A slug, Arion vulgaris, eating a dead individual of the same species
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.[1]Human cannibalism is also well documented, both in ancient and in recent times.[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.[3] Other negative effects may include the increased risk of pathogen transmission as the encounter rate of hosts increases.[4] 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.[1][5][6]
At the ecosystem level, cannibalism is most common in aquatic settings, with a cannibalism rate of up to 0.3% amongst fish.[7][8] Cannibalism is not restricted to carnivorous species: it also occurs in herbivores and in detritivores.[vague][5]Sexual cannibalism normally involves the consumption of the male by the female individual before, during or after copulation.[3] Other forms of cannibalism include size-structured cannibalism and intrauterine cannibalism. Behavioral, physiological and morphological adaptations have evolved to decrease the rate of cannibalism in individual species.[3]
Benefits
In environments where food availability is constrained, individuals can receive extra nutrition and energy if they use members of their own species, also known as conspecifics, 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.[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.[10] 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.[3]
The nutritional benefits of cannibalism may allow for the more efficient conversion of a conspecific diet into reusable resources than a fully herbaceous diet; as herbaceous diets may consist of excess elements which the animal has to expend energy to get rid of.[11] This facilitates 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.[11] 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.[11]
In some insects, cannibalism is used to control population. In confused flour beetles, population density is lowered by cannibalism when crowding occurs.[12]
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[9] by lowering crowding effects. However, this is only the case if the cannibal recognizes its own kin as this will not 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.[13]
Costs
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.[3]
Predators often target younger or more vulnerable prey.[14] However, the time necessitated by such selective predation could result in a failure to meet the predator's self-set nutritional requirements.[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. For example, a male stickleback fish may often mistake their own "eggs" for their competitor's eggs, and hence would inadvertently eliminate some of its own genes from the available gene pool.[3]Kin recognition has been observed in tadpoles of the spadefoot toad, whereby cannibalistic tadpoles of the same clutch tended to avoid consuming and harming siblings, while eating other non-siblings.[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]
Diseases transmitted through cannibalism
Cannibalism can potentially reduce the prevalence of parasites in the population by decreasing the number of susceptible hosts and indirectly killing the parasite in the host.[17] It has been shown in some studies that the risk of encountering an infected victim increases when there is a higher cannibalism rate, though this risk drops as the number of available hosts decreases.[17] However, this is only the case if the risk of disease transmission is low.[4] Cannibalism is an ineffective method of disease spread as cannibalism in the animal kingdom is normally a one-on-one interaction, and the spread of disease requires group cannibalism; thereby it is rare for a disease to have evolved to rely solely on cannibalism to spread. Usually there are different means of transmission, such as with direct contact, maternal transmission, coprophagy, and necrophagy with different species.[4] Infected individuals are more likely to be consumed than non-infected individuals, thus some research has suggested that the spread of disease may be a limiting factor to the prevalence of cannibalism in the population.[17]
Some examples of diseases transmitted by cannibalism in mammals include the human disease Kuru which is a prion disease that degenerates the brain.[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.[18] It is a cerebellar dysfunctional disease which has symptoms including a broad-based gait and decreased motor activity control; however, the disease has a long incubation period and symptoms may not appear until years later.[18]
Bovine spongiform encephalopathy, or mad cow disease is another prion disease which is usually caused by feeding contaminated bovine tissue to other cattle.[19] It is a neurodegenerative disease and could be spread to humans if the individual were to consume contaminated beef. The spread of parasites such as nematodes may also be facilitated by cannibalism as eggs from these parasites are transferred more easily from one host to another.[4]
Cannibalism may become apparent when direct competition for limited resources forces individuals to use other conspecific individuals as an additional resource to maintain their metabolic rates.[3] Hunger drives individuals to increase their foraging rates, which in turn decreases their attack threshold and tolerance to other conspecific individuals. As resources dwindle, individuals are forced to change their behaviour which may lead to animal migration,[20] confrontation, or cannibalism.[3]
Cannibalism rates increase with increasing population density as it becomes more advantageous to prey on conspecific organisms than to forage in the environment.[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.[21] The presence of smaller prey, or prey which are at a vulnerable stage of their life cycle, increases the chances of cannibalism occurring due to the reduced risk of injury.[22] A feedback loop occurs when increasing rates of cannibalism decreases population densities, leading to an increased abundance of alternative food sources; making it more beneficial to forage within the environment than for cannibalism to occur.[3] When population numbers and foraging rates increase, the carrying capacity for that resource in the area may be reached, thus forcing individuals to look for other resources such as conspecific prey.
