1. You will explain how populations grow.
What You’ll Learn
You will explain how populations grow.
You will identify factors that inhibit the growth of populations.
You will summarize issues in human population growth.
Chapter Intro-page 90

2. 4.1 Section Objectives – page 91
Compare and contrast exponential and linear population growth.
Relate the reproductive patterns of different populations of organisms to models of population growth.
Predict effects of environmental factors on population growth.
4.1 Section Objectives – page 91

3. Section 4.1 Summary – pages 91-99
Principles of Population Growth
A population is a group of organisms, all of the same species, that live in a specific area.
A healthy population will grow and die at a steady rate unless it runs out of food or space, or is attacked in some way by disease or predators.
Scientists study changes in populations in a variety of ways.
Section 4.1 Summary – pages 91-99

4. Section 4.1 Summary – pages 91-99
Principles of Population Growth
One method involves introducing organisms into an environment that contains abundant resources and then watching how the organisms react.
Section 4.1 Summary – pages 91-99

5. Section 4.1 Summary – pages 91-99
Principles of Population Growth
Studies of populations of larger organisms, such as an elk population in a national park, require methods such as the use of radio monitors.
Section 4.1 Summary – pages 91-99

6. Section 4.1 Summary – pages 91-99
How fast do populations grow?
The growth of populations is unlike the growth of pay you get from a job.
Populations of organisms, do not experience linear growth. Rather, the graph of a growing population starts out slowly, then begins to resemble a J-shaped curve.
Section 4.1 Summary – pages 91-99

7. Section 4.1 Summary – pages 91-99
How fast do populations grow?
Population Growth of Houseflies
1 million
Population size
500,000
100
One year
Section 4.1 Summary – pages 91-99

8. Section 4.1 Summary – pages 91-99
How fast do populations grow?
The initial increase in the number of organisms is slow because the number of reproducing individuals is small.
Soon, however, the rate of population growth increases because the total number of individuals that are able to reproduce has increased.
Section 4.1 Summary – pages 91-99

9. Section 4.1 Summary – pages 91-99
Is growth unlimited?
A J-shaped growth curve illustrates exponential population growth.
Exponential growth means that as a population gets larger, it also grows at a faster rate.
Exponential growth results in unchecked growth.
Section 4.1 Summary – pages 91-99

10. Section 4.1 Summary – pages 91-99
What can limit growth?
Limiting factors, such as availability of food, disease, predators, or lack of space, will cause population growth to slow.
Under these pressures, the population may stabilize in an S-shaped growth curve.
Section 4.1 Summary – pages 91-99

11. Section 4.1 Summary – pages 91-99
What can limit growth?
Characteristics of Population Growth
Exponential growth
PREDA-TORS
DISEASE
SPACE
FOOD
Carrying capacity
J curve
S curve
Population
Time
Section 4.1 Summary – pages 91-99

12. Section 4.1 Summary – pages 91-99
Carrying capacity
The number of organisms of one species that an environment can support indefinitely is its carrying capacity.
When a population overshoots the carrying capacity, then limiting factors may come into effect.
Click image to view movie.
Section 4.1 Summary – pages 91-99

13. Section 4.1 Summary – pages 91-99
Carrying capacity
Deaths begin to exceed births and the population falls below carrying capacity.
Carrying capacity
Section 4.1 Summary – pages 91-99

14. Section 4.1 Summary – pages 91-99
Reproduction Patterns
In nature, animal and plant populations change in size.
Biologists study the factor that determines population growth—an organism’s reproductive pattern, also called its life-history pattern.
A variety of population growth patterns are possible in nature.
Section 4.1 Summary – pages 91-99

15. Section 4.1 Summary – pages 91-99
Rapid life-history patterns
Rapid life-history patterns are common among organisms from changeable or unpredictable environments.
Rapid life-history organisms have a small body size, mature rapidly, reproduce early, and have a short life span.
Section 4.1 Summary – pages 91-99

16. Section 4.1 Summary – pages 91-99
Slow life-history patterns
Large species that live in more stable environments usually have slow life-history patterns.
Section 4.1 Summary – pages 91-99

17. Section 4.1 Summary – pages 91-99
Slow life-history patterns
Slow life-history organisms reproduce and mature slowly, and are long-lived. They maintain population sizes at or near carrying capacity.
Section 4.1 Summary – pages 91-99

18. Section 4.1 Summary – pages 91-99
Density factors and population growth
How organisms are dispersed can be important.
Three patterns of dispersal are random, clumped, and uniform.
Random
Clumped
Uniform
Section 4.1 Summary – pages 91-99

