What are the Feeding Behaviors of Cannibals?
Posted August 3, 1998
Cannibalism, eating another of the same species, is a gruesome thought. Yet, it seems that cannibalism can have many survival advantages. Organisms of the same species
share the same habitat and the same niche. It would seem that these organisms have many chances to eat each other. Indeed their next meal would be close and very nutritious for them
since it would contain the correct proportion of amino acids and fats. As populations increase, competition for resources becomes more intense. When a cannibal eats its neighbor, it
has a nutritious meal and reduces competition.
Despite these potential benefits, cannibalism is rather rare. This suggests there may be negative consequences when organisms eat members of the same species. A truly
cannibalistic species would be in danger of eating themselves to extinction. Perhaps that is why cannibalism usually is limited to a few individuals or to a few episodes in the life
cycle of an organism.
For example the larvae of the tiger salamander sometimes become cannibals. When the density of these aquatic larvae increases, some change in appearance and behavior.
They get bigger heads, different teeth and eat their neighbors. The result is faster growth and earlier metamorphosis than the normal larvae. A recent study found these cannibal larvae
are more likely to eat unrelated individuals than their kin. However, when experimenters covered the nares, structures that enable the larvae to smell, the cannibalistic larvae consumed
relatives as often as others.
Another problem of cannibalism, discovered by researchers, is the transmission of disease. They hypothesized that an organism's chances of getting a disease
increased when eating the same species. Related organisms have genetically similar immune systems. If the sick relative couldn't fight off the disease, chances are the cannibal won't
be able to either. Therefore, eating a sick close relative is worse than eating a diseased unrelated organism. Deadly bacteria infect tiger salamander larvae. If tiger salamander larvae
eat infected individuals of the same species, they have a greater chance of dying then if they eat infected individuals of a different species.
Many types of fish in freshwater aquariums will eat their young as soon as they are born. Find out why this occurs. Find out what other animals act in this manner
and for what reasons.
Milius, S. "Why Aren't There More Cannibals Around?" Science News, 1998) Vol. 153, p. 295.
Pfennig, David W., Sherman, Paul W., & Collins, James P. "Kin Recognition and Cannibalism in Polyphenic Salamanders." Behavioral Ecology, (1994) Vol. 5 (2),
Reilly, Stephen M., Lauder, George V., & Collins, James P. "Performance Consequences of a Trophic Polymorphism: Feeding Behavior in Typical and Cannibal Phenotypes
of Ambystoma tigrinum." Copeia, (1992) Vol. 3, pp. 672-679.