2Key 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.
3Convergent EvolutionDefined: 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.
4Kaibab Squirrel (Grand Canyon) Divergent EvolutionKaibab Squirrel (Grand Canyon)ancestorred foxkit foxDefined: Describes evolution toward different traits in closely related species.Cause: Different environments
5CoevolutionDefined: Two or more species evolve in response to changes in each otherEvolutionary paths become connectedBoth species receive benefits from the other as a result of adaptations.Ex: Plants and InsectsPlants: provide insects with nectarInsect: transfers pollen from one plant to another
6Coevolution Continued… Coevolution can occur in competitive relationships, sometimes called an evolutionary arms race.Example: Crab vs. Snail & Bacteria vs. Humans
8Extinction Defined: The elimination of a species from Earth. Mass Extinctions:Cause: Catastrophic eventsIce Age, MeteoritesDestroys many species at global levelVery severeRare but much more intenseAt least 5 mass extinctions in last 600 million yearsBackground Extinctions:Cause: Local changes in environmentForest fires, habitat destruction.Affects a few species in a small areaLess severe.Occur at roughly the same rate as speciation
9How Fast Does Evolution Occur? No exact time framePunctuated Equilibrium: Long periods of little change are interrupted by shorter periods of rapid change.Due to sudden environment changeEx: Mammal diversity exploded after dinosaur extinctionGradualism:Slow & steady change of 1 species into anotherSmall changes continually build over time
11How Fast Does Evolution Occur? To radiate = to s-p-r-e-a-d outAdaptive radiation: A process of evolution where one species can split into a number of different species.Ancestral species diversifies into many descendent speciesEach adapted to a different environmentEx: Mammals
12Review 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?