Sexual cannibalism is present largely in spiders and other invertebrates, including gastropods.[3] This refers to the killing and consumption of conspecific sexual partners during courtship, and during or after copulation. Normally, it is the female which consumes the conspecific male organism, though there have been some reported cases of the male consuming the adult female, however, this has only been recorded under laboratory conditions.[3][23][24] Sexual cannibalism has been recorded in the female redback spider, black widow spider, praying mantis, and scorpion, among others.
In most species of spiders, the consumption of the male individual occurs before copulation and the male fails to transfer his sperm into the female.[3] This may be due to mistaken identity such as in the case of the orb weaving spider which holds little tolerance to any spider which is present in its web and may mistake the vibrations for those of a prey item.[3] Other reasons for male consumption before mating may include female choice and the nutritional advantages of cannibalism.[25] The size of the male spider may play a part in determining its reproductive success as smaller males are less likely to be consumed during pre-copulation; however, larger males may be able to prevent the smaller ones from gaining access to the female.[25] There exists a conflict of interest between males and females, as females may be more inclined to turn to cannibalism as a source of nutritional intake while the male's interest is mostly focused on ensuring paternity of the future generations.[3] It was found that cannibalistic females produced offspring with greater survival rates than non-cannibalistic females, as cannibals produced greater clutches and larger egg sizes.[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.[27]
Sexual dimorphism has been theorised to have arisen from sexual selection as smaller males were captured more easily than larger males; however, it is also possible that sexual cannibalism only occurs due to the difference in size between male and females.[3] Data comparing female and male spider body length shows that there is little support for the prior theory as there is not much correlation between body size and the presence of sexual cannibalism. Not all species of spiders which partake in sexual cannibalism exhibit size dimorphism.[3]
The avoidance of sexual cannibalism is present in males of certain species to increase their rate of survival, whereby the male uses cautionary methods to lower the risk of his consumption.[3] Male orb weaving spiders would often wait for females to moult or to finish eating before attempting to initiate mating, as the females are less likely to attack.[3] Males which are vulnerable to post-copulation consumption may gather mating thread to generate a mechanical tension which they could use to spring away after insemination, while other spiders such as the crab spider may tangle the female's legs in webs to reduce the risk of the female capturing him.[3] Male choice is common in mantids whereby males were observed to choose fatter females due to the reduced risk of attack and were more hesitant to approach starved females.[28]
Size-structured cannibalism is cannibalism in which older, larger, more mature individuals consume smaller, younger conspecifics. In size-structured populations, (where populations are made of individuals of various sizes, ages, and maturities), cannibalism can be responsible for 8% (Belding's ground squirrel) to 95% (dragonflylarvae) of the total mortality,[1] making it a significant and important factor for population[29] and community dynamics.[30]
Size-structured cannibalism has commonly been observed in the wild for a variety of taxa. Vertebrate examples include chimpanzees, where groups of adult males have been observed to attack and consume infants.[31][32][33]
Filial cannibalism is a specific type of size-structured cannibalism in which adults eat their own offspring.[34] Although most often thought of as parents eating live young, filial cannibalism includes parental consumption of stillborn infants and miscarried fetuses as well as infertile and still-incubating eggs. 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.[35][36]
Filial cannibalism is particularly common in teleost fishes, appearing in at least seventeen different families of teleosts.[37] Within this diverse group of fish, there have been many, variable explanations of the possible adaptive value of filial cannibalism. 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.[34] This has been supported by experimental evidence, showing that male three-spined sticklebacks,[34][38][39] male tessellated darters,[40] and male sphinx blenny fish[41] all consume or absorb their own eggs to maintain their physical conditions. 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.
Another hypothesis as to the adaptive value of filial cannibalism in teleosts is that it increases density-dependent egg survivorship. 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. This occurs under food stressed conditions in order to ensure that the first generation of workers emerges without delay.[44] Further evidence also suggests that occasionally filial cannibalism might occur as a by-product of cuckoldry in fish. Males consume broods, which may include their own offspring, when they believe a certain percentage of the brood contains genetic material that is not theirs.[38][45]
It is not always the parent that cannibalizes the offspring; in some spiders, mothers have been observed to feed themselves to their brood as the ultimate provision from mother to children, known as matriphagy.[46]
The dinosaurCoelophysis was once suspected to practice this form of cannibalism but this turned out to be wrong, although Deinonychus may have done so. Skeletal remains from subadults with missing parts are suspected of having been eaten by other Deinonychus, mainly full-grown adults.
