1. Evolution and Populations How Populations Change

2. What do we know?
We know that ecosystems are made of biotic and abiotic factors.
Identify two biotic factors and two abiotic factors found in this ecosystem.

3. What do we know?
Pines will change to…
We know that ecosystems change through the process of ecological succession.
Hardwoods

4. What do we know?
We know that organisms have adaptations that increase their chances of surviving and reproducing.
Eggs
What adaptations does the blue crab have that helps it survive?

5. What do we know? We know that organisms compete over resources.
We know competition results in one species surviving and the other species dying or living a different way.
Lions and hyenas fill similar niches – why do both survive?

6. What we DON’T know? But where do the adaptations come from?
How do populations of organisms get these adaptations?

7. Evolution
Many scientists believe that the organisms we see today came from organisms that lived long ago.
They believe in a process of evolution through natural selection.
Fossilized Extinct Sloth-see the long toes!
The modern sloth – slightly different, but very similar.

8. Evolution
Evolution is the idea that organisms change over a period of time.
Evidence does exist to support this theory but it is a difficult theory to test.

9. Charles Darwin
Charles Darwin was a naturalist scientist aboard the H.M.S. Beagle in 1831.
His job was to collect organisms and catalog them for scientific study.

10. Charles Darwin He began to notice several things:
Animals were well adapted to their habitats.
Similar niches on different continents were filled by different animals.
Although the animals were different, they had similar traits.
Some living animals were similar to fossils of extinct animals.

11. Charles Darwin Darwin was influenced by many scientists of the time.
Charles Lyell proposed that geology provided evidence of a VERY old earth.
Others proposed ideas of inheriting traits. (Lamark – Acquired characteristics: a VERY wrong idea)

12. Charles Darwin
Darwin combined his observations with the ideas of other scientists and developed a hypothesis.
This hypothesis proposes that, over time, natural selection produces organisms that are able to survive in changing environments.
This is sometimes called “Survival of the Fittest”.

13. Two Different Approaches to Natural Selection
Gradualism – the idea that organisms change a little each generation, eventually developing into another species.
Punctuated Equilibrium – the idea that organisms remain stable for long periods of time and then quickly (geological time wise) change into new species.

14. Natural Selection: Survival of the Fittest
Natural selection is based on the fact that genetic variation exists in all populations – some variations are good and some aren’t.

15. Genetic Variation
Ecologists refer to the variety of genes in a population as genetic diversity or genetic variation.
Genetic variation (diversity) results from mutations and gene shuffling during sexual reproduction.

16. Natural Selection: Survival of the Fittest
Organisms with good variations are selected “for” and survive; passing the genes to their offspring.
Organisms with bad variations are selected “against” and die. No offspring.

17. Genetic Variation
This genetic variation results in physical variations (phenotypes) within a population.
This variation ensures that some of the population will survive if the habitat of the organisms changes.

18. Types of Selection
Natural selection can change the frequency of phenotypes in a population in three ways:
Directional Selection
Stabilizing Selection
Disruptive Selection

19. Directional Selection
This occurs when organisms at one end of the phenotype curve have a higher “fitness” – their genes are better so they live!
They reproduce better and the new members with the “fit” genes replace the unfit members.

20. Stabilizing Selection
This occurs when the organisms in the middle of the curve have the highest “fitness”.
The curve doesn’t move at all – so the population doesn’t change.

21. Disruptive Selection
This occurs when organisms at both ends of the curve have high “fitness” so they survive and the middle of the curve dies out.
This eventually creates two different populations.
After a period of time, they may develop into two different species.

22. Genetic Drift
Organisms can also evolve through a process called GENETIC DRIFT.
Sometimes a small group of organisms will move away from the main population and begin a new population somewhere else.

23. Genetic Drift
This small group may not have the same genetic variation as the original population.
This is called the Founder’s Effect.
Original Population

24. Speciation: How to make new species!
Genetic variation allows for the production of a new species when gene pools become isolated (separated) from each other.
This separation is known as Divergent Evolution and when populations become reproductively isolated.

25. Reproductive Isolation
One type of reproductive isolation is BEHAVIORAL ISOLATION.
Organisms don’t recognize courtship behaviors and don’t reproduce.

26. Reproductive Isolation
A second way to have reproductive isolation is through GEOGRAPHIC ISOLATION.
Here the organisms are separated by a physical barrier such as a mountain range, river, or island in the ocean.

27. Reproductive Isolation
A third method of reproductive isolation is through Temporal Isolation.
Even though similar organisms live in the same area, their breeding times are different so they never interbreed.

28. Back to Darwin’s Finches
So, how did the Galapagos Finches develop into different species?
1st: The Founder’s Effect (small group showed up.)
2nd: Geographic Isolation didn’t allow the groups to breed.
3rd: Natural Selection selected the birds with the best “fitness” so they reproduced and passed their genes to their offspring.

29. The Result: Adaptive Radiation
At least 7 different species of finch that all originally came from the same ancestor.
The development of several new species from one species is known as Adaptive Radiation.