1. POPULATION DYNAMICS
Chapters 3 and 4
APES

2. Questions to Ask Yourself…
Why do some populations grow to enormous size while other do not?
What causes abrupt population increases or decreases?
How many individuals does it take to make a viable population?
What roles do competition, genetic diversity, and ecological adaptations play in maintaining or reducing wild species?

3. Determining Population Size
Random Sampling
Several plots are randomly chosen, organism is counted and calculate density for each acre of land.
Plots of land for trees
Ponds for fish
Good for populations that cannot move much.
Larger the number of plots sampled and size of plots = more accurate estimates

4. Determining Population Size
Mark & Recapture
Species caught, tagged, released, then caught again. Proportion of marked to unmarked gives estimate
Used for animals mostly

5. Mark & Recapture Lincoln-Petersen Method N= mn r Where…
N= estimate of population size
m= number of individuals caught on first visit
n= number of individuals caught on second visit
r= number of marked individuals caught on 2nd visit
Must assume that…
Population is closed geographically & no immigration or emigration
All organisms are equally likely to be captured
Catching & marking do not affect catchability
Each sample is random
Marks are not lost between sampling occasions

6. Example of Lincoln-Petersen Method of Population Estimation
A biologist wants to estimate the size of a population of turtles in a lake. She captures 10 turtles on her first visit to the lake, and marks their backs with paint. A week later she returns to the lake and captures 15 turtles. Five of these 15 turtles have paint on their backs, indicating that they are recaptured animals. What is the estimated size of the population?
m = #originally marked = 10
n = total # caught in 2nd sample = 15
r = # caught in 2nd sample that were marked = 5
N= mn = 10 x 15 = 30 r

7. Standard Error and 95% Confidence Limits
Standard Error is calculated to determine 95% confidence limits. How close where we to the actual estimate?
This will give an upper and lower limit that the actual population could fall between.
We could say with 95% confidence that the true population size is between the upper and lower limit.
If your # falls outside the range, you are less than 95% accurate.

8. Population Distribution- can have an affect on how population is sampled, which can affect density measurement. Clumped most common because resources are usually clumped.

9. How do populations grow?
1. Exponential Growth
Optimum environmental conditions required
Constant rate of growth per unit time
A.k.a. “geometric growth”
Produces J-curve on graph
dN = rN dt

10. What is one way exponential growth is calculated?
“Rule of 70”
How long does it take a population to double?
Dividing 70 by the annual percentage growth, will give you the doubling time for a population in years.
EX: A population growing at 35% doubles every how many years?
70 ÷ 35 = 2 years
EX: A country growing at 4% per year will double their populations in how many years?
70 ÷ 4 = 17.5 years
Exponential growth is influenced by biotic potential

11. What is biotic potential?
Reproductive rate of an organism
High reproductive rates give species the potential to produce enormous populations very quickly given unlimited resources and no limiting factors.
Affected by…
Age at reproduction
Frequency of reproduction
# of offspring produced
Reproductive life span
Avg. death rate

12. Biotic Potential Problem
A female fly lays an average of 120 eggs each generation. Half of these eggs are female. How many offspring could be created by one female house fly over 7 generations (about 1 year)?
We would be knee deep in houseflies if this really happened.
Why aren’t we knee deep in houseflies?
Generation
Total Population if all females in each generation lay 120 eggs and then die 1
120 2
7.2 x 103 3
4.3 x 105 4
2.5 x 107 5
1.5 x 109 6
9.3 x 1010 7
5.5 x 1012

13. What is another way to determine exponential growth?
Nt=No * ert
Nt = number of individuals at end of time period
No = number of individuals at beginning of time period
e = Euler’s constant (natural log of rt)
r = intrinsic rate of population growth
t = time period

14. See Population Problems WKST for examples…

15. Carrying capacity
Number of individuals that an area can support and still remain healthy.
Represented by “K” on graph
Not fixed value- may vary depending on season.
If drought is present, the CC will likely be lower than in year with good rainfall.
Shows there are limits to growth

16. When CC is exceeded (overshoot), death rate exceeds birth rate
When CC is exceeded (overshoot), death rate exceeds birth rate. Population crashes or experiences “dieback”
Creates pattern of population explosion followed by population crash- irruptive or Malthusian growth.