19. Section 4.1 Summary – pages 91-99
Density factors and population growth
Ecologists have identified two kinds of limiting factors that are related to dispersal: density-dependent and density-independent factors.
Population density describes the number of individuals in a given area.
Section 4.1 Summary – pages 91-99

20. Section 4.1 Summary – pages 91-99
Density factors and population growth
Density-dependent factors include disease, competition, predators, parasites, and food.
Disease, for example, can spread more quickly in a population with members that live close together.
Section 4.1 Summary – pages 91-99

21. Section 4.1 Summary – pages 91-99
Density factors and population growth
Density-independent factors can affect all populations, regardless of their density.
Most density-independent factors are abiotic factors, such as temperature, storms, floods, drought, and major habitat disruption.
Section 4.1 Summary – pages 91-99

22. Section 4.1 Summary – pages 91-99
Organism Interactions Limit Population Size
Population sizes are limited not only by abiotic factors, but also are controlled by various interactions among organisms that share a community.
Section 4.1 Summary – pages 91-99

23. Section 4.1 Summary – pages 91-99
Predation affects population size
When a predator consumes prey on a large enough scale, it can have a drastic effect on the size of the prey population.
Populations of predators and their prey are known to experience cycles or changes in their numbers over periods of time.
Section 4.1 Summary – pages 91-99

24. Section 4.1 Summary – pages 91-99
Predation affects population size
The data in this graph reflect the number of hare and lynx pelts sold to the Hudson’s Bay Company in northern Canada from 1845 through 1935.
Lynx and Hare Pelts Sold to the Hudson’s Bay Company
Lynx
Hare
Number of organisms(in thousands)
Times (in years)
Section 4.1 Summary – pages 91-99

25. Section 4.1 Summary – pages 91-99
Predation affects population size
In field studies, predation increases the chance that resources will be available for the remaining individuals in a prey population.
Section 4.1 Summary – pages 91-99

26. Section 4.1 Summary – pages 91-99
Competition within a population
Competition is a density-dependent factor.
When only a few individuals compete for resources, no problem arises.
When a population increases to the point at which demand for resources exceeds the supply, the population size decreases.
Section 4.1 Summary – pages 91-99

27. Section 4.1 Summary – pages 91-99
The effects of crowding and stress
When populations of certain organisms become crowded, individuals may exhibit symptoms of stress.
As populations increase in size in environments that cannot support increased numbers, individual animals can exhibit a variety of stress symptoms.
Section 4.1 Summary – pages 91-99

28. Section 4.1 Summary – pages 91-99
The effects of crowding and stress
These include aggression, decrease in parental care, decreased fertility, and decreased resistance to disease.
They become limiting factors for growth and keep populations below carrying capacity.
Section 4.1 Summary – pages 91-99

29. Question 1 A. grows at a slower rate B. grows at a faster rate
Exponential growth means that as a population gets larger, it also _____.
A. grows at a slower rate
B. grows at a faster rate
C. grows at a steady rate
D. stabilizes in an S-shaped growth curve
Section 1 Check

30. Population Growth of Houseflies
The answer is B. A J-shaped growth curve illustrates exponential growth.
Population Growth of Houseflies
1 million
Population size
500,000
100
One year
Section 1 Check

31. Question 2 A. population increases exponentially
Which of the following would you expect to observe after a population exceeds its carrying capacity?
A. population increases exponentially
B. births exceed deaths
C. deaths exceed births
D. population growth rate is unaffected by limiting factors
Section 1 Check

32. Characteristics of Population Growth
The answer is C. Limiting factors may come into effect after a population exceeds its carrying capacity. Deaths begin to exceed births and the population falls below carrying capacity.
Characteristics of Population Growth
Exponential growth
DISEASE
SPACE
PREDATORS
FOOD
Carrying capacity
J curve
S curve
Population
Time
Section 1 Check

33. Question 3 Organism Offspring per Individual Life Span
mosquito
250
1 month
elephant 5
70 years
humans 2
77 years
oak tree 50
100 years
A. grows at a slower rate
B. grows at a faster rate
C. grows at a steady rate
D. stabilizes in an S-shaped growth curve
Section 1 Check

34. Offspring per Individual Life Span
The answer is A. Rapid life-history organisms have a small body size, mature rapidly, reproduce early, and have a short life span.
Organism
Offspring per Individual
Life Span
mosquito
250
1 month
elephant 5
70 years
humans 2
77 years
oak tree 50
100 years
Section 1 Check

