish. Males
consume broods, which may include their own offspring, when they believe a
certain percentage of the brood contains genetic material that is not theirs.
The dinosaur Coelophysis was once suspected to have a degree in this form
of cannibalism but this turned out to be wrong, although Deinonychus may have
been. Skeletal remains from subadults with missing parts are suspected of
having been eaten by other Deinonychus, mainly full-grown adults.
= Infanticide= Infanticide is the killing of a
non-adult animal by an adult of the same species. Infanticide is often, but not
always, accompanied by cannibalism. It is often displayed in lions; a male lion
encroaching on the territory of a rival pride will often kill any existing cubs
fathered by other males; this brings the lionesses into heat more quickly,
enabling the invading lion to sire his own young. This is a good example of
cannibalistic behavior in a genetic context.
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 or embryophagy, the fetus eats sibling embryos, while in
oophagy it feeds on eggs. Adelphophagy occur in some marine
gastropods and in some marine annelids. Intrauterine cannibalism is known to
occur in lamnoid sharks such as the sand tiger shark, and in the Fire Salamander,
as well as in some teleost fishes. The Carboniferous period chimaera,
Delphyodontos dacriformes, is suspected of having practiced intrauterine
cannibalism, also, due to the sharp teeth of the recently born juveniles,
and the presence of fecal matter in the juveniles' intestines.
See also Cannibalism
References Further reading
M. A. Elgar and Bernard J. Crespi. 1992. Cannibalism: Ecology and Evolution of
Cannibalism among Diverse Taxa Oxford University Press, New York. ISBN
0-19-854650-5