Saturday 20 October 2007

Non-human cannibalism

Three Mormon crickets eating a fourth Mormon cricket
Cannibalism is a common ecological interaction in the animal kingdom and has been recorded for more than 1500 species (this estimate is from 1981). In sexual cannibalism as recorded for example for the female red-back spider, black widow spider, praying mantis, and scorpion the female eats the male after, during or instead of mating (though the frequency of this is often overstated).

The more common form of cannibalism is size structured cannibalism, in which large individuals consume smaller ones. In such size-structured populations, cannibalism can be responsible for 8% (Belding's Ground Squirrel) to 95% (dragonfly larvae) of the total mortality, making it a significant and important factor for population and community dynamics. Such size structured cannibalism has commonly been observed in the wild for a variety of taxa, including octopus, bats, toads, fish, monitor lizards, red-backed salamanders and several stream salamanders, crocodiles, spiders, crustaceans, birds (crows, barred owls), mammals, and a vast number of insects, such as dragonflies, diving beetles, back swimmers, water striders, flour beetles, caddisflies and many more. Unlike previously believed, cannibalism is not just a result of extreme food shortage or artificial conditions, but commonly occurs under natural conditions in a variety of species. In fact, scientists have acknowledged that it is ubiquitous in natural communities. Cannibalism seems to be especially prevalent in aquatic communities, in which up to ~90% of the organisms engage in cannibalism at some point of the life cycle. Cannibalism is also not restricted to carnivorous species, but is commonly found in herbivores and detritivores. Another common form of cannibalism is infanticide. Classical examples include the chimpanzees where groups of adult males have been observed to attack and consume their infants, and lions, where adult males commonly kill infants when they take over a new harem after replacing the previous dominant males. Also, gerbils, pigs raised for meat, hamsters and also some breeds of cats eat their young if they are stillborn, or if the mothers are especially stressed.

In the agricultural industry, savaging is the aggressive or cannibalistic behavior of mother livestock towards newborn young. This is especially prevalent in pigs.

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