17. How do populations grow?
2. Logistic Growth
Most pop. grow exponentially then slow as they reach the CC.
Environmental resistance- factors that reduce population growth rates
Produces S-curve on graph

18. REPRODUCTIVE STRATEGIES
r-selected strategists (Malthusian strategies)
Short life
Rapid growth
Early maturity
Many small offspring
Little parental care & protection
Little investment in individual offspring
Adapted to unstable environment
Pioneers, colonizers
Generalists
Prey
Low-trophic level
Insects, rodents, invertebrates, parasites, annual plants
K-selected strategists (logical strategies)
Long life
Slower growth
Late maturity
Fewer large offspring
High parental care & protection
High investment in individual offspring
Adapted to stable environment
Later stages of succession
Specialists
Predators
High trophic level
Elephants, primates, wolves, whales

20. Factors that Regulate Population Growth
Density Independent Factors
Affect the same proportion of the population regardless of the size of the population.
Usually abiotic factors
Changes in normal weather or climate; drought; excess rain; storms; geologic hazards
Can be good- blooming flowers after desert rainfall; fire in grassland; Jack pine must have fires for germination of seeds

21. Factors that Regulate Population Growth
Density Dependent Factors
As population grows, competition increases.
Usually biotic- food, disease, mates
Interspecific- competition between two different species
Predator-prey oscillations
Resource partitioning
Intraspecific- competition between individuals of the same species
Survival of the fittest
Stress/Crowding- stress-related diseases are more prevalent in a weakened population
Reduced fertility, low disease resistance, hypoactivity, hyperactivity, aggression, lack of parental care, cannibalism

22. Factors that Increase or Decrease Populations
Natality, Fecundity, Fertility
Natality- making new offspring by birth, hatching, germination or cloning
Fecundity- physical ability to reproduce
Fertility- measure of actual number of offspring produced.
Those without children may be fecund but not fertile.

23. Factors that Increase or Decrease Populations
2. Immigration
Movement of members into a population.
3. Emigration
Movement of members out of a population

24. Factors that Increase or Decrease Populations
Age
Both Sexes
Male
Female 76 73 79 1 75 72 78 5 71 68 74 10 66 63 69 15 61 58 64 20 57 54 59 25 52 49 55 30 47 44 50 35 43 40 45 38 33 31 36 29 27 23 60 21 19 22 65 17 18 70 14 12 11 9 80 8 7 85 6
4. Mortality- death rate
Determined by dividing the number of organisms that die in a certain time period by the number alive at the beginning of the period.
Life expectancy- probable number of years of survival for an individual of a given age.
Life span- longest period of life reached by a given type of organism.
Life Expectancies in US: Numbers shown are remaining years of life

25. Survivorship
Survivorship- % of a cohort that survives to a certain age.
3 Periods
Pre-reproductive period (0-15 years)
Reproductive period (16-45 years)
Post-reproductive period (46 years-death)

26. 3 patterns of survivorship
1. Type I- Late Loss
Reproduction early in life
Low mortality at birth
High probability of surviving to advanced age
Death rates increase during advanced age
Advances in prenatal care, nutrition, disease prevention, and cures/ immunizations = increased life spans for people.
EX: humans, annual plants, sheep, elephants (K-strategists)

27. 3 patterns of survivorship
2. Type II- Constant Loss
Uniform death rates throughout all age categories
Predation on all age groups primary means of death.
Seen in organisms that reach adult age quickly.
EX: Rodents, perennial plants, songbirds
Also die from accidents, poison, other random acts

28. 3 patterns of survivorship
3. Type III- Early Loss
Large # of offspring
Reproduce for most of lifetime
High infant mortality rate
EX: sea turtles, trees, internal parasites, fish oysters (r-strategists)

29. Age Structure Diagrams
Growing & declining pop. will have very different proportions of individuals in various age classes.

30. Types of Age Structure Diagrams
Expanding Population
Young (pre-reproductive) dominates population
Has population momentum- more children will move up to become reproductive
Potential for rapid increase in birth rates once the youngsters reach reproductive age.
EX: Developing countries- many countries in Africa

31. Types of Age Structure Diagrams
Stable Populations
Birth rates = death rates
All age groups are about equal
EX: Most Western European countries, U.S.

32. Types of Age Structure Diagrams
Declining Populations
Birth rates are lower than death rates
Many more older people who are not reproducing
Population will become much smaller when they die.