1. Chapter 26 – Population growth & regulation
World population clock

2. Chapter 26 – Population Growth & Regulation
What is a population?
What causes population size changes?
How is the human population changing?
What are the environmental effects of population changes?

3. What is a population?
All members of a species that live within an ecosystem and can potentially interbreed

4. Population growth A. Factors influencing population growth (p. 514)
1. Birthrate
2. Death rate
3. Migration
a. Immigration
b. Emigration

5. Population growth
B. Biotic potential—maximal growth rate given ideal conditions (p. 514)
Produces exponential growth if not restrained

6. bacteria Exponential growth curves are J-shaped. time (minutes)
number of
bacteria
bacteria
Exponential
growth curves
are J-shaped.
number of individuals
FIGURE 26-1a (part 2) Exponential growth curves are J-shaped
All such curves share a similar J shape; the major difference is the time scale. (a) Growth of a population of bacteria, starting with a single individual and with a doubling time of 20 minutes.
time (minutes)
Figure 26-1a (part 2) Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

7. number of cranes
FIGURE 26-5 Exponential growth of wild whooping cranes
Hunting and habitat destruction had reduced the world's whooping crane population to about 20 before they were protected in By 2005, their wild population had grown to 340 individuals. Notice the J-curve characteristic of exponential growth.
year
Figure Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

8. Death rate influences population growth
bacteria No
deaths.
10% die
between
doublings.
number of individuals
25% die
between
doublings.
FIGURE 26-2 The effect of death rates on population growth
The graphs assume that a bacterial population doubles every 20 minutes. Notice that the population in which a quarter of the bacteria die every 20 minutes reaches 2500 only 2 hours and 20 minutes later than one in which no deaths occur.
time (hours)
Figure Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

9. Invasive (exotic) species often show exponential growth (p. 518)
Left: nutria; Right: kudzu

10. Population growth
C. Environmental resistance limits population growth (p. 518)
1. Decreases birthrate, increases death rate
2. Density-dependent factors
a. Predation
b. Parasitism, disease
Competition (inter- and intraspecific)
Food & space

11. Human activity can influence population growth
Clark
Lewis

12. How do you reconcile a belief in a loving God who apparently designed cats to enjoy the slow painful death of their prey?

13. I. Population growth C. Environmental resistance (cont.)
3. Density-independent factors (p. 522)
a. Climate & weather
b. Pesticides & pollutants

14. population stabilizes around carrying capacity. number of individuals
A logistic growth curve (S-curve) stabilizes at K (carrying capacity, p. 518). K
Growth
rate slows.
Growth stops and
population stabilizes
around carrying capacity.
number of individuals
Population
grows rapidly.
FIGURE 26-6a The S-curve of logistic population growth
(a) During logistic growth, the population will remain small for a time, then will expand increasingly rapidly for a time. Then the growth rate slows and growth eventually ceases at or near the carrying capacity (K). The result is a curve shaped like a "lazy s."
time
Figure 26-6a Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

15. (NIYB) Figure: 38.5 Title: The S-curve of population growth Caption:
The population grows exponentially at first, then fluctuates around the carrying capacity. The growth is driven by biotic potential but levels off owing to environmental resistance.

16. Consequences of exceeding K.
Population
overshoots
carrying
capacity;
environment
is damaged. K
(original)
Low damage;
resources recover,
population fluctuates. K
(reduced)
Extreme
damage;
population
dies out.
FIGURE 26-6b The S-curve of logistic population growth
(b) In nature, populations can overshoot carrying capacity (K), but only for a limited time. Three possible results are illustrated.
High damage;
carrying capacity
permanently lowered.
time
Figure 26-6b Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

17. Boom-and-bust population cycle (p. 517)
Nutrients are depleted.
Favorable growth
conditions occur.
population density
“boom”
“bust”
FIGURE 26-3 A boom-and-bust population cycle
Population density of cyanobacteria (blue-green algae) in an annual boom-and-bust cycle in a lake. Algae survive at a low level through the fall, winter, and spring. Early in July, conditions become favorable for growth, and exponential growth occurs through August. Nutrients soon become depleted, and the population "goes bust."
Jan
Mar
May
Jul
Sep
Nov
month
Figure Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

18. approximate number of lemmings per acre
FIGURE 26-4 Lemming population cycles follow a boom-and-bust pattern
Lemming population density follows roughly a four-year cycle (data from Point Barrow, Alaska).
1950
1955
1960
1965
year
Figure Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

19. Populations exhibit different spatial distributions (p. 524)
Clumped
Herds, flocks, schools
Predators and prey
Uniform
Territorial species
Random
Mostly plants

20. clumped
FIGURE 26-13a Population distributions
(a) Clumped: a gathering of caterpillars.
Figure 26-13a Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

21. uniform
FIGURE 26-13b Population distributions
(b) Uniform: creosote bushes in the desert.
Figure 26-13b Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

22. random
FIGURE 26-13c Population distributions
(c) Random: trees and other plants in a rain forest.
Figure 26-13c Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

23. Populations exhibit differences in survivorship (p. 525)
Early-loss
Large numbers of offspring
Constant-loss
Equal chance of dying at all ages
Some birds
Late-loss
Few offspring
Large and long-lived animals

24. (in percentage of maximum life span)
number of survivors
late loss
(human)
constant loss
(American robin)
FIGURE 26-14b Life tables and survivorship curves
(b) Three types of survivorship curve are shown. Because the life spans differ, the percentages of survivors (rather than ages) are used. (Source: National Vital Statistics Reports, Vol. 53, No. 6, November 10, 2004)
early loss
(dandelion)
age
(in percentage of maximum life span)
Figure 26-14b Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

