Animal Behavior/The Monarch Butterfly
Antipredator Adaptations used by the Monarch Butterfly
The relationship between prey and predators continually changes. Most monarch butterflies do not live very long.
That's why they are endangered. One way monarch butterflies increase their fitness is by forming huge groups of up to ten million. As their group size increases, the probability that any one monarch butterfly will be captured decreases. Moreover, the butterflies located in the center of a large group are more likely to survive than those on the outside (Pike, 1999). This is known as the “dilution effect (Alcock, 2001).”
Monarch butterflies that choose to migrate to closed-area overwintering sites are less likely to be attacked by a predator. Also, by reacting as a group to the movement of a predator, monarch butterflies are better able to scare away predators (Pike, 1999). This “mass startle effect” is thought to stun the predators and provide time for the butterfly to escape (true shock and awe indeed).
The aforementioned are collective ways in which the butterfly behaves in order to elude a predator. There are, however, certain individual inherent features that the monarch butterflies possess that increase their probability of avoiding a predator.
Monarch butterflies contain chemicals that are toxic to many predators. Evidently, this makes other similar but harmless species envious. In Batesian mimicry, a palatable species attempts to mimic an unpalatable species in an attempt to increase its own fitness. The monarch butterfly species is one that some Batesian mimics model themselves after perhaps because the monarch butterflies are so successful at avoiding predators (Mappes, 1997). The Batesian mimics, although they are not harmful to predators, experience increased fitness because they model a potentially harmful species such as the monarch butterfly. The viceroy butterfly (Limenitis archippus) is one such butterfly that models itself after the monarch (Pike, 1999).
Although monarch butterflies do not gain an increase in fitness as models of Batesian mimics, they do benefit from Müllerian mimicry. In Müllerian mimicry, two unrelated, toxic species converge on a similar morphology. If more than one unpalatable species has a similar morphological trait, then the predators may more easily recognize a Müllerian mimic as potentially harmful. This saves both the mimics and the predators time and energy.
Lastly, monarch butterflies display aposematism or warning coloration. This warning coloration is meant to be very conspicuous (Alcock, 2001). Monarch butterflies make themselves conspicuous by having bright orange areas on its wings. Predators quickly learn that prey containing these bright colors are potentially harmful. For example, when a blue jay consumes a monarch butterfly, it vomits shortly after. From that point on, the blue jay associates features of the monarch butterfly, such as its bright colors, as unpalatable (Alcock, 2001). Because of their morphological features, Batesian mimics, Müllerian mimics, and many other aposematic species all gain from the monarch’s unpalatability.
Alcock, John. Animal Behavior: An Evolutionary Approach, Seventh Edition. Massachusetts: Sinauer Associates, Inc., 2001
Mappes, J., Alatalo, R.V. “Batesian mimicry and signal accuracy.” Evolution 51 (1997): 2051-2053.
Pike, Kim. “Antipredator Adaptations by Monarch Butterflies.” Entomology at Colorado State University. Posted in 1999. Colorado State University. Accessed December 6, 2004.