Infanticide is the killing of a non-adult animal by an adult of the same species. Infanticide is often accompanied by cannibalism. It is often displayed in lions; a male lion encroaching on the territory of a rival pride will often kill any existing cubs fathered by other males; this brings the lionesses into heat more quickly, enabling the invading lion to sire his own young. This is an example of cannibalistic behaviour in a genetic context.
In many species of Lepidoptera, such as Cupido minimus and the Indianmeal moth, the first larvae to hatch will consume the other eggs or smaller larvae on the host plant, decreasing competition.[47][48]
Intrauterine cannibalism is a behaviour in some carnivorous species, in which multiple embryos are created at impregnation, but only one or two are born. The larger or stronger ones consume their less-developed siblings as a source of nutrients.
In adelphophagy or embryophagy, the fetus eats sibling embryos, while in oophagy it feeds on eggs.[49][50]
Intrauterine cannibalism is known to occur in lamnoid sharks[52] such as the sand tiger shark, and in the fire salamander,[53] as well as in some teleost fishes.[50] The Carboniferous period chimaera, Delphyodontos dacriformes, is suspected of having practiced intrauterine cannibalism, also, due to the sharp teeth of the recently born (or possibly aborted) juveniles, and the presence of fecal matter in the juveniles' intestines.[54]
Protection against cannibalism
Animals have evolved protection to prevent and deter potential predators such as those from their own kind.[3] Many amphibian eggs are gelatinous and toxic to decrease edibility. Often, adults would lay their eggs in crevices, holes, or empty nesting sites to hide their eggs from potential conspecific predators which tend to ingest the eggs for an additional nutritional benefit or to get rid of genetic competition. In amphibians, the development of non-aquatic egg deposition has helped increase the survival rates of their young by the evolution of viviparity or direct development.[3] In bees, worker policing occurs to prohibit worker reproduction, whereby workers cannibalize other worker laid eggs.[55] Queen laid eggs have a different scent than worker laid eggs, allowing workers to differentiate between the two, allowing them to nurture and protect queen laid eggs rather than cannibalising them.[55] Parental presence at nesting sites is also a common method of protection against infanticide committed by conspecific individuals, whereby the parent exhibits defensive displays to ward off potential predators. Parental investment in newborns are generally higher during their early stages of development whereby behaviours such as aggression, territorial behaviour, and pregnancy blocking become more apparent.[3]
Morphological plasticity helps an individual account for different predation stresses, thereby increasing individual survival rates.[56] Japanese brown frog tadpoles have been shown to exhibit morphological plasticity when they are in a high stress environment where cannibalism between tadpoles and more developed individuals were present. 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.[56] Diet shifts between different stages of development have also evolved to decrease competition between each stage, thereby increasing the amount of food availability so that there is a decreased chance that the individuals will turn to cannibalism as an additional food source.[3]
Poison dart frog is the common name of a group of frogs in the family Dendrobatidae which are native to tropical Central and South America. These species are diurnal and often have brightly colored bodies. This bright coloration is correlated with the toxicity of the species, making them aposematic. Some species of the family Dendrobatidae exhibit extremely bright coloration along with high toxicity — a feature derived from their diet of ants, mites and termites— while species which eat a much larger variety of prey have cryptic coloration with minimal to no amount of observed toxicity. Many species of this family are threatened due to human infrastructure encroaching on their habitats.
Argiope keyserlingi is a species of orb-web spider found on the east coast of Australia, from Victoria to northern Queensland. It is very similar in appearance to a closely related north Queensland species, Argiope aetherea. A. keyserlingi is commonly found in large populations in suburban parks and gardens, particularly among the leaves of Lomandra longifolia. Like many species of orb-web spiders, A. keyserlingi shows considerable sexual dimorphism, with the females being many times larger than the males. Mature females can be seen during the summer, and seeing multiple males on the web of one female is not uncommon.
Argiope bruennichi, commonly known as the wasp spider, is a species of orb-weaver spider found across Central and Northern Europe, several regions of Asia, plus parts of the Middle east, North Africa and the Azores. Like many other members of the same genus Argiope, this species features distinctive yellow, white and black markings on its abdomen.
Latrodectus hesperus, the western black widow spider or western widow, is a venomous spider species found in western regions of North America. The female's body is 14–16 mm in length and is black, often with an hourglass-shaped red mark on the lower abdomen. This "hourglass" mark can be yellow, and on rare occasions, white. The male of the species is around half this length and generally a tan color with lighter striping on the abdomen. The population was previously described as a subspecies of Latrodectus mactans and it is closely related to the northern species Latrodectus variolus. The species, as with others of the genus, build irregular or "messy" webs: unlike the spiral webs or the tunnel-shaped webs of other spiders, the strands of a Latrodectus web have no apparent organization.
