Patterns in Evolution
Key concept : Evolution occurs in patterns Evolution through natural selection is not random. Natural selection can have direction. The effects of natural selection add up over time.
Convergent Evolution Defined: evolution toward similar traits in unrelated species due to a similar environment. Ex: Tuna (fish) and dolphins (mammals). They are an unrelated species living in a similar environment, the ocean. Faced similar evolutionary pressures.
Kaibab Squirrel (Grand Canyon) Divergent Evolution Kaibab Squirrel (Grand Canyon) ancestor red fox kit fox Defined: Describes evolution toward different traits in closely related species. Cause: Different environments
Coevolution Defined: Two or more species evolve in response to changes in each other Evolutionary paths become connected Both species receive benefits from the other as a result of adaptations. Ex: Plants and Insects Plants: provide insects with nectar Insect: transfers pollen from one plant to another
Coevolution Continued… Coevolution can occur in competitive relationships, sometimes called an evolutionary arms race. Example: Crab vs. Snail & Bacteria vs. Humans
Most bacteria killed Strong Survive Bacterial Resistance Strong Reproduce
Extinction Defined: The elimination of a species from Earth. Mass Extinctions: Cause: Catastrophic events Ice Age, Meteorites Destroys many species at global level Very severe Rare but much more intense At least 5 mass extinctions in last 600 million years Background Extinctions: Cause: Local changes in environment Forest fires, habitat destruction. Affects a few species in a small area Less severe. Occur at roughly the same rate as speciation
How Fast Does Evolution Occur? No exact time frame Punctuated Equilibrium: Long periods of little change are interrupted by shorter periods of rapid change. Due to sudden environment change Ex: Mammal diversity exploded after dinosaur extinction Gradualism: Slow & steady change of 1 species into another Small changes continually build over time
Gradualism of the Horse
How Fast Does Evolution Occur? To radiate = to s-p-r-e-a-d out Adaptive radiation: A process of evolution where one species can split into a number of different species. Ancestral species diversifies into many descendent species Each adapted to a different environment Ex: Mammals
Review How is convergent and divergent evolution different? What is thought to bring different organisms such as fish and dolphins to have evolved a similar body plan? What is coevolution? What does a flower gain from a close relationship with a hummingbird? What does the hummingbird gain? How is gradualism and punctuated equilibrium different?