1. Unit D – Population and Community Dynamics
Redding| Biology 30| 2016

2. Chapter 19: Genetic diversity in Populations
What is a Population?
Genotypic vs Phenotypic Frequencies
Hardy Weinberg Principle:

3. Hardy Weinberg

4. Hardy Weinberg 5 conditions must be met
1. The population is large enough that chance events will not alter allele frequencies.
2. Mates are chosen on a random basis.
3. There are no net mutations.
4. There is no migration.
5. There is no natural selection against any of the phenotypes.

5. Example:
A Punnett square can be used to determine the expected genotype frequencies in the next generation. In generic terms, p2 represents the homozygous dominant offspring, 2pq represents the heterozygous offspring, and q2 represents the homozygous recessive offspring.

6. Example
A hypothetical population of 10,000 humans has 6840 individuals with the blood type AA, 2860 individuals with blood type AB and 300 individuals with the blood type BB.
What is the frequency of each genotype in this population?
What is the frequency of the A allele?
What is the frequency of the B allele?
If the next generation contained 25,000 individuals, how many individuals would have blood type BB, assuming the population is in Hardy-Weinberg equilibrium?

7. Example
A population of rabbits may be brown (the dominant phenotype) or white (the recessive phenotype). Brown rabbits have the genotype BB or Bb. White rabbits have the genotype bb. The frequency of the BB genotype is 0.35.
What is the frequency of heterozygous rabbits?
What is the frequency of the B allele?
What is the frequency of the b allele?

8. Example
A population of birds contains 16 animals with red tail feathers and 34 animals with blue tail feathers. Blue tail feathers are the dominant trait.
What is the frequency of the red allele?
What is the frequency of the blue allele?
What is the frequency of heterozygotes?
What is the frequency of birds homozygous for the blue allele?

9. Sample Problems & Practice
Page 683 Questions 1-5
Page 684: Applying the Hardy Weinberg Equation
Page 688 Questions 1-8
Practice Problems Worksheet – Next Class.

10. Causes of gene pool change
Mutations
Gene Flow
Non-Random Mating
Genetic Drift
The Founder Effect
The Bottleneck Effect
Natural Selection

11. The BottleNeck Effect
Modelling the bottleneck effect. The parent population contains roughly equal numbers of yellow and blue alleles. A catastrophe occurs and there are only a few survivors. Most of these survivors have blue alleles. Due to genetic drift, the gene pool of the next generation will contain mostly blue alleles.

12. The Founder Effect
The founder effect is a form a genetic drift which occurs when one group was founded by a small group of individuals with unusual genes.
Example: Achromotopsia is a genetic disorder where the retina does not have any cones and, as a result, people with achromotopsia do not have colour vision. Scientists have recently discovered a population of people living on a small Pacific island who have a very high rate of achromotopsia. They suspect that the gene may have been introduced by one Nordic migrant.

13. Sample Problems & Practice
Page 692 Thought Lab 19.1
The Spirit Bear
Page 696 Thought Lab 19.2
Maintaining Genetic Diversity in the Whooping Crane
Page 697 Questions 1-8
Chapter 19 Review: Page Test coming up!

14. Chapter 20: Population Growth and Interactions
Populations always changing in size
Deaths, births
Main determinants (measured per unit time):
Natality = number of births
Mortality = number of deaths
Emigration = # of individuals that move away
Immigration = # of individuals that move into an existing population

15. Population distribution
(A) Golden eagles are territorial, and so pairs are distributed uniformly.
(B) In summer, female moose with calves tend to be distributed randomly over a suitable habitat.
(C) Soapweed yucca can reproduce sexually or asexually by sprouting new plants from the rhizomes (underground stems) of older plants. Therefore, soapweed yucca plants that have reproduced asexually grow in patches, resulting in their clumped pattern of distribution.

16. Effect on Determinants
The determinants vary from species to species
Environmental Conditions
Fecundity
Potential for a species to produce offspring in one lifetime

17. Limits to Fecundity Fertility often less than fecundity
Food availability
Mating success
Disease
Human factors
Immigration
Emigration

18. Calculating Changes in Population Size
Population Change (∆N) = [(births + immigration) – (deaths + emigration)]
- just plug in the values as determined.
2. To calculate the rate of population growth: gr = ∆N/∆t
Snail population in Banff Springs is 3800 in 1997, but falls to 1800 in 1999.
Calculate the growth rate:
gr = /2 years
= snails/year
The population declined at a rate of 1000 snails per year.

