Feral organism

A feral animal (from Latin fera, "a wild beast") is an animal living in the wild but descended from domesticated individuals.

As with an introduced species, the introduction of feral animals or plants to non-native regions may disrupt ecosystems and has, in some cases, contributed to extinction of indigenous species.

According to dictionary definitions a feral animal is one that has itself escaped from a domestic or captive status and is living more or less as a wild animal, or one that is descended from such animals. Other definitions define a feral animal as one that has changed from being domesticated to being wild, natural, or untamed. Some common examples of animals with feral populations are horses, dogs, goats, cats, and pigs.

Zoologists generally exclude from the "feral" category animals that were genuinely wild before they escaped from captivity: neither lions escaped from a zoo nor the sea eagles (Haliaeetus albicilla) recently re-introduced into the UK are regarded as feral. Wild (i.e. non-domesticated) species naturalized into a new territory are not normally considered feral animals.

Domesticated plants that revert to wild are referred to as escaped, introduced, naturalized, or sometimes as feral crops. Individual plants are known as volunteers. Large numbers of escaped plants may become a noxious weed. The adaptive and ecological variables seen in plants that go wild closely resemble those of animals. Feral populations of crop plants, along with hybridization between crop plants and their wild relatives, brings a risk that genetically engineered characteristics such as pesticide resistance could be transferred to weed plants. The unintended presence of genetically modified crop plants or of the modified traits in other plants as a result of cross-breeding is known as "adventitious presence (AP)".

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