1. Chapter 36
Population Ecology

2. Populations are described by their boundaries and size
Population ecology is the study of populations in relation to their environment, including environmental influences on density and distribution, age structure, and population size
A population is a group of individuals of a single species living in the same general area
Populations are described by their boundaries and size
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3. Density and Dispersion
Density is the number of individuals per unit area or volume
Dispersion is the pattern of spacing among individuals within the boundaries of the population
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4. Density: A Dynamic Perspective
In most cases, it is impractical or impossible to count all individuals in a population
Immigration is the influx of new individuals from other areas
Emigration is the movement of individuals out of a population
Sampling techniques - Population size can be estimated by either extrapolation from small samples, an index of population size (e.g., number of nests), or the mark-recapture method
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5. Deaths and emigration remove individuals from a population.
Figure 53.3
Births
Deaths
Deaths and emigration remove individuals from a population.
Births and immigration add individuals to a population.
Figure 53.3 Population dynamics.
Immigration
Emigration 5

6. Patterns of Dispersion
Figure 53.4
(a) Clumped
Patterns of Dispersion
(b) Uniform
Figure 53.4 Patterns of dispersion within a population’s geographic range.
(c) Random 6

7. Most organisms exhibit a clumped dispersion pattern (i. e
Most organisms exhibit a clumped dispersion pattern (i.e. herds, packs, etc).
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8. Figure 53.4a
(a) Clumped
Figure 53.4 Patterns of dispersion within a population’s geographic range. 8

9. A uniform dispersion is one in which individuals are evenly distributed
It may be influenced by social interactions such as territoriality, the defense of a bounded space against other individuals
Plants – secrete toxins into soil to prevent growth of neighboring plants within a certain distance. (ie. Sage plant)
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10. Figure 53.4b
(b) Uniform
Figure 53.4 Patterns of dispersion within a population’s geographic range. 10

11. It occurs in the absence of strong attractions or repulsions
In a random dispersion, the position of each individual is independent of other individuals
It occurs in the absence of strong attractions or repulsions
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12. Figure 53.4c
(c) Random
Figure 53.4 Patterns of dispersion within a population’s geographic range. 12

13. Demographics
Demography is the study of the vital statistics of a population and how they change over time
Death rates and birth rates are of particular interest to demographers
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14. Table 53.1
Table 53.1 Life Table for Belding’s Ground Squirrels (Spermophilus beldingi) at Tioga Pass, in the Sierra Nevada of California 14

15. Survivorship Curves
A survivorship curve is a graphic way of representing the data in a life table
The survivorship curve for Belding’s ground squirrels shows a relatively constant death rate
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16. Number of survivors (log scale)
Figure 53.5
1,000
100
Number of survivors (log scale)
Females 10
Males
Figure 53.5 Survivorship curves for male and female Belding’s ground squirrels. 1 2 4 6 8 10
Age (years) 16

17. 3 Types of Survivorship Curves:
Type I: low death rates during early and middle life and an increase in death rates among older age groups
Type II: a constant death rate over the organism’s life span
Type III: high death rates for the young and a lower death rate for survivors
Many species are intermediate to these curves
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18. Number of survivors (log scale)
Figure 53.6
1,000 I
100 II
Number of survivors (log scale) 10
Figure 53.6 Idealized survivorship curves: Types I, II, and III.
III 1 50
100
Percentage of maximum life span 18

19. Measuring Population Growth Rates
Change in
population
size
Births
Immigrants
entering
Deaths
Emigrants
leaving   
For measuring GLOBAL changes - immigration and emigration are ignored, a population’s growth rate equals birth rate minus death rate ONLY!
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20. Exponential Growth Model
Exponential population growth is population increase under idealized condition
Idealized situations help us understand the capacity of species to increase and the conditions that may facilitate this growth
Exponential population growth results in a J-shaped curve
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21. 2,000 dN dt = 1.0N 1,500 dN dt = 0.5N Population size (N) 1,000 500 5
Figure 53.7
2,000
dN dt
= 1.0N
1,500
dN dt
= 0.5N
Population size (N)
1,000
500
Figure 53.7 Population growth predicted by the exponential model. 5 10 15
Number of generations 21

22. Figure 53.8
8,000
6,000
Elephant population
4,000
2,000
Figure 53.8 Exponential growth in the African elephant population of Kruger National Park, South Africa.
1900
1910
1920
1930
1940
1950
1960
1970
Year
The elephant population in Kruger National Park, South Africa, grew exponentially after hunting was banned 22

23. Exponential growth cannot be sustained for long in any population
The logistic model describes how a population grows more slowly as it nears its carrying capacity
Exponential growth cannot be sustained for long in any population
A more realistic population model limits growth by incorporating carrying capacity
Carrying capacity (K) is the maximum population size the environment can support
Carrying capacity varies with the abundance of limiting resources
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26. The Logistic Growth Model
In the logistic population growth model, the per capita rate of increase declines as carrying capacity is reached
The logistic model of population growth produces a sigmoid (S-shaped) curve
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27. ( ) Exponential growth 2,000 dN dt = 1.0N 1,500 K = 1,500
Figure 53.9
Exponential growth
2,000 dN dt
= 1.0N
1,500
K = 1,500
Logistic growth dN dt (
1,500 – N
1,500 )
Population size (N)
= 1.0N
1,000
Figure 53.9 Population growth predicted by the logistic model.
Population growth begins slowing here.
500 5 10 15
Number of generations 27