19. Calculating Changes in Population Size
3. Calculating the per capita growth rate (cgr): ∆N/N (N= initial pop. size)
cgr = [(birth + immigration) – (deaths + emigration)] x 100 (%) initial population size (n)
Positive Growth: Birth + Immigration > Death + Emigration
Negative Growth: Birth + Immigration <Death + Emigration

20. Population Growth in unlimited environments
Under ideal conditions – no predators and unlimited resources…
A species can reach its biotic potential - the highest possible per capita growth rate for a population.
Factors that determine biotic potential are related to fecundity:
# of offspring per reproductive cycle
# of offspring that survive to reproduce
The age of reproductive maturity
# of times that an individual reproduces in its life span
the life span of the individuals

21. Continued… Exponential Population Growth:
Population grows at its max. biotic potential
Starts with a lag phase and forms a J-shaped curve.
Really only see in lab conditions.

22. Population Growth in limited environments
S-shaped curve (sigmoidal)
3 phases:
Lag (slow growth)
Log (rapid growth)
Stationary (no growth)
At stationary phase, population is in dynamic equilibrium, it will fluctuate around the carrying capacity of its habitat.
carrying capacity changes in response to environmental conditions – resource supply, predation, limited space, disease etc.

23. Continued…

24. Population Growth Models and Life History:
Organisms use strategies to maximize the # of offspring that survive to reproductive age.
Theoretically, the best idea is
reach sexual maturity early
have a long life span
produce large #s of offspring
provide them with high quality care until they can reproduce.
Not realistic…
There are different life strategies which relate to the environment in which the organism lives.
These are known as r-selected or K-selected strategies

25. Continued… r- selected K - selected
Species that have an r-selected strategy live close to their biotic potential.
In general, these organisms:
Have a short life span
Become sexually mature at a young age
Produce large broods of offspring
Provide little or no parental care to their offspring.
Insects, annual plants and algae are examples – take advantage of favorable conditions in the summer – reproduce exponentially, but die at the end of the season.
Organisms with a K-selected strategy live close to the carrying capacity of their habitats.
In general, these organisms:
Have a relatively long life span
Become sexually mature later in life
Produce few offspring per reproductive cycle
Provide a high level of parental care
Mammals and birds are examples of organisms that use this.
Many populations are in-between these strategies and describing a population usually involves a comparison – rabbits could be described as K-selected…compared to mosquitoes. Compared to bears, rabbits are r-selected.

26. Carrying Capacity Factors
Density Dependent
Density Independent
Are biotic
Parasites
Predation
Disease
Are abiotic
Weather
Flood
Fires
Drought

27. Sample Problems & Practice
Page 706 Thought Lab 20.1
Distribution Patterns and Population Size Estimates
Page 711 Practice Questions 1-6
Page 716 Review Questions 1-9

28. Interactions in Ecological Communities

29. Interactions in Ecological Communities
Intraspecific vs Interspecific Competition
Predator Prey Cycles:
An increase in prey increases the resources that are available to the predators (A), so the predator population increases (B). This leads to a reduction in the prey population (C), followed by a reduction in the predator population (D). And the cycle continues.

30. Symbiosis… Examples?

31. Succession
Primary succession is one of two types of biological and ecological succession of plant life, occurring in an environment in which new substrate devoid of vegetation and other organisms usually lacking soil, such as a lava flow or area left from retreated glacier, is deposited.

32. succession
Secondary succession is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat. Examples include areas which have been cleared of existing vegetation (such as after tree-felling in a woodland) and destructive events such as fires

33. Population growth

34. Population Pyramids

35. Calculating Groth
Four major processes that cause changes in population size are the number of births, immigration, the number of deaths, and emigration: ΔN = (b + i) – (d + e).
The rate at which the size of a population changes over a given time interval can be described using the growth rate equation: gr = ΔN ÷ Δt.
Per capita growth rate (cgr) describes the change in the number of individuals of a population over a given time interval in terms of rate of change per individual: cgr = ΔN ÷ N.

36. Sample Problems & Practice
Page 729 Thought Lab 20.3
Testing the Classical Model of Succession
Page 730 Review Questions 1-6
Page 734 Thought Lab 20.5
Population Growth Rates in Different Countries
Page 737 Review Questions 1-4
Chapter 20 Test and Unit Exam Coming Soon!