Population Growth

1
Population Growth

• Exponential growth
• No population can continue to grow indefinitely.
• At high densities, growth becomes
  density-dependent. (Fig. 48.3)
• All populations eventually reach the carrying
  capacity of their habitat. (the max number that
  can be supported by available resources).

2
Figure 48.3
Carrying capacity
Population size
Time
3
Case Studies Explaining How Population Size
Changes Over Time

• Humans exhibiting density-dependent growth (Fig.
  48.5a,b)

4
Figure 48.5a
Historical growth
6
1999 6 billion
1900 1.5 billion
5
1700 600 million
4
1500 400 million
Human population (billions)
3
1 A.D. 150200 million
2
45 million
1
0
10,000 B.C.
8000
6000
4000
2000
0
2000 A.D.
Year
5
Figure 48.5b
Recent growth
12
11
10
High
1998 Projections
9
Medium
8
Low
7
Human population size (billions)
6
5
4
3
2
1950
1970
1990
2010
2030
2050
Year
6
Figure 48.5c
1992 Projections
Projected population in 2050
Fertility rate
12.5 billion
High
Medium
10.15 billion
Low
7.8 billion
The 1992 projections for 2050 are higher than
those from 1998 primarily because the earlier
projections did not account for the impact of
AIDS.
7
Population Structure

• Age structure
• Developed nations have an age distribution that
  tends to be even. (Fig. 48.9a)
• Developing nations have an age distribution that
  is bottom-heavy (mostly young individuals).
  (Fig. 48.9b)

8
Figure 48.9a
More-developed countries
100
1998 data
95
90
85
2050 projections
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
0
20
20
40
40
60
60
(In millions)
Females
Males
9
Figure 48.9b
Less-developed countries
100
95
1998 data
90
85
2050 projections
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
0
100
100
200
200
300
300
(in millions)
Females
Males
10
Population Structure

• Geographic structure
• Many species exist as a metapopulation.
• Small, isolated populations, even those on nature
  reserves, are unlikely to survive over the long
  term. (Fig. 48.10a-c)

11
Figure 48.10a
A metapopulation is made up of small, isolated
populations.
Individuals
Habitat patches
12
Figure 48.10b
Although some subpopulations go extinct over
time...
13
Figure 48.10c
migration can restore or establish
subpopulations.
14
Figure 48.11
15
Demography and Conservation

• Demography the study of factors that determine
  the size and structure of populations through
  time.

16
Demography and Conservation

• Life tables
• Summarize the probability that an individual will
  survive and reproduce in any given year over the
  course of its lifetime. (Fig. 48.13a)
• Survivorship - Ix Nx / N0
• Fecundity the number of female offspring
  produced by each female in a population.

17
Figure 48.13a
Three general types of survivorship curves
1000
Type l
High survivorship
100
Type ll
Low survivorship
Number of survivors (Nx)
Low survivorship
Steady survivorship
10
1
Type lll
High survivorship
0.1
Age
18
Demography and Conservation

• Life tables
• Contain useful pieces of information, such as
  survivorship, fecundity, and net reproductive
  rate.

19
Figure 48.14a
Life table
Age (x)
Survivorship (lx)
Fecundity (mx)
0 (birth)
0.0
3.0
0.33
1
2
4.0
0.2
0.2
5.0
3
20
Demography and Conservation

• Life tables
• Can be used to make population projections and
  guide conservation programs.

21
Demography and Conservation

• Population viability analysis (PVA)
• A model that estimates the likelihood that a
  population will avoid extinction for a given
  time period.
• Combine demographic models with geographic
  structure and rate and severity of habitat
  disturbance.

22
Demography and Conservation

• Population viability analysis (PVA)
• Populations are considered viable if they have a
  95 probability of surviving for at least 100
  years.

23
Demography and Conservation

• Population viability analysis (PVA)
• Currently being used by natural resource
  managers. (Fig. 48.15a,b)

24
Box 48.1, Figure 1