Patterns of Evolution
Natural selection can ultimately lead to the formation of new species. Sometimes many species evolve from a single ancestral species. Similarities in skeletal and muscular structure of Hawaiian honeycreepers led scientists to conclude that the 23 species of honeycreepers evolved from one ancestral species. Such an evolutionary pattern, in which many related species evolved from a single ancestral species, is called adaptive radiation. Adaptive radiation most commonly occurs when a species of organisms successfully invades an isolated region where few competing species exist. If new habitats are available, new species will evolve.
Divergent and Convergent Evolution
Adaptive radiation is one example of divergent evolution. Divergent evolution is the process of two or more related species becoming more and more dissimilar. The red fox and the kit fox provide and example of two species that have undergone divergent evolution. The red fox lives in mixed farmlands and forests, where its red color helps it blend in with surrounding trees. The kit fox lives on the plains and in the deserts, where its sandy color helps conceal it from prey and predators. The ears of the kit fox are larger than those of the red fox. The kit fox's large ears are an adaptation to its desert environment. The enlarged surface area of its ears helps the fox get rid of excess body heat. Similarities in structure indicate that the red fox and the kit fox had a common ancestor. As they adapted to different environments, the appearance of the two species diverged.
In convergent evolution, on the other hand, unrelated species become more and more similar in appearance as they adapt to the same kind of environment. The two unrelated types of plants in the picture above have adapted to desert environments. Notice the resemblance of the cactus, which grows in the American desert, to the euphorbia, which grows in the African deserts. Both have fleshy stems armed with spines. These adaptations help the plants store water and ward off predators.
Coevolution is the joint change of two or more species in close interaction. Predators and their prey sometimes coevolve; parasites and their hosts often coevolve; plant-eating animals and the plants upon which they feed also coevolve. One example of coevolution is between plants and the animals that pollinate them.
In tropical regions bats visiting flowers to eat nectar. The fur on the bat's face and neck picks up pollen, which the bat transfers to the next flower it visits. Bats that feed at flowers have a slender muzzle and a long tongue with a brushed tip. These adaptations aid the bat in feeding. Flowers that have coevolved with bats are light in color. Therefore, bats, which are active at night, can easily locate them. The flowers also have a fruity odor attractive to bats.
Divergent and convergent evolution and coevolution are different ways organisms adapt to the environment. These are examples of how the diversity of life on earth is due to the ever-changing interaction between a species and its environment.