Batesian mimicry is a deceptive adaptation named after the 19th-century English naturalist Henry Walter Bates. This strategy allows a harmless organism to gain protection by copying the conspicuous warning signals of a dangerous or unpalatable species. The successful mimic uses the reputation of a toxic organism to deter shared threats, making it a powerful adaptation for prey survival.
The Three Roles in Batesian Mimicry
Batesian mimicry involves three distinct biological roles. The Model is the genuinely noxious, venomous, or unpalatable species that possesses an honest warning signal, often brightly colored, known as aposematism. This model has a defense that makes a predator regret an attack, thereby establishing the warning signal’s credibility.
The Mimic is the palatable and defenseless species that evolves to imitate the model’s warning signal without possessing any actual defense. This species gains a survival advantage by essentially bluffing its way out of an attack. The success of the mimic is entirely parasitic, relying on the model’s defense to keep the shared signal effective against predators.
The Dupe, or predator, mediates the interaction between the other two species. The dupe learns through negative experience to associate the model’s distinct warning signal with an unpleasant outcome, such as a sting or a foul taste. When the predator encounters the mimic, it avoids the harmless prey based on its learned aversion to the model’s appearance, completing the deceptive cycle.
Ecological Requirements for Success
Batesian mimicry depends on specific ecological conditions to remain sustainable. The primary condition is negative frequency dependence, which dictates that the mimic population must be significantly less numerous than the model population. If the mimics become too common, predators will frequently encounter the palatable look-alikes, causing them to question and eventually unlearn the association between the warning signal and the actual danger.
If the model is rare, the predator is less likely to have a negative encounter to reinforce its avoidance behavior, increasing the risk for both populations. The selective advantage for the mimic declines rapidly once its numbers exceed the model’s, leading to a collapse of the protective system. For the deception to work, the model and mimic must also exhibit geographic overlap, a condition known as sympatry. The mimic’s imitation must maintain sufficient signal fidelity, meaning the copy must be close enough to the model’s pattern to consistently fool the dupe.
Classic Examples in Nature
One of the most widely cited examples of Batesian mimicry involves the venomous Eastern Coral Snake and the non-venomous Scarlet Kingsnake in North America. The coral snake acts as the model, displaying bright, alternating bands of red, yellow, and black that signify its potent neurotoxic venom. The scarlet kingsnake is the mimic, possessing a nearly identical banded pattern to deter potential predators.
A simple memory aid often used to distinguish the two is based on the sequence of the colored bands: in the dangerous coral snake, the red bands touch the yellow bands, whereas in the harmless kingsnake, the red bands touch the black bands. This mimicry is effective only where the coral snake is present; studies using plasticine snake replicas found that predators attacked the harmless mimics more frequently in areas where the venomous model was absent.
Another classic, though now scientifically revised, example involves the Monarch and Viceroy butterflies. The Monarch butterfly was long considered the unpalatable model, acquiring toxins called cardenolides from its milkweed host plant, which causes birds to vomit after ingestion. The Viceroy butterfly, with its similar orange and black wing patterns, was thought to be the harmless mimic benefiting from the Monarch’s defense.
However, modern research has shown that the Viceroy is also chemically defended and unpalatable to predators, making this relationship a case of Müllerian mimicry. Despite this reclassification, the Monarch and Viceroy pairing remains a foundational case study used to introduce the concept of biological mimicry in many contexts. The Viceroy can be visually distinguished by a thin, black line that crosses the veins on its hind wings, a feature absent on the Monarch.
Distinguishing Batesian from Other Forms of Mimicry
To fully appreciate the deceptive nature of Batesian mimicry, it must be contrasted with the related phenomenon of Müllerian mimicry. The fundamental difference lies in the palatability of the mimic species. Batesian mimicry is a form of dishonesty where a defenseless organism copies the warning signal of a defended model for unilateral benefit.
Müllerian mimicry, in contrast, involves two or more species that are all genuinely unpalatable or harmful, and they share the same warning coloration. This system provides a mutual benefit because every encounter a predator has with any species in the group reinforces the avoidance signal for all others. Where Batesian mimicry is a survival bluff, Müllerian mimicry is an honest form of shared signaling that accelerates predator learning and reduces predation on every member of the mimicry ring.