In the contest between predator and prey, some prey may have unique heritable characteristics that enable them to more successfully elude predators. Similarly, some predators may have characteristics that enable them to more successfully capture prey. The natural selection of characteristics that promote the most successful predators and the most elusive prey leads to coevolution of predator and prey. In other cases, two species may evolve so that mutual benefits increase. In general, coevolution is the evolution of one species in response to new adaptations that appear in another species. Some important examples of coevolution follow:
1. Secondary compounds are toxic chemicals produced in plants that discourage would-be herbivores.
- Tannins, commonly found in oaks, and nicotine, found in tobacco, are secondary compounds that are toxic to herbivores.
2. Camouflage (or cryptic coloration) is any color, pattern, shape, or behavior that enables an animal to blend in with its surroundings. Both prey and predator benefit from camouflage.
- The fur of the snowshoe hare is white in winter (a camouflage in snow) and brown in summer (a camouflage against the exposed soil).
- The larvae of certain moths are colored so that they look like bird droppings.
- The markings on tigers and many other cats provide camouflage in a forested background. In contrast, the yellow-brown coloring of lions provides camouflage in their savanna habitat.
- Some plants escape predation because they have the shape and color of the surrounding rocks.
3. Aposematic coloration (or warning coloration) is a conspicuous pattern or coloration of animals that warns predators that they sting, bite, taste bad, or are otherwise to be avoided.
- Predators learn to associate the yellow and black body of bees with danger.
4. Mimicry occurs when two or more species resemble one another in appearance. There are two kinds of mimicry:
- Müllerian mimicry occurs when several animals, all with some special defense mechanism, share the same coloration. Müllerian mimicry is an effective strategy because a single pattern, shared among several animals, is more easily learned by a predator than would be a different pattern for every animal. Thus, bees, yellow jackets, and wasps all have yellow and black body markings.
- Batesian mimicry occurs when an animal without any special defense mechanism mimics the coloration of an animal that does possess a defense. For example, some defenseless flies have yellow and black markings but are avoided by predators because they resemble the warning coloration of bees.
5. Pollination of many kinds of flowers occurs as a result of the coevolution of finely-tuned traits between the flowers and their pollinators.
- Pollen from flowers of the Yucca plant is collected by yucca moths. Pollination is accomplished when the moths roll the pollen into a ball, carry it to another Yucca plant, and deposit it on the stigma of a flower. The moth also deposits its eggs into some of the flower’s ovules, but only about a third of the flower’s seeds are eaten by the moth larvae after hatching from the eggs. There are no other pollinators for Yucca and no other hosts for yucca moth egg-laying.
- Red, tubular flowers with no odor have coevolved with hummingbirds who are attracted to red and have long beaks and little sense of smell. The flowers provide a copious amount of nectar in exchange for the transfer of their pollen to other flowers.