Müllerian mimicry

Müllerian mimicry is a natural phenomenon in which two or more distasteful species, that may or may not be closely related and share one or more common predators, have come to mimic each other's warning signals. It is named after the German naturalist Fritz Müller, who first proposed the concept in 1878.

The phenomenon can be understood by imagining two distasteful species that do not resemble one another and are also prey to a common predator. Occasionally, individuals of the predatory third species will encounter one or the other type of noxious prey, and thereafter avoid it. Predators that avoid only one of the harmful species provide no benefit to individuals of the other species. Therefore, it would be advantageous if the appearances of the two prey species were more similar. This is because a predator that learns to avoid either species in a pair of species exhibiting Müllerian mimicry learns, in effect, to avoid both.

Müllerian mimicry was proposed by the German zoologist and naturalist Johann Friedrich Theodor Müller (1821–1897), always known as Fritz. An early proponent of evolution, Müller offered the first explanation for resemblance between certain butterflies that had puzzled the English naturalist Henry Walter Bates, who, like Müller, spent a significant part of his life in Brazil. Müller had also seen these butterflies first hand, and collected specimens like Bates.

Understanding Müllerian mimicry is impossible without first understanding aposematism, or warning signals. Dangerous organisms with these honest signals are avoided by predators, who quickly learn after a bad experience not to pursue the same prey again. Learning is not actually necessary for animals which instinctively avoid certain prey; however, learning from experience is much more common. The underlying concept with predators that learn is that the warning signal makes the harmful organism easier to remember than if it remained as cryptic as possible (e.g. being still and silent, providing no scent, and being well camouflaged). Aposematism and crypsis are in this way opposing concepts, but this does not mean they are mutually exclusive. Many animals remain inconspicuous until threatened, then suddenly employ warning signals, such as startling eyespots, bright colors on their undersides or loud vocalizations. In this way, they enjoy the best of both strategies. These strategies may also be employed differentially throughout stages of development. For instance, large white butterflies are aposematic as larvae, but are Müllerian mimics once they emerge from the final stages of development as butterflies.

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