Cannibalism
Biology 342 Fall 06
Infanticide and Cannibalism
Infanticide
without cannibalism is a behavior that has been widely described in
numerous species (Glass 1985). Infanticide with cannibalism is
considerably more rare but far from unheard of, having been reported in
species such as lions, polar bears, and gulls (Elgar and Crespi, 331,
279).
Two major benefits of infanticide have been suggested: increased
nutrition and increased mating opportunities. In some amphibians, a
cannibalistic diet has been associated with accelerated growth and
higher survivorship (Elgar and Crespi 265). In times of food shortage,
cannibalism may be the best option to ensure survival to the next
reproduction. In the case of cannibalism of one's own offspring,
increasing the nutrition of the parent may be an investment towards
increasing future reproduction, at the cost of the current brood
(Filial cannibalism is discussed in more detail in the section on oophagy). In some species, evidence exists that
killing a female's current offspring can make her sexually receptive
sooner than if she had raised those young (Glass, 1985). Lions and
chimpanzees, for example, have been observed to kill juveniles and then
mate with their mother (The Lion Research Center, Elgar and Crespi 331). The synthesis
of these two explanations may help to account for situations in which
infanticide is followed by cannibalism. (For a video of male lion committing infanticide: http://www.lionresearch.org/behavior_guide/infant.html ).
Oophagy and infanticide have been recorded in Color-banded Ring-billed gulls. Both males and females
have been observed consuming eggs or trespassing chicks of conspecifics, although it is more
prevalent in males. Observations made by Brown and Lang showed
that all cannibalized chicks brought to the nest were alive on arrival (1996).
One dead chick was brought back to the nest but it was not eaten. They
were also seen eating unguarded eggs at an adjacent nest. The results
of Brown and Lang suggest that the only real selective advantage that
could be gained by this behavior is the elimination of competitor
genes, and even then it is a small contribution. Despite the lack of
any large fitness advantage, cannibalism in these birds is prevalent,
being the major cause of nest failure in some circumstances such as
failed breeders and food shortages. Twenty to forty percent of the
males observed in this study had cannibalistic behavior. Thus, these
authors and previous researchers propose that most cannibalism events
are carried out by only a few individuals with specialized behavior.
(Brown and Lang, 1996)
Two major benefits of infanticide have been suggested: increased
nutrition and increased mating opportunities. In some amphibians, a
cannibalistic diet has been associated with accelerated growth and
higher survivorship (Elgar and Crespi 265). In times of food shortage,
cannibalism may be the best option to ensure survival to the next
reproduction. In the case of cannibalism of one's own offspring,
increasing the nutrition of the parent may be an investment towards
increasing future reproduction, at the cost of the current brood
(Filial cannibalism is discussed in more detail in the section on oophagy). In some species, evidence exists that
killing a female's current offspring can make her sexually receptive
sooner than if she had raised those young (Glass, 1985). Lions and
chimpanzees, for example, have been observed to kill juveniles and then
mate with their mother (The Lion Research Center, Elgar and Crespi 331). The synthesis
of these two explanations may help to account for situations in which
infanticide is followed by cannibalism. (For a video of male lion committing infanticide: http://www.lionresearch.org/behavior_guide/infant.html ).Oophagy and infanticide have been recorded in Color-banded Ring-billed gulls. Both males and females
have been observed consuming eggs or trespassing chicks of conspecifics, although it is more
prevalent in males. Observations made by Brown and Lang showed
that all cannibalized chicks brought to the nest were alive on arrival (1996).
One dead chick was brought back to the nest but it was not eaten. They
were also seen eating unguarded eggs at an adjacent nest. The results
of Brown and Lang suggest that the only real selective advantage that
could be gained by this behavior is the elimination of competitor
genes, and even then it is a small contribution. Despite the lack of
any large fitness advantage, cannibalism in these birds is prevalent,
being the major cause of nest failure in some circumstances such as
failed breeders and food shortages. Twenty to forty percent of the
males observed in this study had cannibalistic behavior. Thus, these
authors and previous researchers propose that most cannibalism events
are carried out by only a few individuals with specialized behavior.
(Brown and Lang, 1996)