35. Question 4 A. life-history pattern B. growth rate C. demographic
The number of organisms of one species that an environment can support indefinitely is its _____.
A. life-history pattern
B. growth rate
C. demographic
D. carrying capacity
Section 1 Check

36. The answer is D. If population size rises above the carrying capacity, more organisms die than are born and the population drops back below the carrying capacity.
Carrying capacity
Section 1 Check

37. Question 5
Compare the terms “density-dependent factors” and “density-independent factors”.
Section 1 Check

38. Both are limiting factors for organisms
Both are limiting factors for organisms. Density-dependent factors have an increasing effect as the population increases and include disease, competition, parasites, and food. Density-independent factors can affect all populations regardless of density. Most are abiotic factors such as temperature, rainfall, and major habitat destruction.
Section 1 Check

39. 4.2 Section objectives– page 100
Identify how the birthrate and death rate affect the rate at which a population changes.
Compare the age structure of rapidly growing, slow-growing, and no-growth countries.
Explain the relationship between a population and the environment.
4.2 Section objectives– page 100

40. Section 4.2 Summary – page 100-103
World Population
In the United States, a census is taken every ten years.
One of the most useful pieces of data is the rate at which each country’s population is growing or declining.
These figures are the basis for demography, the study of human population size, density and distribution, movement, and its birth and death rates.
Section 4.2 Summary – page

41. Section 4.2 Summary – page 100-103
Human population growth
Human population growth is different because humans have the ability to change their environment.
People live longer and are able to produce offspring that live long enough to produce offspring, hence, a population grows.
Section 4.2 Summary – page

42. Section 4.2 Summary – page 100-103
Calculating growth rate
There are a number of factors that determine population growth rate.
These are births, deaths, immigration and emigration.
Birthrate is the number of live births per 1000 population in a given year.
Section 4.2 Summary – page

43. Section 4.2 Summary – page 100-103
Calculating growth rate
Death rate is the number of deaths per 1000 population in a given year.
Movement of individuals into a population is immigration.
Section 4.2 Summary – page

44. Section 4.2 Summary – page 100-103
Calculating growth rate
Movement out of a population is emigration.
Birthrate – Death rate = Population Growth Rate (PGR)
If the birth rate of a population equals its death rate, then the population growth rate is zero.
Section 4.2 Summary – page

45. Section 4.2 Summary – page 100-103
Calculating growth rate
If the PGR is above zero, more new individuals are entering the population than are leaving, so the population is growing.
A PGR can also be less than zero.
Section 4.2 Summary – page

46. Section 4.2 Summary – page 100-103
Doubling time
Another quantitative factor that demographers look at is the doubling time of a population.
Doubling time is the time needed for a population to double in size.
The time it takes for a population to double varies depending on the current population and growth rate.
Section 4.2 Summary – page

47. Section 4.2 Summary – page 100-103
Doubling time
Doubling time can be calculated for the world, a country, or even a small region, such as a city.
Section 4.2 Summary – page

48. Section 4.2 Summary – page 100-103
Age structure
Population Distribution Per Age Range for Several Countries
Stable growth
Rapid growth
Slow growth
Male
Reproductive years
Female
Age
Population (percent of total for each country)
Section 4.2 Summary – page

49. Section 4.2 Summary – page 100-103
Ecology and growth
The needs of populations differ greatly throughout the world.
Sometimes, a population grows more rapidly than the available resources can handle.
Section 4.2 Summary – page

50. Section Summary – page 100-103
Ecology and growth
Resources that are needed for life, such as food and water, become scarce or contaminated.
Section Summary – page

51. Section Summary – page 100-103
Ecology and growth
The amount of waste produced by a population becomes difficult to dispose of properly.
These conditions can lead to stress on current resources and contribute to the spread of diseases that affect the stability of human populations both now and to come.
Section Summary – page

52. Question 1 A. ecology B. demography C. phylogeny D. biodiversity
What is the study of human population size, density and distribution, movement, and birth and death rates called?
A. ecology
B. demography
C. phylogeny
D. biodiversity
Section 2 Check

53. The answer is B. When various demographic data are monitored, societies are able to improve environmental conditions and quality of life.
Section 2 Check

54. Question 2 Year Birthrate Death rate 1 270 170 2 250 190 3 390 370
A. Growing at a greater rate each year
B. Declining at a greater rate each year
C. Growing at a decreasing rate each year
D. Declining at a decreasing rate each year
Section 2 Check

