2. Chapter 4.1
Population Ecology

3. Population Characteristics
Population Density: The number of living entities per unit of area

5. Population Characteristics
Spatial Dispersion: the pattern of spacing of a population within an area
Uniform
Clumped (groups or herds)
Random
Dispersion patterns depend on the availability of resources

7. Limiting Factors
Limiting Factors: any abiotic or biotic factor that restricts the number, reproduction, or distribution of organisms

8. Limiting Factors Two types of limiting factors: Density independent
Density dependent

9. Chapter 4
Population Ecology
4.1 Population Dynamics
Density-independent factor: Any factor (that limits population size) in an environment that does not depend on the number of members in a population per unit area.

10. Examples?

11. Density-Independent Factors
Weather events – rainfall, flood, acidity, drought
Fire
Human alterations of the landscape
Air, land, and water pollution

12. Can wipe out populations of species regardless if there are a few or a lot in a given area
Density independent factors
are unaffected by the number of
individuals in a given area

13. The greater the number of species, the more that are wiped out
Chapter 4
Population Ecology
4.1 Population Dynamics
Density-dependent factor: Any factor, that limits population size, in an environment that depends on the number of members in a population per unit area
The greater the number of species, the more that are wiped out

14. Examples?

15. Density-Dependent Factors
Usually biotic factors and may include:
Disease
Parasites
Competition for resources
Predation

16. Density dependent factors are directly affected by the density of individuals in a given area.

17. Density-Dependent Factors
Example:
If one deer in a heavily populated community contracts tuberculosis, a communicable disease, what will happen to the deer population?
Parasite?

18. Examples of Density-Dependent Factors:
Competition: for food, space, mates
Causes a lower birth rate (natality), increases death rate (mortality), or both

19. Density-Dependent Factors
Predation: interaction between species on different trophic levels
Almost every species is food for another species
Predators (hunters) and prey (the hunted) have, in most cases, existed together for years

20. Predator-Prey Graph

22. What do you notice about the populations?

23. Population Growth Rate
Chapter 4
Population Ecology
4.1 Population Dynamics
Population Growth Rate
Population growth rate (PGR) explains how fast a given population grows.
What are some factors that would affect how quickly a populations grow?

24. Population Growth Rate
Depends on several factors:
Natality: birthrate (during a given time)
Mortality: death rate (during the same given time)
These two factors affect PGR the most

25. Emigration: the number of individuals moving away from a population
Immigration: the number of individuals moving into a population
These two factors are usually about the same

26. Two mathematical models that represent population growth rate:
1. Exponential Growth Model
2. Logistic Growth Model

27. Exponential Growth Model
Chapter 4
Population Ecology
4.1 Population Dynamics
Exponential Growth Model
Exponential growth : the growth rate is proportional to the size of the population.
All populations grow exponentially until
some limiting factor slows the population’s
growth.

28. If all offspring survive and reproduce, the population grows slowly at first
Lag phase: slow growth period

29. The rate of population growth begins to increase rapidly
Exponential growth phase: rapid population growth due to total number of organisms without any limiting factors
Exponential growth creates a J-shaped curve

30. Second Model: Logistic Growth Model

31. Chapter 4
Population Ecology
4.1 Population Dynamics
Logistic Growth Model
The population’s growth slows or stops following exponential growth, at the population’s carrying capacity.

32. Carrying capacity: the maximum number of organisms in a population that an environment can support for the long term
Carrying capacity is limited by the energy, water, oxygen, and nutrients available (resources).

33. Logistic Growth Model

34. Logistic Growth Model
Similar to the exponential growth model, but with an S-shaped curve
Occurs when the population’s growth slows or stops after exponential growth at the population’s carrying capacity

35. Chapter 4
Population Ecology
4.1 Population Dynamics
Exceeding the carrying capacity of an area results in death to the organisms living there

36. Boom and Bust Graph

37. A = exponential growth
B = massive death
C = “new” carrying capacity

38. Reproductive Patterns
Chapter 4
Population Ecology
4.1 Population Dynamics
Reproductive Patterns
Species vary in the number of births per reproduction cycle, in the age that reproduction begins, and in the life span of the organism.
Two main patterns:
R-strategy
K-strategy

39. An r-strategist is generally a small organism.
Chapter 4
Population Ecology
4.1 Population Dynamics
R-strategy: (Rate Strategy) is a population pattern seen where fluctuations in biotic or abiotic factors occur in the environment.
An r-strategist is generally a small organism.
Short life span
Produces many offspring

40. Examples of r-strategists:
Fruit fly
Mice
Locusts

41. A k-strategist is generally a larger organism.
Chapter 4
Population Ecology
4.1 Population Dynamics
k-strategy : (carrying-capacity strategy) a population reproduction pattern that is adapted for living in stable environments.
A k-strategist is generally a larger organism.
Long life span
Produces few offspring

42. Examples:
Bears
Elephants

43. Factors that Contribute to Biotic Potential
Low (few babies)
k-strategists
High (lots of babies) r-strategists
Maternal age
older
younger
Number of offspring
1-2 (low)
1,000s (high)
Maternal care
months/years
short/none
Gestation period
long
short
Organism’s size
large
small

44. Human Population 4.2

45. Chapter 4
Population Ecology
4.2 Human Population
Human Population Growth
Demography: The study of human population size, density, distribution, movement, and birth and death rates.

46. Technological Advances
Chapter 4
Population Ecology
4.2 Human Population
Technological Advances
For thousands of years, the size of the human population remained relatively constant and below the environment’s carrying capacity.
Why is it increasing in population now?

47. Populations are Increasing Because:
Advances in technology:
Farming and domestication of animals
Medicine—antibiotics and vaccines
Better shelter

48. Human Population Growth Rate
Chapter 4
Population Ecology
4.2 Human Population
Human Population Growth Rate
Although the human population is still growing, the rate of its growth has slowed.

49. What might have happened in the 1960s?
What might be responsible for the decline in percent increase in human population (world wide)?

50. Trends in Human Population Growth
Chapter 4
Population Ecology
4.2 Human Population
Trends in Human Population Growth
Population trends can be altered by events such as disease and war.
Human population
growth is not the same in all countries.
Why not?

51. Demographic Transition
Demographic Transition: a change in growth rate resulting from high birth and death rates to low birth and death rates
Consists of 3 stages

52. Most countries have not yet undergone a complete demographic transition
80% of the world’s population lives in these areas

53. Stage 1: high birth rate and a high death rate
Families have lots of children

54. Stage 2: Improvements in living conditions
Increased food production
Medical advances
Improved sanitation

55. Stage 3: The birth rate decreases
Families have fewer children
Population growth slows and may stabilize
Undergone an industrial revolution

56. Future population growth depends somewhat on how many people of different ages are living in that country today.

57. Zero Population Growth
Chapter 4
Population Ecology
4.2 Human Population
Zero Population Growth
Zero population growth (ZPG) occurs when the birthrate and immigration rate equal the deathrate and emigration rate.

59. pre-reproductive stage, reproductive stage, and post-
Chapter 4
Population Ecology
4.2 Human Population
Age Structure
Age structure: the number of males and females in each of three age groups:
pre-reproductive stage, reproductive stage, and post-
reproductive stage.

61. At zero population growth, an age structure graph should appear more balanced with numbers at pre-reproductive, reproductive, and post-reproductive ages being approximately equal.

62. Human Carrying Capacity
Chapter 4
Population Ecology
4.2 Human Population
Human Carrying Capacity
Scientists are concerned about the human population reaching or exceeding the carrying capacity.
An important factor is the amount of resources from the biosphere that are used by each person.