What Makes Animals Cannibals?

What Makes Animals Cannibals?

From amoebas swallowing each other to polar bears devouring cubs, cannibalism . is all over the natural world HTML3_ HTML3_ However, it is a risky way of getting food. Animals from the same species have similar natural defenses and can share diseases. Genetic success is often undermined by eating one’s offspring. What is it that makes some animals more successful?

” Almost all predators cannibalize when the situation is not good enough,” Jay Rosenheim, an entomologist from the University of California, Davis, says. Some desperate herbivores do, too, he adds. Rosenheim began to investigate the motivations behind canibalization after seeing big-eyed predators in California cotton fields eat their eggs.

” The density of the population is often what throws that switch,” Rosenheim states. For a study in Ecology, his team synthesized more than three decades of published research to construct a mathematical model coupling such density to cannibalism.

” It seems so absurd, but density dependence hasn’t been taken into consideration in a ton of modelling,” says Chloe Fouilloux from the University of Jyvaskyla, Finland. She was not involved in the research but studies cannibalistic and frogs. While density is a component of some models, this model focuses on density-related variables like the frequency of animals meeting one another and the likelihood that an attack will occur.

The researchers also identified specific ways that population density can cause cannibalism. Rosenheim states that cannibalism is caused by a lack of resources. Research suggests that hunger can cause certain neurohormones to spike, which encourages aggression and possibly cannibalistic behavior.

” I was thrilled to hear about their recent work on the [physiological] mechanism underlying cannibalism,” Fouilloux said.

Cannibalistic behavior can also be influenced by disease spread. A sick animal might be able to eat its own kin if it is hungry. A healthy person could eat its sick neighbor, taking advantage their weak state. Rosenheim states that “the interactions of density, disease, and cannibalism have been really, really complicated.” He also says that the research area is rich in potential discoveries.

For some animals, cannibalism can be triggered by the arrival of more of their kind, even if there is plenty of food. This is what happens to female big-eyed bugs. When it gets too crowded, they behave as if the eggs are from other females. By anchoring the model in real biological conditions such as food scarcity, disease risk and increasing chances of an encounter, Fouilloux says, the researchers showed that density is “this amazing regulating factor that helps explain and contextualize the role of cannibalism in stabilizing population dynamics.”

This article was originally published with the title “Biting Distance” in Scientific American 327, 5, 19 (November 2022)

doi: 10. 1038/scientificamerican1122-19


    Fionna M. D. Samuels was a 2022 AAAS Mass Media Fellow at Scientific American. She is currently pursuing a Ph.D. degree in chemistry at Colorado State University. Follow her on Twitter @Fairy__Hedgehog

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