28. Number of Paramecium/mL
Figure 53.10
1,000
180
150
800
Number of Daphnia/50 mL
120
Number of Paramecium/mL
600 90
400 60
200 30 5 10 15 20 40 60 80
100
120
140
160
Figure How well do these populations fit the logistic growth model?
Time (days)
Time (days)
(a) A Paramecium population in the lab
(b) A Daphnia population in the lab 28

29. Many factors that regulate population growth are density dependent
There are two general questions about regulation of population growth
What environmental factors stop a population from growing indefinitely?
Why do some populations show radical fluctuations in size over time, while others remain stable?
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30. Mechanisms of Density-Dependent Population Regulation
Density-dependent birth and death rates are an example of negative feedback that regulates population growth
Density-dependent birth and death rates are affected by many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors
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31. Density-Dependent Controls
Competition for resources
Predation
Parasitism
Disease

32. Competition for Resources
In crowded populations, increasing population density intensifies competition for resources and results in a lower birth rate
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33. Toxic Wastes
Accumulation of toxic wastes can contribute to density-dependent regulation of population size
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34. Predation
As a prey population builds up, predators may feed preferentially on that species
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35. Intrinsic Factors
For some populations, intrinsic (physiological) factors appear to regulate population size
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36. Territoriality
In many vertebrates and some invertebrates, competition for territory may limit density
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37. Disease
Population density can influence the health and survival of organisms
In dense populations, pathogens can spread more rapidly
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38. Figure 53.17f
Figure Exploring: Mechanisms of Density-Dependent Regulation 38

39. Density-Independent Controls
Natural disasters
Severe weather
Pollution
Pesticide spraying

40. Population Cycles: Scientific Inquiry
Some populations undergo regular boom-and-bust cycles
Lynx populations follow the 10-year boom-and-bust cycle of hare populations
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41. Number of hares (thousands) Number of lynx (thousands)
Figure 53.19
Snowshoe hare
160
120 80 40 9 6 3
Number of hares (thousands)
Lynx
Number of lynx (thousands)
Figure Population cycles in the snowshoe hare and lynx.
1850
1875
1900
1925
Year 41

42. Figure 53.18 50 40 30 20 10
2,500
2,000
1,500
1,000
500
Wolves
Moose
Number of wolves
Number of moose
Figure Fluctuations in moose and wolf populations on Isle Royale, 1959–2008.
1955
1965
1975
1985
1995
2005
Year 42

43. The Global Human Population
Figure 53.22
The Global Human Population 7 6 5 4 3 2 1
The human population increased relatively slowly until about 1650 and then began to grow exponentially
Human population (billions)
The Plague
Figure Human population growth (data as of 2009).
8000
BCE
4000
BCE
3000
BCE
2000
BCE
1000
BCE
1000 CE
2000 CE 43

44. The global population is more than 6.8 billion people
Though the global population is still growing, the rate of growth began to slow during the 1960s
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45. Annual percent increase
Figure 53.23
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
2009
Annual percent increase
Projected data
Figure Annual percent increase in the global human population (data as of 2009).
1950
1975
2000
2025
2050
Year 45

46. Regional Patterns of Population Change
To maintain population stability, a regional human population can exist in one of two configurations
Zero population growth = High birth rate – High death rate
Zero population growth = Low birth rate – Low death rate
The demographic transition is the move from the first state to the second state
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47. Rapid growth Afghanistan Slow growth United States No growth Italy
Figure 53.24
Rapid growth
Afghanistan
Slow growth
United States
No growth
Italy
Male
Female
Age
85+
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
Male
Female
Age
85+
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
Male
Female
Figure Age-structure pyramids for the human population of three countries (data as of 2009). 10 8 6 4 2 2 4 6 8 10 8 6 4 2 2 4 6 8 8 6 4 2 2 4 6 8
Percent of population
Percent of population
Percent of population 47

48. Age structure diagrams can predict a population’s growth trends
The demographic transition is associated with an increase in the quality of health care and improved access to education, especially for women
Most of the current global population growth is concentrated in developing countries
Age structure diagrams can predict a population’s growth trends
They can illuminate social conditions and help us plan for the future
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49. Infant Mortality and Life Expectancy
Infant mortality and life expectancy at birth vary greatly among developed and developing countries but do not capture the wide range of the human condition
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50. Infant mortality (deaths per 1,000 births)
Figure 53.25 60 50 40 30 20 10 80 60 40 20
Infant mortality (deaths per 1,000 births)
Life expectancy (years)
Figure Infant mortality and life expectancy at birth in industrialized and less industrialized countries (data as of 2008).
Indus- trialized countries
Less indus- trialized countries
Indus- trialized countries
Less indus- trialized countries 50

