Chapter 52
Population Ecology
I. Population Density, Dispersion
and Demography
Dynamic biological processes
– Birth rates/death rates;
immigration/emigration
– Patterns: Clumped, Uniform, Random
Demography
– Life tables
– Survivorship curves (figures 52.4 and 52.5)
– Reproductive rates
LE 52-2
Births
Immigration
Population
size
Emigration
Deaths
LE 52-3
Clumped. For many animals, such as these wolves,
living in groups increases the effectiveness of hunting,
spreads the work of protecting and caring for young,
and helps exclude other individuals from their territory.
Uniform. Birds nesting on small islands, such as these
king penguins on South Georgia Island in the South
Atlantic Ocean, often exhibit uniform spacing, maintained
by aggressive interactions between neighbors.
Random. Dandelions grow from windblown seeds that
land at random and later germinate.
II. Life History and Natural
Selection
Life history variables
– When reproduction begins, how often, how
many
Life history diversity
– Semelparity (Big bang reproduction)
– Iteroparity (Repeated reproduction
Trade offs
Number of survivors (log scale)
LE 52-5
1,000
I
100
II
10
III
1
0
50
Percentage of maximum life span
100
LE 52-8
Most weedy plants, such as this dandelion, grow quickly and
produce a large number of seeds, ensuring that at least some
will grow into plants and eventually produce seeds themselves.
Some plants, such as this coconut palm, produce a moderate
number of very large seeds. The large endosperm provides
nutrients for the embryo, an adaptation that helps ensure the
success of a relatively large fraction of offspring.
III. Exponential vs. Logistic Growth
Exponential
– Unlimited resources
Logistic
– Carrying capacity
LE 52-10
Elephant population
8,000
6,000
4,000
2,000
0
1900
1920
1940
Year
1960
1980
LE 52-12
2,000
Population size (N)
dN
= 1.0N
dt
Exponential
growth
1,500
K = 1,500
Logistic growth
1,000
dN
= 1.0N
dt
1,500 – N
1,500
500
0
0
5
10
Number of generations
15
Number of Daphnia/50 mL
LE 52-13b
180
150
120
90
60
30
0
0
20
40
60 80 100 120 140 160
Time (days)
A Daphnia population in the lab
LE 52-13c
Number of females
80
60
40
20
0
1975
1980 1985 1990 1995 2000
Time (years)
A song sparrow population in its natural habitat
IV. Regulation of Populations
Density-dependent and densityindependent
Dynamics of population growth -> variation
Population cycles
LE 52-18
Moose population size
2,500
Steady decline probably
caused largely by wolf
predation
2,000
1,500
1,000
Dramatic collapse caused by severe
winter weather and food shortage,
leading to starvation of more than
75% of the population
500
0
1960
1970
1980
Year
1990
2000
LE 52-19
Commercial catch (kg) of
male crabs (log scale)
730,000
100,000
10,000
1950
1960
1970
Year
1980
1990
Hare population size
(thousands)
160
120
Lynx
80
6
40
3
0
0
1850
1875
1900
Year
9
1925
Lynx population size
(thousands)
LE 52-21
Snowshoe hare
V. Human Population
Figure 52.23
Regional
– Demographic transition
– Age structure
Global Carrying Capacity
6
5
4
3
2
The Plague
1
8000
B.C.
4000
B.C.
3000
B.C.
2000
B.C.
1000
B.C.
0
1000
A.D.
0
2000
A.D.
Human population (billions)
LE 52-22
6
5
4
3
2
The Plague
1
8000
B.C.
4000
B.C.
3000
B.C.
2000
B.C.
1000
B.C.
0
1000
A.D.
0
2000
A.D.
Human population (billions)
LE 52-22
LE 52-25
Rapid growth
Afghanistan
Male
Female
Slow growth
United States
Male
Female
Age
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
8
6
4
2
0
2
4
6
Percent of population
8
Decrease
Italy
Male
Female
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
8
6
4
2
0
2
4
6
Percent of population
8
8
6
4
2
0
2
4
6
Percent of population
8
LE 52-26
80
50
Life expectancy (years)
Infant mortality (deaths per 1,000 births)
60
40
30
20
60
40
20
10
0
0
Developed
countries
Developing
countries
Developed
countries
Developing
countries