Natural Selection & Adaptation

1. Natural Selection & Adaptation Unit 9 7C

2. Natural Selection • Gradual process by which biological traits become either more or less common in a population

4. Nature basically “selects” certain individuals to be successful and reproduce and over time the population changes due to this selection.

5. What has happened to the mice population below? The population has changed from 50% brown & 50% white to 80% white & 20% brown. WHY?

6. Adaptations Cause Fitness • Adaptation– any inherited characteristic that increases an organism’s chance of survival. (Remember the source of any new trait is a mutation.) • Adaptations make an organism better suited to the environment. So in the struggle for survival, organisms with adaptations suited to the environment will be more likely to survive and reproduce.

7. Fit offspring then survive and reproduce and even more offspring are “born” that have the adaptation. • Over generations, the DNA in the whole population changes, so that all the population has the adaptation that makes the population fit for its environment.

8. Fitness • The ability of an organism to survive and reproduce

9. Which lion is more fit? If fitness is the ability to survive & reproduce

10. This lion will hunt for more food, have the energy to reproduce, and pass on his genes to his offspring.

11. Traits that help an organism survive • Survive a predator • Survive disease • Compete for food • Compete for territory

12. Traits that help individuals reproduce • Attracting a mate • Compete for nesting sites • Successfully raising young

13. “Survival of the Fittest” • Faster, stronger, good hunter, better camouflaged • Best organism that survives and reproduces

14. Mesquite have the longest tap root of any desert species

15. Adaptation • Any characteristic that increases fitness

18. Types of Selection

19. Types of Selection Disruptive Selection • Describes changes in population genetics in which extreme values for a trait are favored over medium values. • The variance of the trait increases and the population is divided into 2 distinct groups.

22. Types of Selection Stabilizing Selection • Genetic decreases as the population stabilizes on a particular trait or value. It varies medium traits. “Average Joe wins” • Opposite of disruptive selection.

25. Types of Selection Directional Selection • A single phenotype is favored, causing the allele frequency to continuously shift in 1 direction. • Occurs under environmental changes when populations migrate to new areas with different environmental pressures.

28. Natural Selection Summary Points • Inherited variation – there are genetic variations (differences) between individuals of a population • The more genetic diversity, the more variations of alleles that are suited for the environment. The more offspring will survive and reproduce. • The population will then continue.

29. Natural Selection Summary Points • Overproduction of offspring – there are more offspring are produced than can survive • Struggle for existence – there is competition for survival among the members of the population

30. Witness to Evolution • Peppered Moth • 2 types: dark vs. light Peppered moth

31. Peppered moth • Why did the population change? • early 1800s = pre-industrial England • low pollution • lichen on trees = light colored bark • late 1800s = industrial • factories = soot coated trees • killed lichen = dark colored bark • mid 1900s = pollution controls • clean air laws • return of lichen = light colored bark

32. Peppered moth: Evolution in action Year% dark% light 1848595 1895982 19951981 clean air, light-colored bark pollution, dark-colored bark Clean Air Act, light-colored bark industrial melanism

33. Natural Selection & Fitness Unit 9 7D

34. Genetic or Inherited Variation • variation in alleles of genes that occurs both within and among populations

37. What determines these different traits or variations? • Mutations in our DNA • crossing over & independent assortment in meiosis.

38. Let’s remember… • Genotype is the individuals set of alleles for a trait… BB, Bb, or bb • Phenotype is the appearance or expression of the trait… Homozygous black, heterozygous black, or homozygous brown

40. 64% of the total mouse population has black fur • The black allele (B) occurs 40% of the time while the brown allele (b) occurs 60% of the time. • The brown allele occurs more frequently than the black. What change in the habitat could change the frequency of alleles?

41. Elements of Natural Selection • Inherited Variation • Producing More offspring than can survive • Limited (finite) supply of Environmental Resources

42. Inherited Variation • In an environment that favors black fur, mice with brown fur will be eaten, and the frequency of the allele for brown fur (b) will decrease. Black mice will have a better chance of surviving and passing on their alleles to their offspring.

43. The frequency for the while allele in the mouse population below will decrease.

44. Producing More offspring than can survive • Most populations produce more offspring than can survive. Many offspring are lost due to predation, starvation, etc… The offspring that do survive to adulthood will have phenotypes that give them an advantage within that environment over those that didn’t survive & reproduce.

45. Limited (finite) Supply of Resources • Individuals compete for food, water, space, & shelter. • When resources become scarce, such as during a drought, competition increases. Populations decline, and the individual with advantageous traits will survive and reproduce.

47. The ground finches with larger beaks can eat a wider variety of seeds & nuts. If a drought occurs, the finches with smaller beaks will run out of food & the population of finches with larger beaks will increase.

48. Natural Selection & Diversity Unit 9 7E

49. Speciation • the evolutionary process by which new biological species arise

50. Remember… • Every species has different DNA. • Species can breed and produce fertile offspring.