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Evolution of Populations

Evolution of Populations. Evolution as Genetic Change. Each time an organism reproduces, it passes copies of its genes to its offspring. We can therefore view evolutionary fitness as an organism’s success in passing genes to the next generation. .

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Evolution of Populations

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  1. Evolution of Populations

  2. Evolution as Genetic Change • Each time an organism reproduces, it passes copies of its genes to its offspring. • We can therefore view evolutionary fitness as an organism’s success in passing genes to the next generation.

  3. If an individual dies without reproducing, the individual does not contribute its alleles to the population’s gene pool. • If an individual produces many offspring, its alleles stay in the gene pool and may increase in frequency. • It is populations, not individual organisms, that can evolve over time!

  4. Types of Selection • Directional – individual at one end of the curve have higher fitness than individuals in the middle or at the other end. • Disruptive- individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle. • Stabilizing -individuals near the center of the curve have higher fitness than individuals at either end.

  5. The Process of Speciation • Define species: -group of similar organisms that can breed and produce fertile offspring

  6. So…what must happen for a species to evolve into two new species?

  7. -speciation- • The gene pools of two populations must become separated for them to become new species. • When the members of two populations cannot interbreed and produce fertile offspring, reproductive isolation has occurred. • Behavioral , Geographic, and Temporalisolation can all lead to reproductive isolation.

  8. Behavioral Isolation– courtship behaviors, songs, etc. The Western meadowlark (left) and the Eastern meadowlark (right) appear to be identical, and their ranges overlap, but their distinct songs prevent interbreeding.

  9. Geographic Isolation– Separation of populations caused by a physical barrier; rivers, rising mountain chains, vegetations differences, etc. Mountains, rivers even roads can separate two populations of the same species.

  10. Temporal Isolation– Populations develop separate mating seasons. Temporal refers to timing. Timing for mating, migrating, feeding etc. Examples: * Different species of plants frequently have different mating seasons * Closely related species of fireflies frequently mate at different times of night

  11. Wrap Up…Reproductive Isolation • When two variations of the same species can no longer interbreed because they are separated by time, behavior or location… • …they have experienced reproductive isolation. They are no longer part of the same species. They are two different species. • Speciation has occurred!

  12. Which of the following explains this phenomenon? a. Competition b. Extinction c. Predation d. Speciation

  13. Practice Question Which of the following is an adaptation most likely observed in plants growing along Aransas Bay (red dot on map)? A Sensitivity to green light B Tolerance of saltwater C Extension of root length D Resistance to predation

  14. Practice Question The myxoma virus was used to control an overpopulation of European rabbits in Australia. When first introduced in the mid-1900s, the virus greatly reduced the European rabbit population. Today the virus is not an effective control of the European rabbit population. Fewer European rabbits are affected by the virus today because they have — F learned to avoid the virus G moved away from infected areas H undergone a change in diet J developed resistance to the virus

  15. Practice Question Some mesquite trees have deeper roots than any other plant in the desert. How are deep roots an adaptation for survival in the desert? F Deep roots can protect the tree from predators. G Roots encounter cooler conditions far below the desert surface. H Roots can extend great distances to reach water. J Deep roots interact with beneficial bacteria below the surface.

  16. Practice Question F Birds become confused by the bug’scoloration, so the bug has time to escape. G Birds associate the bug’s coloration with its bad taste and avoid eating it. H Birds are unable to locate the bug’s head, so the bug can escape. J Birds cannot locate the bug because it appears to be part of the plant. Which of the following best explains how the milkweed bug’s coloration helps it avoid being eaten by birds?

  17. Practice Question The guppy is a species of small freshwater fish. Scientists observed that the average size of guppies in a pond decreased over a few years after a guppy predator was introduced into the pond. Which of the following best explains the change in guppy size? F Speciation G Convergent evolution H Inbreeding J Natural selection

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