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Avoiding Predation

Most animals get their food from preying on other organisms, and much of the life of animals involves eating and avoiding being eaten.

So it is not surprising to find many examples of adaptations that We shall examine some of the devices that help their owners avoid being eaten.

Camouflage (cryptic coloration)

Many animals are patterned to blend in with their surroundings.

Link to some examples.

Masquerade

Masquerading animals resemble some inanimate object and thereby escape detection by potential predators (or prey).

The motionless twig caterpillar shown here (courtesy of Muriel V. Williams) complete with "buds" and "lenticels" escapes detection by birds (but pays for its cleverness by occasionally having some other insect lay eggs on it by mistake).

Link to another example of masquerade.


Chemical Defenses

Many plants and animals use repellent chemicals to deter predation. But what if you have a powerful defensive weapon but no potential predator notices until it has launched an attack? One solution to this dilemma is the evolution of warning coloration (also called aposematic coloration).

Aposematic Coloration

This is the larva of the monarch butterfly; an example of aposematic coloration. There is no question of camouflage here. Rather this creature is advertising its presence.

The milkweed leaves on which it is feeding contain cardiac glycosides that are toxic to vertebrates because they block the activity of the Na+/K+ ATPase that is essential for many cell functions [Link]. The larva stores these within its body and thus becomes unpalatable to vertebrate predators.

The chemicals remain in the body even after metamorphosis, so that adults are unpalatable as well.

In these photographs (provided by Lincoln P. Brower) a blue jay eats a portion of a monarch butterfly (left) that had fed (in its larval stage) on poisonous milkweed. A short time later, the blue jay vomits (right). Following this episode, the blue jay refused to eat any other monarch offered to it.



Mimicry

Batesian Mimicry

If an animal is not noxious to potential predators, why not look like an animal that is?

Some examples:

This phenomenon is called Batesian mimicry (named after Henry W. Bates, a nineteenth-century naturalist who studied many such cases).

Müllerian Mimicry

Some unpalatable animals closely resemble other equally unpalatable species. Such mimicry is called Müllerian mimicry (in honor of the German zoologist Fritz Müller, who studied it). Presumably each species gains a measure of protection from the occasional, but educational, losses of the other species to predators.

Lincoln Brower, who has studied the monarch and viceroy, believes that the viceroy is as unpalatable to potential predators as the monarch, and thus is really an example of Müllerian mimicry.

Aggressive Mimicry

Some carnivores have evolved devices with which they mimic the prey (or potential mate) of other (usually smaller) predators. They use these devices as lures.

Two examples:

Group Behavior

Cooperation between members of a social species often reduces the severity of predation.
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22 September 2012