Batesian mimicry

Batesian mimicry is a form of mimicry wherein a harmless species has evolved to imitate the warning signals of a harmful species in order to benefit from these signals' tendency to deter their mutual predators. It is named after the English naturalist Henry Walter Bates, who worked on butterflies in the rainforests of Brazil.

Batesian mimicry is the most commonly-known and widely-studied of the mimicry complexes, such that the word "mimicry" is often synonymous with the type described by Batesian mimicry. However, there are many other forms of mimicry, some very similar in principle to the Batesian variety, others far separated.

Batesian mimicry is often compared with Müllerian mimicry, the mutually beneficial, converging appearance of two or more harmful species. Batesian mimicry is often thought to be diametrically opposed to aggressive mimicry, wherein a predator or parasite mimics a harmless species, thereby avoiding detection and improving its odds of a successful hunt.

In scientific studies of biological mimicry the imitating species is called the mimic, while the imitated species (protected by its own toxicity, foul taste or other defenses) is known as the model. The predatory species that mediates the indirect interaction between the mimic and the model (the interaction over evolutionary timescales by which the mimic approaches the model in appearance) is variously known as the [signal] receiver, the dupe or the operator.

By parasitising the honest warning signal of the model, the Batesian mimic gains an advantage without expending the energy required to actually arm itself. The model, on the other hand, is disadvantaged, along with the dupe. If impostors appear in large numbers then positive experiences with, and successful predation upon, the mimic may result in the model being treated as harmless. When the mimics continue to outnumber the model there is also a stronger selective advantage for the predator to distinguish mimic from model. For these reasons, in a given environment, mimics are generally less numerous than models. This is an instance of frequency-dependent selection. Some mimetic populations have evolved multiple forms (polymorphism), enabling them to mimic several different models and thereby to gain greater protection. Batesian mimicry is not always perfect. A variety of explanations have been proposed for this, including limitations in predators' cognition.

While visual signals have attracted the most study, Batesian mimicry can employ deception of any of the senses. For example, auditory Batesian mimicry can be seen in moths that mimic the ultrasonic warning signals transmitted by unpalatable moths to bat predators, while some weakly electric fish appear to mimic the electrolocation signals of strongly electric fish, constituting electrical mimicry.