Misumena vatia is a species of crab spider with a holarctic distribution. In North America, it is called the goldenrod crab spider or flower (crab) spider, as it is commonly found hunting in goldenrod sprays and milkweed plants. They are called crab spiders because of their unique ability to walk sideways as well as forwards and backwards. Both males and females of this species progress through several molts before reaching their adult sizes, though females must molt more to reach their larger size. Females can grow up to 10 mm (0.39 in) while males are quite small, reaching 5 mm (0.20 in) at most. Misumena vatia are usually yellow or white or a pattern of these two colors. They may also present with pale green or pink instead of yellow, again, in a pattern with white. They have the ability to change between these colors based on their surroundings through the molting process. They have a complex visual system, with eight eyes, that they rely on for prey capture and for their color-changing abilities. Sometimes, if Misumena vatia consumes colored prey, the spider itself will take on that color.
Spider cannibalism is the act of a spider consuming all or part of another individual of the same species as food. It is most commonly seen as an example of female sexual cannibalism where a female spider kills and eats a male before, during, or after copulation. Cases of non-sexual cannibalism or male cannibalism of females both occur but are notably rare.
Sexual cannibalism is when an animal, usually the female, cannibalizes its mate prior to, during, or after copulation. This trait is observed in many arachnid orders, several insect and crustacean clades, gastropods, and some snake species. Several hypotheses to explain this seemingly paradoxical behavior have been proposed, including the adaptive foraging hypothesis, aggressive spillover hypothesis and mistaken identity hypothesis. This behavior is believed to have evolved as a manifestation of sexual conflict, occurring when the reproductive interests of males and females differ. In many species that exhibit sexual cannibalism, the female consumes the male upon detection. Females of cannibalistic species are generally hostile and unwilling to mate; thus many males of these species have developed adaptive behaviors to counteract female aggression.
The scissortail sergeant or striptailed damselfish is a large damselfish. It earns its name from the black-striped tail and sides, which are reminiscent of the insignia of a military Sergeant, being similar to those of the sergeant major damselfish. It grows to a length of about 16 centimetres (6.3 in).
In animals, infanticide involves the intentional killing of young offspring by a mature animal of the same species. Animal infanticide is studied in zoology, specifically in the field of ethology. Ovicide is the analogous destruction of eggs. The practice has been observed in many species throughout the animal kingdom, especially primates but including microscopic rotifers, insects, fish, amphibians, birds and mammals. Infanticide can be practiced by both males and females.
The Ezo salamander, also known as the Hokkaido salamander, Noboribetsu salamander, or Ezo Sanshouo in Japanese is a species of salamander in the family Hynobiidae. Prior to 1923 the species was also classified by the binomial scientific name Satobius retardatus. H. retardatus is endemic to Japan's northernmost prefecture, the island of Hokkaido. The species is a pond-type salamander, and its natural habitats are temperate forests, temperate shrubland, swamps, freshwater marshes, intermittent freshwater marshes, freshwater springs, irrigated land, canals, and ditches.
Utetheisa ornatrix, also called the ornate bella moth, ornate moth, bella moth or rattlebox moth, is a moth of the subfamily Arctiinae. It is aposematically colored ranging from pink, red, orange and yellow to white coloration with black markings arranged in varying patterns on its wings. It has a wingspan of 33–46 mm. Moths reside in temperate midwestern and eastern North America as well as throughout Mexico and other parts of Central America. Unlike most moths, the bella moth is diurnal. Formerly, the bella moth or beautiful utetheisa of temperate eastern North America was separated as Utetheisa bella. Now it is united with the bella moth in Utetheisa ornatrix.
The six-spotted fishing spider is an arachnid from the nursery web spider family Pisauridae. This species is from the genus Dolomedes, or the fishing spiders. Found in wetland habitats throughout North America, these spiders are usually seen scampering along the surface of ponds and other bodies of water. They are also referred to as dock spiders because they can sometimes be witnessed quickly vanishing through the cracks of boat docks. D. triton gets its scientific name from the Greek mythological god Triton, who is the messenger of the big sea and the son of Poseidon.
