Predator/Prey Interactions

You may remember that a predator is an animal that hunts and kills other animals for food. Conversely, prey is a term used to describe animals that are hunted and killed by predators. Now, for the purposes of this lesson, when I talk about predators and prey, we can also think of herbivores as predators of plants and plants as prey of herbivores. The interactions between a predator and its prey, as well as the interactions between an herbivore and the plants it eats, are some of the most powerful driving forces behind evolution.

Predation is a strong, selective pressure that drives prey organisms to find ways to avoid being eaten. Prey organisms that are difficult to find, catch or consume are the ones that will survive and reproduce. The result is that over evolutionary time, prey organisms have developed a stunning array of strategies to avoid being eaten. Some defensive strategies are pretty obvious, and top among the list of obvious strategies is running away. Gazelle, deer, small mammals and lizards often rely on their speed and quickness to escape predators, and many birds rely on flight as their primary defensive strategy. Some organisms, like armadillos, tortoises, porcupines and thorny plants, use armor, quills and thorns to defend themselves against predators.

Camouflage

The orchid mantis is an example of a predator that uses camouflage to its advantage

Chemical Warfare

Some organisms have resorted to chemical warfare to defend themselves against predators. The very distinctive-smelling spray of the skunk comes to mind, and the bombardier beetle sprays would-be predators with a toxic chemical in a similar fashion. Some organisms are themselves poisonous, like this poison dart frog. Animals that use chemicals as a defense rarely use camouflage; quite the opposite, in fact. These animals are usually brightly and distinctively colored to stand out. These markings are called warning coloration and are bright or distinctive markings that serve as a warning to would-be predators.

Monarch and viceroy butterflies exhibit Mullerian mimicry

A very common and universally known warning coloration is the black and yellow stripes of many species of wasps, hornets and bees. Some harmless species of flies, and even some beetles, have developed similar black and yellow coloration to mimic the potentially dangerous wasps and bees. This type of mimicry, where a harmless animal mimics a dangerous or unpalatable animal, is called Batesian mimicry. Many types of butterflies also practice Batesian mimicry. However, there are cases where two or more dangerous or unpalatable species all resemble one another. This type of mimicry is called Mullerian mimicry. The monarch butterfly shown on the left and the viceroy butterfly shown on the right will make animals sick or taste very bad if they are eaten. When two unpalatable species resemble each other, they reinforce avoidance by predators by increasing the frequency of unfavorable encounters. The predators learn faster, and fewer butterflies of both species are eaten during the learning process.

Offensive Strategies of Predators

So far, we've focused mainly on defensive strategies used by prey, but predators can also use some of the strategies already mentioned to help them capture or kill their prey. Cheetahs use speed to outrun their prey, and eagles, hawks, owls and falcons use flight to their advantage while hunting. Venomous snakes, spiders and wasps use poisons to either kill or immobilize their prey. Some predators even use mimicry to capture prey. The alligator snapping turtle uses its pink worm-like tongue as a lure to draw fish right into its mouth. The turtle will sit submerged underwater with its mouth wide open and flail its tongue around like a writhing worm. When an unsuspecting fish goes after the tongue, the turtle snaps its mouth shut and eats the fish instead.