1. Chapter 53
Population Ecology

2. Population Ecology
Study of the factors that affect population size and composition.

3. Population
Individuals of a single species that occupy the same area.

4. Population Dynamics

5. Important Characteristics
1. Density 2. Dispersion

6. Density Number of individuals per unit area or volume. Ex:
Diatoms - 5 million/m3
Trees - 5,000/km2
Deer - 4/km2

7. Dispersion Pattern of spacing among individuals. Types: 1. Clumped
2. Uniform
3. Random

9. Clumped Dispersion May result form a patchy environment.
May increase chances for survival.
Ex:
Schooling behavior
Flocks of birds

10. Uniform Dispersion
Often the result of antagonistic interactions between individuals.
Ex:
Territories
Spacing between desert plants

11. Random Dispersion
Often the result of the absence of strong attractions or repulsions between individuals.
Not a common pattern.

12. Demography
The study of the vital statistics that affect population size.
Ex: Birth and Death rates

13. Demographic Factors Age structure of the population.
Birth and Death rates.
Generation time.
Sex ratio and reproductive behavior.

14. Life Tables Mortality summary for a cohort of individuals.
First developed from life insurance studies.

16. Life Tables Show Mortality rate per year. Life span of the organism.
Fecundity (birth rate).

17. Survivorship Curve
Plot of the numbers of a cohort still alive over time.
Curve Types:
Type I
Type II
Type III

19. Type I Low early deaths. High late deaths. Ex: Humans
Other large mammals

20. Type II
Constant death rate.
Ex:
Annual plants
Many invertebrates

21. Type III
High early deaths.
Low late deaths.
Ex:
Trees
Oysters

22. Comment Curve type may change between young and adults.
Ex: Nestlings - Type III Adult Birds- Type II

23. Life History Strategies
Are the product of natural selection.
Can favor
Maximize survival
Maximize reproduction

24. Examples Semelparity – one shot reproduction with many offspring.
Ex. – Salmon, Agave
Iteroparity – repeated reproduction events with a few offspring each time.

25. Life History Strategies
1. "r" or Opportunistic species 2. "k" or Equilibrial species

26. "r" Species
Increase fitness by producing as many offspring as possible.
Do this by:
Early maturation
Many reproductive events
Many offspring

27. Result
Maximize reproduction so that at least a few offspring survive to the next generation.
Most offspring die (Type III curve).

28. "k" Species Increase fitness by having most offspring survive.
Do this by:
High parental care
Late maturation
Few reproduction events
Few offspring.

29. Result Maximize survivorship of each offspring.
Few offspring, but most survive (Type I curve).

30. What is the strategy For a weed? For an endangered species?
For Garden Pests?

31. Population Growth DN/Dt = b - d Where: N= population size t = time
b = birth rate
d = death rate

32. Rate of Increase r = difference between birth rate and death rate.
r = b - d

33. Assignments Read Chapter 53 or 43 in Hillis Chapter 52 – today
Chapter 53 – Mon. 4/28
Labs – Transpiration, Aquatic Productivity

34. Equation:
DN/Dt = rN
N = population size
t = time
r = rate of increase

35. From Calculus The equation DN/Dt = rN becomes: dN/dt = rmax N
rmax = intrinsic rate of increase

36. Exponential Growth dN/dt = rmax N Characteristic of "r" species.
Produces a “J-shaped” growth curve.
Only holds for ideal conditions and unlimited resources.

38. Logistic Growth
dN/dt = rmax N K-N K
K = carrying capacity

39. Result “S-shaped” growth curve. Characteristic of “k" species.
Common when resources are limited.

41. Comment K is not a constant value.
Populations often oscillate around “K” as the environment changes.

43. Additional Comments
Populations often overshoot “K”, then drop back to or below “K”.
The equations are now on the AP formula sheet. Be prepared to use them.

44. Regulation of Population Size
1. Density- Dependent Factors 2. Density- Independent Factors

45. Density-Dependent Affect is related to N.
As N increases, mortality increases.
Ex: Food, nesting space, disease

47. Density-Independent Affect is not related to N.
Mortality not related to population size.
Ex: Weather and climate

48. Population Cycles Cyclic changes in N over time.
Often seen in predator/prey cycles.
Ex: Snowshoe Hare - Lynx

50. Causes Density dependent factors. Chemical cycles.
Saturation strategy to confuse predators.

51. Age Structure Diagrams
Show the percent of a population in different age categories .
Method to get data similar to a Life Table, but at one point in time.

53. Importances
Can be used to predict future population growth trends, especially for long lived species.

54. Exponential Growth
Produces age structures that are a triangle or pyramid shape.

55. Logistic Growth
Produces age structures that have even sizes between most age categories.

56. Declining Populations
Produce age structures with a narrow base and wider middles.

57. Summary Know density and dispersion patterns.
Know Life Tables and survivorship curves.
Be able to contrast and compare “r” and “k” strategies.

58. Summary Know exponential and logistic growth curves and equations.
Know density and density-independent growth factors.