Cannibalism
[2] The rate of cannibalism increases in nutritionally poor environments as individuals turn to members of their own species as an additional food source.
[3] 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.
This would, in turn, increase the survival rate of the cannibal and thus provide an evolutionary advantage in environments where food is scarce.
[9] For example, female Fletcher's frogs lay their eggs in ephemeral pools that lack food resources.
Therefore, in order to survive, tadpoles within the same clutch are forced to consume each other and exploit their conspecifics as the only available source of nutrition.
A study conducted on another amphibian, the wood frog, tadpoles showed that those that exhibited cannibalistic tendencies had faster growth rates and higher fitness levels than non-cannibals.
[15] 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.
[11] Hence, predators normally partake in a cannibalistic diet in conditions where alternative food sources are absent or not as readily available.
Failure to recognize kin prey is also a disadvantage, provided cannibals target and consume younger individuals.
[16] The act of cannibalism may also facilitate trophic disease transmission within a population, though cannibalistically spread pathogens and parasites generally employ alternative modes of infection.
[4] This disease was prevalent in Papua New Guinea where tribes practiced endocannibalism in cannibalistic funeral rituals and consume the brains infected by these prions.
As resources dwindle, individuals are forced to change their behaviour which may lead to animal migration,[20] confrontation, or cannibalism.
[3] This is because the encounter rate between predator and prey increases, making cannibalism more convenient and beneficial than foraging within the environment.
Over time, the dynamics within the population change as those with cannibalistic tendencies may receive additional nutritional benefits and increase the size ratio of predator to prey.
[26] Hence, species such as the male dark fishing spider of the family Dolomedes self-sacrifice and spontaneously die during copulation to facilitate their own consumption by the female, thereby increasing the chance of survivorship of future offspring.
Vertebrate examples include pigs, where cannibalistic piglet savaging occurs at a rate of about 0.3% and is considered to be an abnormal behavior.
However, consumption by the sow of already dead piglets that were stillborn or accidentally crushed occurs at a much higher rate and is considered normal.
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.
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.
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,[42] the negative effects of accumulating embryo waste,[43] and predation.
[43] In some species of eusocial wasps, such as Polistes chinensis, the reproducing female will kill and feed younger larvae to her older brood.
Shifting their morphology plays a key role in their survival, creating bulkier bodies when put into environments where more developed tadpoles were present, to make it difficult for the individuals to swallow them whole.