55. The answer is C. In each of these years, the population growth rate is above zero, but is decreasing.
Year
Birthrate
Death rate 1
270
170 2
250
190 3
390
370
Section 2 Check

56. Question 3
Which interval in the diagram below represents the population reaching equilibrium near carrying capacity?
A. 1
B. 2
C. 3
D. 4
Section 2 Check

57. The answer is D. The number of organisms tends to rise above and fall below the carrying capacity due to limiting factors.
Section 2 Check

58. Population Dynamics
Populations of some organisms do not exhibit linear growth. If there is nothing to stop or slow growth, a population’s growth appears as a J-shaped curve on a graph.
Populations grow slowly at first, then more rapidly as more and more individuals begin to reproduce.
Chapter Summary – 4.1

59. Population Dynamics
Under normal conditions, with limiting factors, populations show an S-shaped curve as they approach the carrying capacity of the environment where they live.
Chapter Summary – 4.1

60. Population Dynamics
If a population overshoots the environment’s carrying capacity, deaths exceed births and the total population falls below the environment’s carrying capacity. The number of individuals will fluctuate above and below the carrying capacity.
Chapter Summary – 4.1

61. Population Dynamics
Density-dependent factors and density-independent factors affect population growth. Density-dependent factors include disease, competition for space, water, and food supply. Density-independent factors are volcanic eruptions and changes in climate that result in catastrophic incidents such as floods, drought, hurricanes, or tornadoes.
Chapter Summary – 4.1

62. Human Population
Demography is the study of population characteristics such as growth rate, age structure, and movement of individuals.
Birthrate, death rate, immigration, emigration, doubling time, and age structures differ considerably among different countries. There are uneven population growth patterns throughout the world.
Chapter Summary – 4.2

63. Question 1
Chapter Assessment

64. The answer is B. The graph of exponential growth is a J-shaped curve.
Chapter Assessment

65. Question 2
What shape of age structure graph represents a rapidly growing population?
A. steep triangle
B. thin rectangle
C. circle
D. square
Chapter Assessment

66. The answer is A.
Population Distribution Per Age Range for Several Countries
Stable growth
Rapid growth
Slow growth
Male
Reproductive years
Female
Age
Population (percent of total for each country)
Chapter Assessment

67. Question 3 What type of growth is shown in this graph?
Population Growth of Houseflies
1 million
What type of growth is shown in this graph?
500,000
Population size
100
One year
A. slowly increasing
C. exponential
B. slowly decreasing
D. equilibrium
Chapter Assessment

68. The answer is C. Exponential growth is rapid and is represented on a graph by a J-shaped curve.
Population Growth of Houseflies
1 million
500,000
Population size
100
One year
Chapter Assessment

69. Question 4
Assume that each time interval on the graph is equal to one year. How long did it take this population to reach carrying capacity?
Characteristics of Population Growth
A. 2 years
Exponential growth
SPACE
PREDATORS
DISEASE
FOOD
B. 4 years
Carrying capacity
C. 5 years
J curve
S curve
Population
D. 9 years
Time
Chapter Assessment

70. The answer is D. After 9 years, this population has nearly reached carrying capacity.
Characteristics of Population Growth
Exponential growth
PREDA-TORS
FOOD
DISEASE
SPACE
Carrying capacity
J curve
S curve
Population
Time
Chapter Assessment

71. Question 5
Which of the following is characteristic of a species having a slow life-history pattern?
A. short life span
B. long life span
C. small body size
D. mature rapidly
Chapter Assessment

72. The answer is B. Rapid life-history organisms have a small body size, short life span, and mature rapidly.
Chapter Assessment

73. Question 6
During which time period was population growth the most rapid?
A to 1930
B to 1960
Chapter Assessment

74. Question 6
During which time period was population growth the most rapid?
C to 1975
D to 1987
Chapter Assessment

75. The answer is D. World population grew by 1 billion in just 12 years.
Chapter Assessment

76. Question 7
If the birthrate is 125 and the death rate is 135, what is the population growth rate?
A. 260
B. -260
C. 10
D. -10
Chapter Assessment

77. The answer is D. Use the formula:
Birthrate – Death rate = Population Growth Rate
Chapter Assessment

78. Carolina Biological Supply Co. Digital Stock Matt Meadows PhotoDisc
Photo Credits
Corbis
Carolina Biological Supply Co.  
Digital Stock
Matt Meadows
PhotoDisc
Alton Biggs
Chapter Assessment

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