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Outcomes of Evolution Outcomes of Natural Selection • Most quantitative traits resemble bell curve for phenotypes Natural Selection can alter variation in a population in 3 ways: 1) Stabilizing Selection • Favors individuals with the average phenotype of the trait (average form have the highest fitness) Example of Stabilizing Selection 2) Directional Selection • Environmental conditions favor individuals of one extreme phenotype Example of Directional Selection 3) Disruptive Selection • Environmental conditions favor individuals of both extremes of the phenotype. • Can lead to creation of a new species Example of Disruptive Selection Patterns of Evolution Ways species change to adapt to their habitats: o Coevolution o Convergent Evolution o Divergent Evolution Patterns of Evolution Coevolution: Two or more species change together! Examples: 1) Predator/Prey 2) Plant and pollinator Patterns of Evolution Convergent: Two dissimilar species becoming structurally similar Environment selects for similar phenotype (but ancestors were different) Patterns of Evolution Divergent: Two similar species become dissimilar in response to environment Creating a New Species Evolution Speciation and Reproductive Isolation Species: • A group of similar organisms that can breed to produce fertile offspring Liger - not fertile Speciation: • Creating a new species • 1 species evolves into 2 different species How Speciation Occurs • When a group in a population are separated and can no longer reproduce a new species is formed Ways to create a new species: how are species separated? Isolation Geographical Isolation Populations separated by geographical barriers like water, canyons, and mountains Reproductive Isolation Temporal Isolation Populations separated by time like nocturnal, diurnal, months, years Behavioral Isolation Populations separated by behaviors like mating calls, physical traits, mating dances Geographic Isolation • Habitat becomes divided • No mating because one species gets separated by a barrier (earthquake, river, etc) • Over time, can lead to two different species. Behavioral Isolation • No mating • One does not desire the courtship behavior of the other one • Over time, can lead to two different species Temporal Isolation • No mating • One reproduces at different times of day, month, year • Over time, can lead to two different species. Rates of Speciation Gradual - stable rate of change Punctuated- instant change Critical Questions: • How does reproductive isolation affect speciation? • How does geographic isolation affect speciation?