1. BIOLOGY 12 Evolution - Evolution of Populations
- Disruptions to Equilibrium
- Coevolution
- Pace
- New Species

2. Evolution of Populations - Mechanisms
population – localized groups of individuals belonging to the same species
gene pool – all of the genes present in a species population
gene (allele) frequency – proportion of each gene (allele) in the gene pool
genetic equilibrium – stability of the frequency of genes in successive generations of a population

3. Evolution of Populations…
natural selection has an effect only on the phenotype of an organism
therefore heterozygote genotypes preserve recessive genes in populations and variety is conserved
*if frequencies change, equilibrium is broken and evolution occurs*

4. Disruptions to equilibrium are caused by:
1) mutations
2) genetic drift – changes in the gene pool of a population due to chance
two types:
A) bottleneck effect – genetic drift that results from a sudden decrease in population due to environmental factors (fire, flood etc.)
B) founder effect – genetic drift that results from a small population colonizing a new area

5. Bottleneck Effect

6. Example of a Bottleneck
Northern Elephant Seals
population reduced to as few as 20 individuals (due to hunting)
population has now recovered to over
but little genetic variation

7. Disruptions to equilibrium continued…
3) gene flow (migration) – the loss or gain of alleles from a population due to the migration of fertile individuals or the transfer of gametes between a population

8. Coevolution when two or more species influence each others evolution
examples:
flowering plants and their pollinators
predator prey relationships (newts)
leaf cutter ants and fungi
humans and symbiotic bacteria
humans and pathogenic bacteria (resistant TB)

9. Pace of Evolution two theories:
1) gradualism: states that populations slowly diverge from one another by the accumulation of adaptive characteristics within a population
*if this theory is correct, we would expect to find many intermediate forms of species within the fossil record; scientists have found intermediate forms of only a few species, but some argue this is due to an incomplete fossil record

10. Pace of Evolution continued…
2) punctuated equilibrium: evolution proceeds with periods of inactivity (with little or no change) followed by very active phases, so that major adaptations or clusters of adaptations appear suddenly in the fossil record
*this is supported by species who have not evolved in millions of years and others that have changed a lot within the last ~ years

11. How do new species arise?
Divergent evolution: evolution in which related species progressively differentiate
a major type of divergent evolution is Adaptive radiation: the emergence of numerous species from a common ancestor introduced to an environment presenting a diversity of new opportunities and problems

12. Textbook Questions 1 – page 518 1 – page 528 7 – page 533
10 and 16 – page 540
1,3,4 and 5 – page 555
4 – page 605