1. 2.6 Changes: Population Dynamics

2. Assessment Statements
2.6.1 Explain the concepts of limiting factors and carrying capacity in the context of population growth.
2.6.2 Describe and explain S- and J- population curves.
2.6.3 Describe the role of density-dependent and density-independent factors, and internal and external factors, in the regulation of populations.
2.6.4 Describe the principles associated with survivorship curves including, K- and r-strategists.

3. Population Dynamics
Changes in population size and the factors that regulate populations over time.

4. Population Density The number of individuals per unit area/volume.
Example: The number of oak trees per km2 in a forest.

5. Estimation of Population Size
1. Individual counts (not always practical)
2. Transects or Quadrats
3. Mark-recapture method: Lincoln Index
N= marked individual X total catch second time recaptured marked individuals
Example: pond turtles
1992: 18
1993: 34 (12)
1994: 30 (18)

6. Estimation of Population Size
Example: pond turtles 1992: 18
1993: 34 (12)
1994: 30 (18)
: N = 18(34) = 51 turtles 12
_________________________________________
: N = 34(30) = 56.7 turtles 18
So: = = 53.9 turtle estimation 2

7. Dispersion
The distribution of individuals within geographical population boundaries.
Three examples of dispersion patterns:
1. Clumped
2. Uniform
3. Random

8. Dispersion Patterns
1. Clumped a. individuals are aggregated in patches b. unequal distribution of resources in the environment. Example: trees around a lake or pond

9. Dispersion Patterns 2. Uniform a. individuals are evenly distributed
b. interactions among individuals of a population
Example: creosote bushes in the desert

10. Dispersion Patterns 3. Random a. unevenly distributed
b. random dispersion is rare
Example: clams in a mud flat

11. Understanding Population Growth
Exponential Growth Model
Exponential growth: The rate of expansion (growth) of a population under ideal conditions.

12. Exponential Growth – J Curve
Example: bacteria
Number of
individuals
(N)
Time
produces a J-shaped curve

13. Understanding Population Growth
2. Logistic Growth Model logistic growth: environmental factors that restrict the growth of a population (called: population limiting factors)

14. K: Carrying Capacity
The maximum stable population size that a particular environment can support over a relatively long period of time (K).

15. Logistic Growth: S-Curve
Example: turtles in a pond K
Number of
individuals
(N)
Time
produces a S-shaped curve

16. Draw an s-curve and draw a j-curve
Label each

17. Question What if? N, the number of individuals = almost 0:
exponential growth
N, the number of individuals = almost K (carrying capacity):
growth rate is approaching zero Zero Population Growth

18. Factors That Limit Population Growth
1. Density-Dependent Factors:
Population-limiting factors whose effects depend on population density.
The greater the pop, the greater the effects. (negative feedback)
Examples:
1. Limited food supply (competition)
2. Disease
3. Predation/parasitism
4. War

19. Factors That Limit Population Growth
2. Density-Independent Factors:
Population-limiting factors (abiotic) whose occurrence is not affected by pop density.
Increases death rate & decreases birth rate
Affects depend on severity of the event
Examples: 1. Earthquakes
2. Fires
3. Hurricanes
4. Freeze in the fall

20. number of individuals in pop.
Boom and Bust Species
A rapid increase (boom) in a population followed by a sharp decline (bust).
Examples:
a. Daphnia in a pond
number of individuals in pop.
Time
boom
bust

21. Boom and Bust Species
Sometimes species (carnivore) depend on other species (prey) for food.
Example: Snowshoe hare and lynx
number of individuals in pop.
Years

22. Survivorship Curves Life History:
Series of events from birth through reproduction to death.
Two basic types of life history strategies:
1. Opportunistic life history
(r-strategist species)
2. Equilibrial life history – limited by carrying capacity(K)
(K-Strategist species)

23. Opportunistic life history (r-strategist species)
Characteristics:
1. maturing time: short
2. life span: short
3. mortality rate: often high
4. times female is reproductive: usually once
5. age at first reproduction: early
6. size of offspring: small
7. parental care: none
8. Size of organism: small

24. Equilibrial life history (K-strategist species)
Characteristics:
1. maturing time: long
2. life span: long
3. mortality rate: often low
4. times female is reproductive: often many
5. age at first reproduction: late
6. size of offspring: large
7. parental care: often extensive
8. Size of organism: tend to be large

25. Life History Examples
R-strategist species: 1. Garden weeds 2. Insects 3. Desert flowers K-strategist species: 1. Humans 2. Apes 3. Elephants

26. Survivorship Curves Type 1 survivorship curve:
High survival rates until old age.
K or r strategist? K
% of survivors
% of maximum life span
Example?
humans

27. Survivorship Curves Type 3 survivorship curve:
High mortality rates as young but decreased mortality at later ages.
K or r strategist?
% of survivors
% of maximum life span r
Examples?
turtles
oysters
frogs
insects

28. Survivorship Curves Type 2 survivorship curve:
Intermediate between the extremes.
Example
% of survivors
% of maximum life span
squirrel

29. Human Population Growth
Age structure
Proportions of individuals of a population in different age groups.
A typical population has three main age groups (age structure).
1. Pre-reproductive (youth)
2. Reproductive
3. Post-reproductive

30. Age Structure
Post-reproductive
Reproductive
Pre-reproductive

31. Human Population Growth Today
Human population as a whole is growing exponentially.
Has doubled (doubling-time) three times in the last three centuries (doubled the carrying capacity several times).
Is now 7 billion, might reach ~8 billion by 2020.

32. Question: What are the reasons for the increase in human population?
Answer:
1. Improved health
2. Technology
3. Decreased death rates

33. Question: What is Zero Population Growth (ZPG)? Answer:
a. birth rate equals death rate.
b. intrinsic growth (r) = 0

34. Question:
What are two ways the human population can reach Zero Population Growth?
1. Limit the # of offspring per couple
a. Reduces family size
b. Voluntary contraception
c. Family planning
2. Delay reproduction
(late 20’s instead of early 20’s)

35. Question:
What will happen to human’s if the population continues to grow at this rate?
Is there a limit to human population growth? Why/why not?
What EVS does your argument support? Explain