25. Which of the following concerning populations is true?
A population consists of all the species that interact within a defined ecosystem
Populations always exhibit exponential growth
A population consists of all members of an interbreeding species in a defined area
Both 1 and 2
Both 2 and 3

26. Which of the following serves as a form of density-independent environmental resistance?
Availability of food
Infectious disease
A drought
All of these
None of these

27. Population effects of introduced species
Brown tree snake

28. Brown tree snakes
Will the brown tree snake population continue to show positive growth?

29. Human population growth
2012*
2006
Date
Billions
Time to add
each billion
(years)
1999
1804 1
All of human
history
1987
1927 2
123
1960 3 33
1975
1974 4 14
billions of people
1987 5 13
1999 6 12
bubonic plague
1960
2012 7* 13
1930
*projected
1830
FIGURE Human population growth
The human population from the Stone Age to the present has shown continued exponential growth as various advances overcame environmental resistance. Note the dip in the fourteenth century caused by the bubonic plague. Note also the time intervals over which additional billions were added. (Inset) Earth is an island of life in a sea of emptiness; its space and resources are limited.
Technical and
cultural advances
Agricultural advances
Industrial and
medical
advances
Figure Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

30. Genesis 9:7 As for you, be fruitful and increase in number; multiply on the earth and increase upon it.

31. Is the human population in a boom and bust cycle?
Figure: 38.6
Title:
The effects of exceeding carrying capacity
Caption:
Exceeding carrying capacity can damage an ecosystem, reducing its ability to support the population. In 1911, 25 reindeer were introduced onto one of the Pribilof Islands (St. Paul) in the Bering Sea off Alaska. Food was plentiful, and the reindeer encountered no predators on the island. The herd grew exponentially (note the initial J shape) until it reached 2000 reindeer in At this point, the small island was seriously overgrazed, food was scarce, and the population declined dramatically. By 1950, only eight reindeer survived.

32. Human population (p. 526) Why is it showing exponential growth?
How long will it remain exponential?
What is the carrying capacity for humans?

33. Human population growth – why growing so fast?
D. Our species continues to overcome environmental resistances
1. Medical advances, agricultural revolution

34. population (billions)
developing countries
FIGURE Mid-level UN population projections
developed countries
year
Figure Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

35. natural increase per year (percent)
World average: 1.2%
Developing countries average: 1.4%
Africa: 2.2%
Latin America/Caribbean: 1.6%
World regions
Asia (excluding China): 1.6%
China: 0.6%
Developed countries average: 0.3%
FIGURE Population change by world regions
Growth rates shown are due to natural increase (births - deaths) expressed as the percentage increase per year for various regions of the world. These figures do not include immigration or emigration. (Source: Data from the Population Reference Bureau, World Population Data Sheet, 2005; Eng.pdf).
N. America: 0.6%
Europe: –0.1%
natural increase per year (percent)
Figure Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

36. Age-structure diagrams predict future growth (p. 529-530)
Figure: 38.UN11b
Title:
Generalized age-structure diagrams
Caption:
The width of each figure is proportional to the number of individuals. The vertical axis shows increasing age.
RLF (p. 528) typically leads to stable population size

37. Age-structure diagrams online
(a) Developed countries
2006
2025
2050
75 and older
male
female
postreproductive (45–79 yr)
age
reproductive (15–44 yr)
0 - 14
prereproductive (0–14 yr)
millions of people
(b) Developing countries
75 and older
male
female
FIGURE Age structures of developed and developing countries
Notice that the predicted excess number of children over parents in developing countries is smaller in 2025 and in 2050, as these populations approach RLF. But as huge numbers of young people enter childbearing years, growth will continue. (Source: Data provided by the U.S. Census Bureau;
age
0 - 14
millions of people
Age-structure diagrams online
Figure Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

38. Population < 15 (%)
Source: Environmental Systems Research Institute

39. Infant mortality
Source: Environmental Systems Research Institute

40. Population growth rate (%)
Source: Environmental Systems Research Institute

41. Human population United States population U.S. pop. clock
-Fastest growing of all developed countries
-Fertility rate of 2.0
-Immigrant fertility rate >RLF
U.S. pop. clock
U.S. population (in millions)
year
Figure Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

42. U.S. population growth – is it a problem?
U.S. citizen uses 6x more energy than world average
<5% of population, but
-consumes 25% of energy
-22% of carbon dioxide & CFC emissions
Avg. of 3600 cal/day vs. world avg. of 2700 cal/day
Ecological footprint (p. 528 &533) 24ac pp, compared to 5.4ac pp worldwide

43. Has the human population exceeded its carrying capacity? (p. 528)
Estimated available 4.5ac per person
Current ecological footprint = 5.4 ac

44. U.S. population growth
By 2050 (Union of Concerned Scientists prediction):
crop/pasture land reduced in half
food prices 3-5x higher
30-50% of income spent on food (vs. 12%)
Sources:

45. U.S. population growth control?

46. Controlling population growth

47. How might a Christian respond to human population growth?
Are we abusing God’s creation?
Do other species, as God’s creation, have a right to space and natural resources?
What about birth control?
What about those in need?

48. 1 John 3:17-18 (NIV)
17 If anyone has material possessions and sees his brother in need but has no pity on him, how can the love of God be in him?
18 Dear children, let us not love with words or tongue but with actions and in truth.

49. This figure is the age-structure diagram of ___________ population.
An expanding
A stable
A shrinking
Question 26-21
Answer: 1
Diff: Moderate
Text Ref: 26.3
Skill: Conceptual
Notes:
This question can help students interpret age-structure diagrams. You can use it to introduce the characteristics of each type of age structure.

50. Which of the following concerning the human population is true?
The United States has the fastest growing human population in the world
Developing countries have a slower growth rate than developed countries
The human population is growing exponentially
All of these
None of these