Ranitomeya variabilis, formerly known as Dendrodates variabilis, is a species of small poison dart frog distributed in northern Peru, along the eastern slope of Andes in the upper Rio Huallaga drainage basin. Its common name, Zimmerman's poison frog, is named after Elke Zimmermann, a German zoologist who described the morph of this species and differentiated it from D. ventrimaculatus. The species was formerly considered to be synonymous with Ranitomeya ventrimaculata.
Filial cannibalism occurs when an adult individual of a species consumes all or part of the young of its own species or immediate offspring. Filial cannibalism occurs in many species ranging from mammals to insects, and is especially prevalent in various types of fish species with males that engage in egg guardianship. The exact evolutionary purpose of the practice in those species is unclear and debated among zoologists, though there is consensus that it may have, or may have had at some point in species' evolutionary history, certain evolutionary and ecological implications.
Pisaurina mira, also known as the American nursery web spider, due to the web it raises young in, is a species of spider in the family Pisauridae. They are often mistaken for wolf spiders (Lycosidae) due to their physical resemblance. P. mira is distinguished by its unique eye arrangement of two rows.
Matriphagy is the consumption of the mother by her offspring. The behavior generally takes place within the first few weeks of life and has been documented in some species of insects, nematode worms, pseudoscorpions, and other arachnids as well as in caecilian amphibians.
Agelenopsis pennsylvanica, commonly known as the Pennsylvania funnel-web spider or the Pennsylvania grass spider, is a species of spider in the family Agelenidae. The common name comes from the place that it was described, Pennsylvania, and the funnel shape of its web. Its closest relative is Agelenopsis potteri.
Argiope radon is a species of orb web spider native to Australia. It is found in tropical areas of the Northern Territory, Western Australia and Queensland. It is commonly known as the Northern St Andrew's cross spider.
Pardosa agrestis is a non-web-building spider in the family Lycosidae, commonly known as wolf spiders.
Pardosa pseudoannulata, a member of a group of species referred to as wolf-spiders, is a non-web-building spider belonging to the family Lycosidae. P. pseudoannulata are wandering spiders that track and ambush prey and display sexual cannibalism. They are commonly encountered in farmlands across China and other East Asian countries. Their venom has properties that helps it function as an effective insecticide, and it is, therefore, a crucial pesticide control agent.
↑ Elgar, M. A. and Crespi, B. J. (eds) (1992) Cannibalism: Ecology and evolution among diverse taxa. Oxford University Press, New York.[ISBNmissing][pageneeded]
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↑ Mahfoud, Nawal & Kafu, Ali & Maghrabi, Hassan. (2016). Study of the Cannibalistic Cohorts Among the Various Life Stages of Confused Flour Beetle Tribolium confusum DuVal (Coleoptera: Tenebrionidae) Under Laboratory Conditions. 19. 11–27.
↑ Pfennig, David W.; Reeve, Hudson K.; Sherman, Paul W. (1993). "Kin recognition and cannibalism in spadefoot toad tadpoles". Animal Behaviour. 46: 87–94. doi:10.1006/anbe.1993.1164. S2CID53175714.
↑ Finberg, Karin E. (2004). "Mad cow disease in the United States: An update on bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease". Clinical Microbiology Newsletter. 26 (15): 113–118. doi:10.1016/j.clinmicnews.2004.07.001.
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↑ Arcadi, Adam Clark; Wrangham, Richard W. (1999). "Infanticide in chimpanzees: Review of cases and a new within-group observation from the Kanyawara study group in Kibale National Park". Primates. 40 (2): 337–351. doi:10.1007/BF02557557. S2CID24050100.
↑ Wilson, Michael L.; Wallauer, William R.; Pusey, Anne E. (2004). "New Cases of Intergroup Violence Among Chimpanzees in Gombe National Park, Tanzania". International Journal of Primatology. 25 (3): 523–549. doi:10.1023/B:IJOP.0000023574.38219.92. S2CID9354530.
↑ Watts, David P.; Sherrow, Hogan M.; Mitani, John C. (2002). "New cases of inter-community infanticide by Male Chimpanzees at Ngogo, Kibale National Park, Uganda". Primates. 43 (4): 263–270. doi:10.1007/BF02629601. PMID12426461. S2CID7621558.
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M. A. Elgar and Bernard J. Crespi (eds.). 1992. Cannibalism: Ecology and Evolution of Cannibalism among Diverse Taxa Oxford University Press, New York. (361pp) ISBN0-19-854650-5
Schutt, Bill. 2017. Cannibalism: A Perfectly Natural History. Chapel Hill, Nc, Algonquin Books Of Chapel Hill. ISBN 9781616207434
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