Cannibalism: The Facts

What is Cannibalism?

Cannibalism is defined as "the killing or consumption of either all or part of an individual that is of the same species" (Elgar and Crespi 2).  A number of factors, both ecological and social, contribute to the occurrence of cannibalism. Variables such as availability of alternative food, population density, and competition combine to produce favorable conditions for cannibalism, even when the potential costs of such behavior are significant.Remains of polar bears killed for food (Amstrup).

Cannibalism has been described across a wide spread of taxonomic groups, in numerous species from cilia to chimpanzees. For some species, cannibalism is a rare event, limited to times of extreme food shortage (as is hypothesized for polar bears, Amstrup 2006), in others it is a normal  mechanism of food acquisition (eg. sibling cannibalism in some beetle larvae, Elgar and Crespi 161).

Who eats who?

For the most part, cannibalism occurs when the victim is smaller or otherwise more vulnerable than the cannibal. Juvenile animals have been observed cannibalizing eggs or other juveniles, and adult animals have been observed cannibalizing eggs, juveniles, and rarely, other adults. Some organisms have even evolved to produce so-called "trophic eggs" that are un-viable, and appear to be "destined to be cannibalized" (Elgar and Crespi 176). 

Contexts for cannibalism

Cannibalism has been observed in a wide variety of contexts. This website will explore four broad categories of cannibalism: sexual cannibalism, oophagy/embryophagy, competitive cannibalism, and juvenile cannibalism. While we cannot possibly discuss all of the species in which these behaviors have been observed, we will highlight a few representative examples, and describe the general mechanism, adaptive value, and phylogenetic relationships for each category.