51. Global Carrying Capacity
How many humans can the biosphere support?
Population ecologists predict a global population of 7.810.8 billion people in 2050
The carrying capacity of Earth for humans is uncertain
The average estimate is 10–15 billion
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52. Limits on Human Population Size
The ecological footprint concept summarizes the aggregate land and water area needed to sustain the people of a nation
It is one measure of how close we are to the carrying capacity of Earth
Countries vary greatly in footprint size and available ecological capacity
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53. Figure 53.26 Annual per capita energy use around the world.
Gigajoules
> 300
150–300
50–150
10–50
< 10
Figure Annual per capita energy use around the world. 53

54. Population Ecology Chapter 35 Review Q’s
Questions prepared by
Eric Ribbens Western Illinois University
John Zarnetske Hoosick Falls Central Schools

55. Which of the following sets of measurements is the most useful when studying populations?
gene frequency over time and the ratio of reproductive to nonreproductive individuals
density, dispersion, and demographics of a population
minimum and minimum amounts of precipitation and annual temperature extremes
ratio of predators and the number of immigrants and emigrants
annual precipitation averages and mean annual temperatures
Answer: b

56. Population ecologists are primarily interested in
understanding how biotic and abiotic factors influence the density, distribution, size, and age structure of populations.
the overall vitality of a population of organisms.
how humans affect the size of wild populations of organisms.
studying interactions among populations of organisms that inhabit the same area.
how populations evolve as natural selection acts on heritable variations among individuals and changes in gene frequency.
Answer: a

57. A mark-recapture study would be a good way to find out how many
queens live in a beehive.
cubs that black bears in Minnesota are likely to have.
pine trees live in a forest.
fish live in a lake.
people speed on an interstate.
Answer: d

58. from Type I to Type II or III. from Type II to Type I.
Imagine that a species of fish used to be a broadcast spawner (producing many eggs that then get no subsequent parental care) but has evolved to be a mouth brooder (holding the eggs in the parent’s mouth until they hatch and then caring for the young for a while). We would expect the survivorship curve of this species to shift
from Type I to Type II or III.
from Type II to Type I.
from Type III to Type I or II.
from Type II to Type III.
The survivorship type would vary unpredictably.
Answer: c
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59. The exponential growth model describes the increase in population size of a population that is not constrained by resources or space. The graph shows the elephant population in Kruger National Park, which appears to have been reproducing exponentially from 1900 to From this graph, you can tell that
none of the elephants died.
a female elephant living around 1960 was more likely to have a baby than a female elephant living around 1920.
the elephants adapted to the new park conditions around 1955.
the vegetation the elephants eat could support more than 5,000 elephants.
the more elephants there are, the more tourists will visit the park.
Answer: d

60. a) Paramecium are a single-celled organism. b) Daphnia live in water.
The logistic model incorporates the idea of K, the carrying capacity, which is the maximum number of individuals the ecosystem can sustain over time. Essential to this idea is the concept that population growth rates are reduced when the population size approaches K. Look at the graphs on the next slide. Both Paramecium and Daphnia have population dynamics that stabilize around K. However, Daphnia overshot their carrying capacity, but Paramecium did not. This is probably because
a) Paramecium are a single-celled organism.
b) Daphnia live in water.
c) the Daphnia had to learn what their carrying capacity was.
d) the Paramecium population had a bigger K (about 800) than Daphnia (about 120).
e) something about Daphnia responds differently to K than Paramecium.
Answer: e

62. From the following graph you can tell that
families in Mexico are still more likely to be bigger than families in Sweden.
more people live in Mexico than in Sweden.
birth rates and death rates do not appear to be correlated.
a Swedish person born in 1900 is more likely to be dead than a Mexican person born in 1900.
these populations are probably far away from their carrying capacity.
Answer: a

63. The graph shows the percent increase in the global human population
The graph shows the percent increase in the global human population. There is a sharp dip around 1960, which the legend says is due mainly to a famine in China in which 60 million people died. The graph also predicts that the percent increase is dropping and will continue to drop throughout the 21st century. Which of the following statements is true?
The famine in China and the 21st-century decline are both examples of density-independent factors.
The famine in China and the 21st-century decline are both examples of density-dependent factors.
The famine in China was density-independent, but the 21st-century decline is density dependent.
The famine in China was density-dependent, but the 21st-century decline is density independent.
Because the causes of the famine and the 21st-century decline are different, you cannot tell whether they are density dependent.
Answer: b

64. Most ecologists agree that people should not be using more than 1
Most ecologists agree that people should not be using more than 1.7 ha of resources if they want to be sustainable. People in the United States use an average of 10 ha. This implies that
the ecological footprint concept is flawed.
the United States has more land than other countries do.
U.S. rates of resource consumption are too high.
U.S. people are happier.
U.S. people are less likely to emigrate.
Answer: c