11.6 Patterns in Evolution KEY CONCEPT Evolution occurs in patterns.

11.6 Patterns in Evolution Evolution through natural selection is not random. Natural selection can have direction. The effects of natural selection add up over time.

11.6 Patterns in Evolution Convergent evolution describes evolution toward similar traits in unrelated species. Shark fish and dolphins mammals both have forked tail fins to propel them through water. However the tail fins of shark are vertical while the tail fins of dolphins are horizontal. Wings as analogous structures are also examples

11.6 Patterns in Evolution Divergent evolution describes evolution toward different traits in closely related species. 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 kit fox's large ears are an adaptation to its desert environment the red fox and the kit fox had a common ancestor. As they adapted to different environments, the appearance of the two species diverged How do convergent and divergent evolution illustrate the directional nature of natural selection? ancestor red fox kit fox

11.6 Patterns in Evolution Species can shape each other over time. Two or more species can evolve together through coevolution. –evolutionary paths become connected –species evolve in response to changes in each other

11.6 Patterns in Evolution Coevolution can occur in beneficial relationships. Predators and their prey sometimes coevolve; parasites and their hosts often coevolve; plant-eating animals and the plants upon which they feed also coevolve.

11.6 Patterns in Evolution 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.

11.6 Patterns in Evolution Coevolution can occur in competitive relationships, sometimes called evolutionary.

11.6 Patterns in Evolution Species can become extinct. Extinction is the elimination of a species from Earth. Background extinctions occur continuously at a very low rate. –occur at roughly the same rate as speciation –usually affects a few species in a small area –caused by local changes in environment

11.6 Patterns in Evolution Background extinctions occur continuously at a very low rate. –occur at roughly the same rate as speciation –usually affects a few species in a small area –caused by local changes in environment

11.6 Patterns in Evolution Mass extinctions are rare but much more intense. –destroy many species at global level –thought to be caused by catastrophic events –at least five mass extinctions in last 600 million years

11.6 Patterns in Evolution Speciation often occurs in patterns. A pattern of punctuated equilibrium exists in the fossil record. –theory proposed by Eldredge and Gould in 1972 –episodes of speciation occur suddenly in geologic time –followed by long periods of little evolutionary change –revised Darwin’s idea that species arose through gradual transformations

11.6 Patterns in Evolution Many species evolve from one species during adaptive radiation. –ancestral species diversifies into many descendent species –descendent species usually adapted to wide range of environments