Patterns in Evolution

Divergent Evolution Defined: closely related species become increasingly different Cause: Different environments Ex: Red fox (forest) vs. Kit fox (desert)

Kaibab Squirrel (Grand Canyon)

Convergent Evolution Defined: different species evolve similar traits due to similar habitats Survival advantage to a particular environment Ex: Tuna (fish) and dolphins (mammals) Unrelated species with a similar environment (ocean) Faced similar evolutionary pressures

Dragonfly Convergent Evolution

Coevolution Defined: 2 or more species evolve in response to changes in each other Ex: Plants and Insects Plants: provide insects with nectar Insect: transfers pollen from one plant to another

Hummingbirds: Beak shape depends on flower shape

Extinction Background Extinctions: Mass Extinctions: Less severe; local level Forest fires, habitat destruction Mass Extinctions: Very severe; global level 5 identified in earth’s history (volcanic activity, meteor strikes)

How Fast Does Evolution Occur? No exact time frame Gradualism: slow & steady change of 1 species into another Small changes continually build Punctuated Equilibrium: Rapid periods of evolution Due to sudden environment change Ex: Mammal diversity exploded after dinosaur extinction Examples of both models exist

Gradualism of the Horse