1. Evolution of Populations

2. Population vs. Species
Population-a group of organisms of the same species that live in the same area
Species-organisms that are capable of breeding AND producing fertile offspring
Ex: Lion+ Tiger= Liger Liger=infertile
Therefore lion and tiger are different species

3. Gene Pool Consists of all the genes that are present in a population
Relative frequency of an allele=the number of times an allele appears in a gene pool compared to other alleles of the same gene
Genetic Equilibrium-a population in which the frequency of alleles remains the same over generations

4. Key concepts An individual itself CANNOT evolve
Only populations can evolve
Evolution is a change in the gene pool of populations over time
If the allele frequency does not change, the population will not evolve
5 conditions are required to maintain genetic equilibrium
Random mating
Population must be very large
No movement into or out of the population
No mutations
No natural selection

5. Change in allele frequency Evolution occurred!

6. Causes of Evolution Genetic Drift
Change in the gene pool of a population that occurs by random chance
Random chance=natural disasters, disease, etc
Has a greater effect on small populations
Often causes reduction in alleles present in the gene pool
Bottleneck Effect
Founder Effect

7. Causes of Evolution-Genetic Drift
Bottleneck Effect
Results from an event/disaster that drastically reduces population size

8. Causes of Evolution-Genetic Drift
Founder Effect (Migration)
A situation in which allele frequencies change as a result of the migration of a small subgroup of a population

9. Causes of Evolution Mutations Change in an organism’s DNA
Only source of brand new genes within a population
The majority of mutations are deadly, thus are eliminated from a population

10. Causes of Evolution Gene Flow (Migration)
Genes migrate in and out of the gene pool

11. Causes of Evolution Non-random mating (sexual selection)
Inbreeding-mating between closely related partners
Selective mating-organisms prefer some individual mates over others, typically those who are similar to themselves

12. Causes of Evolution Natural Selection
Individuals better suited to their environment live to produce offspring who inherit their genes
Favored genes become more frequent in a population over time

13. 3 General Types of Natural Selection
1. Stabilizing Selection -nature selects the average form of a trait 2. Directional Selection -nature selects one extreme form of a trait 3. Disruptive Selection -nature selects both the extreme forms of a trait

14. Human babies born at an average mass are more likely to survive than babies born either much smaller or much larger than average

15. Individuals at one end of the curve have higher fitness than individuals in the middle or at the other end. A population of seed-eating birds have a food shortage that causes the supply of small seeds to run low. The beak size would change over time to beaker beaks since there are more big seeds now than little.

16. When individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle. Average sized seed becomes less common while the larger and smaller seeds become more common. The bird population then splits into two subgroups specializing in eating different sized seeds

18. How do new species form?
Speciation occurs when the gene pools of two populations become separated
As new species evolve, populations become reproductively isolated from each other
Isolation Mechanisms
Reproductive
Geographic
Temporal
Behavioral
Ecological

19. Reproductive Isolation
When members of two populations cannot interbreed and produce fertile offspring

20. Geographic Isolation Physical separation of members of a population
By formation of a canyon, mountain, river, etc
Leads to different adaptations on each side of the barrier and eventually a new species

21. Temporal Isolation
Species are isolated because they reproduce in different seasons or times of the day

22. Behavioral Isolation Species differ in their mating rituals
Different bird songs, mating colors, dances, pheromones, etc

23. Ecological Isolation
Species inhabit the same area, but different habitats, so they don’t encounter each other

24. How quickly do new species form?
2 Hypothesis
Gradualism
Many transitional forms between common ancestors and modern organisms
Punctuated Equilibrium
Sudden shifts in form from an ancestor to newer organism, so not many transitional forms between common ancestor and modern organisms

25. Patterns of Evolution Convergent Evolution Divergent Evolution
Adaptive Radiation
Artificial Selection
Coevolution

26. Convergent Evolution
Organisms appear similar, but aren’t closely related
Why?
Similar environment selects for similar traits

27. Divergent Evolution
Related populations or species become less and less alike
Adaptive radiation-type of divergent evolution that results in several variations of the species
Adaptive
Radiation

28. Divergent Evolution Artificial Selection
Humans, rather than nature, select traits

29. Coevolution
Two or more species in close association with one another change together
Predator/prey
Mollusks, like snails, have evolved thick shells and spines to avoid being eating by animals such as crabs and fish. These predators have then evolved powerful claws and jaws that compensate for the snails’ thick shells and spines
Parasite/host
Milkweed plant has leaves that contain a chemical very poisonous to most herbivores. Herbivores don’t want to eat milkweed. However, monarch butterflies have evolved the ability to tolerate these toxins. Because of this, predators don’t want to eat the monarchs since their bodies contain the poison that they eat from the milkweed
Plant/pollinator
Many plants often have long tubes that lead to their nectar. Over time, pollinators (bats, insects, etc) have evolved a long tube-like mouth that is long enough to reach in and get the nectar, while pollinating the plant at the same time.