Cannibalism

Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is well-documented, both in ancient and in recent times. Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is well-documented, both in ancient and in recent times. The rate of cannibalism increases in nutritionally-poor environments as individuals turn to conspecifics as an additional food-source. Cannibalism regulates population numbers, whereby resources such as food, shelter and territory become more readily available with the decrease of potential competition. Although it may benefit the individual, it has been shown that the presence of cannibalism decreases the expected survival rate of the whole population and increases the risk of consuming a relative. Other negative effects may include the increased risk of pathogen transmission as the encounter rate of hosts increases. Cannibalism, however, does not—as once believed—occur only as a result of extreme food shortage or of artificial/unnatural conditions, but may also occur under natural conditions in a variety of species. Cannibalism is prevalent in aquatic ecosystems, in which up to approximately 90% of the organisms engage in cannibalistic activity at some point in their life-cycle. Cannibalism is not restricted to carnivorous species: it also occurs in herbivores and in detritivores. Sexual cannibalism normally involves the consumption of the male by the female individual before, during or after copulation. Other forms of cannibalism include size-structured cannibalism and intrauterine cannibalism. Behavioural, physiological and morphological adaptations have evolved to decrease the rate of cannibalism in individual species. In environments where food availability is constrained, individuals can receive extra nutrition and energy if they use other conspecific individuals as an additional food source. This would, in turn, increase the survival rate of the cannibal and thus provide an evolutionary advantage in environments where food is scarce. A study conducted on wood frog tadpoles showed that those that exhibited cannibalistic tendencies had faster growth rates and higher fitness levels than non-cannibals. An increase of size and growth would give them the added benefit of protection from potential predators such as other cannibals and give them an advantage when competing for resources The nutritional benefits of cannibalism may allow for the more efficient conversion of a conspecific diet into reusable resources than fully herbaceous diet; as herbaceous diets may consist of excess elements which the animal has to expend energy to get rid of. This facilitates for faster development; however, a trade-off may occur as there may be less time to ingest these acquired resources. Studies have shown that there is a noticeable size difference between animals fed on a high conspecific diet which were smaller compared to those fed on a low conspecific diet. Hence, individual fitness could only be increased if the balance between developmental rate and size is balanced out, with studies showing that this is achieved in low conspecific diets. Cannibalism regulates population numbers and benefits the cannibalistic individual and its kin as resources such as extra shelter, territory and food are freed; thereby increasing the fitness of the cannibal; by lowering crowding effects. However, this is only the case if the cannibal recognizes its own kin as this won't hinder any future chances of perpetuating its genes in future generations. The elimination of competition can also increase mating opportunities, allowing further spread of an individual's genes. Animals which have diets consisting of predominantly conspecific prey expose themselves to a greater risk of injury and expend more energy foraging for suitable prey as compared to non-cannibalistic species. In order to combat the risk of personal injury, a predator often targets younger or more vulnerable prey. However, the time necessitated by such selective predation could result in a failure to meet the predator's self-set nutritional requirements. In addition, the consumption of conspecific prey may also involve the ingestion of defense compounds and hormones, which have the capacity to impact the developmental growth of the cannibal's offspring. Hence, predators normally partake in a cannibalistic diet in conditions where alternative food sources are absent or not as readily available.