Chapter 52: Population Ecology
1. What is a population?
- Individuals of a single species that occupy the same general area
2. What is the difference between density & dispersion?
- Density – number of individuals per unit area or volume
- Dispersion – pattern of spacing within the boundaries of population
Figure 52.2 Population dynamics
Factors that influence density…..
Births and immigration add
individuals to a population.
Births
Immigration
Increase
PopuIation
size
Emigration
Deaths
Deaths and emigration
remove individuals from
a population.
Decrease
Fig. 52.3 Patterns of dispersion within a population’s geographic
range
(a) 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.
(b) 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.
(c) Random. Dandelions
grow from windblown
seeds that land at
random and later
germinate.
Chapter 52: Population Ecology
1. What is a population?
- Individuals of a single species that occupy the same general area
2. What is the difference between density & dispersion?
- Density – number of individuals per unit area or volume
- Dispersion – pattern of spacing within the boundaries of population
3. What factors influence population size?
- Birth rate – fecundity
- Death rate
- Generation time
- Sex ratio
4. What do the survivorship curves mean?
Figure 52.5 Idealized survivorship curves: Types I, II, and III
1,000
Number of survivors (log scale)
I
100
II
10
III
1
0
50
100
Percentage of maximum life span
Type I – most born survive & live to their maximum life span – us – k-selected
Type II – constant death rate – each day has an equal opportunity for life or death
Type III – high early death rate but survivors live to maximum life span – r-selected
Chapter 52: Population Ecology
1.
2.
3.
4.
5.
What is a population?
What is the difference between density & dispersion?
What factors influence population size?
What do the survivorship curves mean?
What are the 2 main populations growth curves?
- Exponential – “J”-curve
Figure 52.9 Population growth predicted by the exponential model
2,000
dN = Δ population size
dt = Δ time
rmax = Births – deaths
(intrinsic rate of increase)
N = population size
Population size (N)
dN
 1.0N
dt
1,500
dN
 0.5N
dt
1,000
500
0
0
5
10
15
Number of generations
Species whose population size is primarily determined by birth rate = r-selected species
Self-Quiz
• A uniform dispersion pattern for a
population may indicate that
– A. the population is spreading out and
increasing its range.
– B. resources are heterogeneously distributed.
– C. individuals of the population are competing
for some resource, such as water and
minerals for plants or nesting sites for
animals.
– D. there is an absence of strong attractions or
repulsions among individuals.
Self-Quiz
• I would expect the potential for social
interactions among individuals to be
maximized when individuals
– A. are randomly distributed in their
environment.
– B. are uniformly distributed in their
environment.
– C. have a clumped distribution in their
environment.
– D. are non-randomly distributed in their
environment.
Self-Quiz
• Humans are an example of an organism
with a type I survivorship curve. This
means
– A. mortality rates are highest for younger
individuals.
– B. mortality rates are highest for older
individuals.
– C. mortality rates are constant over the life
span of individuals.
– D. the population growth rate is high.
Ticket Out the Door
Chapter 52: Population Ecology
1.
2.
3.
4.
5.
What is a population?
What is the difference between density & dispersion?
What factors influence population size?
What do the survivorship curves mean?
What are the 2 main populations growth curves?
- Exponential
- Logistic
Figure 52.12 Population growth predicted by the logistic model
2,000
Population size (N)
dN
 1.0N
dt
1,500
Exponential
growth
K = carrying capacity
K  1,500
Logistic growth
1,000
dN
 1.0N
dt
1,500  N
1,500
500
0
0
5
10
15
Number of generations
Species whose population size is primarily determined by carrying capacity
= k-selected species
Chapter 52: Population Ecology
1.
2.
3.
4.
5.
6.
What is a population?
What is the difference between density & dispersion?
What factors influence population size?
What do the survivorship curves mean?
What are the 2 main populations growth curves?
What is the difference between r-selected & k-selected species?
r-selected (generalists) k-selected (equilibrial)
Maturation time:
short
long
Lifespan:
short
long
Death rate
high
low
Offspring/episode:
many
few
Size of offspring/eggs:
small
large
Parental care:
none
extensive
Timing of 1st reproduction: early
late in life
Reproductions/lifetime:
usually 1
several
Examples:
insects, fish, frogs
mammals, birds
7. What factors limit a population?
Chapter 52: Population Ecology
1.
2.
3.
4.
5.
6.
7.
What is a population?
What is the difference between density & dispersion?
What factors influence population size?
What do the survivorship curves mean?
What are the 2 main populations growth curves?
What is the difference between r-selected & k-selected species?
What factors limit a population?
- Density – dependent factors – intensify as population size increases
- Resource limitation
- Health
- Predation
- Waste accumulation
- Density – independent factors – effect population regardless of density
- Weather
- Climate
- Environmental disasters
160
Snowshoe hare
120
Lynx
9
80
6
40
3
0
0
1850
1875
1900
Year
1925
Lynx population size
(thousands)
Hare population size
(thousands)
Figure 52.21 Population cycles in the snowshoe hare and lynx
Chapter 52: Population Ecology
1.
2.
3.
4.
5.
6.
7.
8.
What is a population?
What is the difference between density & dispersion?
What factors influence population size?
What do the survivorship curves mean?
What are the 2 main populations growth curves?
What is the difference between r-selected & k-selected species?
What factors limit a population?
How has the human population changed & how is it shown?
Figure 52.22 Human population growth (data as of 2003)
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)
6
Figure 52.25 Age-structure pyramids for the human population of
three countries (data as of 2003)
Rapid growth
Afghanistan
Male
Female
8 6 4 2 0 2 4 6 8
Percent of population
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
Slow growth
United States
Female
Male
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 8
Percent of population
Wide base = rapid growth Same width = slow growth
Decrease
Italy
Female
Male
Group
NOT
making
babies
Group
making
babies
Babies
8 6 4 2 0 2 4 6 8
Percent of population
Narrow base = decreasing
Self-Quiz
• A population’s carrying capacity is
– A. the number of individuals in that
population.
– B. a constant that can be estimated for all
populations.
– C. inversely related to r.
– D. The population size that can be supported
by available resources for that species within
the habitat.