1. Island Evolution, Natural Selection and Darwin’s Finches
Measuring Natural selection and evolution using island environments

2. Biological Evolution on Islands
Islands are unique because they are similar
Unique effects
Similar processes
Islands are smaller versions of continents
Smaller size + populations
Fewer species/Less complexity
Change occurs more rapidly

3. Biological Evolution on Islands
Island Evolution
Predictable
Deterministic
Natural Selection
“Survival of the fittest”
Genetic Drift
“Survival of the lucky”
Random
Stochastic
Both are easier to observe/study on islands

4. Island Evolution - Unique Effects
Dispersal Ability/Loss of Dispersal Ability
Island species must be good at dispersal/ colonization
Often show loss of dispersal ability after colonization
Kiwi – New Zealand
Dodo - Mauritius

5. Island Evolution - Unique Effects
Size Change
Dwarfism
Gigantism
Pygmy Hipp0 - Madagascar
Giant Tortoise - Galapagos

6. Island Evolution - Unique Effects
Loss of defensive mechanisms
Lack of predators
Lesser Bird of Paradise – New Guinea
Rattleless Rattlesnake – Santa Catalina

7. Island Evolution - Process
Survive
Reproduce
Adapt
Evolve
Migrate
Don’t Survive
Don’t Reproduce
Don’t
Adapt
Extinction
Evolution and Extinction occur at faster rates on islands

8. Measuring Natural Selection and Evolution
Peter and Rosemary Grant – Princeton University
Research from 1973 – present
Research on Daphne Major in Galapagos Islands
Small island with simple ecology
Able to mark, measure and track every bird, every birth, every death

9. Galapagos Islands
Daphne Major

10. Daphne Major Daphne Major from the air Area = 0.31 km2
Elevation = 120 m
Peter and Rosemary Grant in 2010
Spent 30+ research seasons on Daphne Major

11. Daphne Major
Plants/Finch Food
Prickly Pear Cacti
Tribulus seeds

12. Darwin’s Finches Geospiza scandens Geospiza magnirostris
Geospiza fortis

13. Beak shapes and sizes are adapted to bird’s primary food source
Darwin’s Finches
Beak shapes and sizes are adapted to bird’s primary food source

14. °=1976 population and • =1978 population
Research
Question 1: Is beak size inherited/heritable?
What hypothesis?
What data to collect?
Offspring Bill Depth (mm)
Midparent Bill Depth (mm)
°=1976 population and • =1978 population

15. Research Question 2: Did natural selection occur? What hypothesis?
What data to collect?

16. Natural Selection Data
Natural Selection = differential survival

17. Research Question 3: Did evolution occur? What hypothesis?
What data to collect?

18. Evolution = Change over time
Evolution Data
Evolution = Change over time

19. Conclusions Natural selection occurred in extended dry season of 1977
Birds lived and died based on beak size, where large beak size was advantageous in cracking large seeds
Evolution occurred between 1976 and 1978
Beak size of population increased because of survivor reproduction

20. Conclusions
Natural selection occurred in the El Nino wet season of 1982
Birds lived and died based on beak size, where smaller size was advantageous in eating smaller seeds
Evolution occurred between 1981 and 1983
Beak size of population decreased because of survivor reproduction