Population Ecology

1
Population Ecology
Chapter 52
2
Population a group of individuals of a single
species that simultaneously occupy the same
general area
Static population pattern property of a
population that can be assessed with a
measurement or estimate at a single point in time
(a snapshot)
Dynamic population pattern property of a
population that can only be assessed with
measurements or estimates taken at two or more
points in time
3
Static population patterns
Geographic range a populations global
distribution
Fig. 50.2
4
Static population patterns
Population size the total number of individuals
in a population
Fig. 50.2
5
Static population patterns
Density the number of individuals per area
Fig. 50.2
6
Static population patterns
Dispersion the pattern of spacing among
individuals
This map is NOT informative about dispersion!
Fig. 50.2
7
Static population patterns
Dispersion the pattern of spacing among
individuals
Random nearest neighbors are as near as
predicted if all individuals were randomly placed
within the focal boundaries
Fig. 52.3c
8
Static population patterns
Dispersion the pattern of spacing among
individuals
Clumped (a.k.a. aggregated) nearest neighbors
are nearer, on average, than a random dispersion
pattern would predict
Fig. 52.3a
9
Static population patterns
Dispersion the pattern of spacing among
individuals
Uniform (a.k.a. regular) nearest neighbors are
farther away, on average, than a random
dispersion pattern would predict
Fig. 52.3b
10
Dynamic population patterns
Geographic range, population size, density,
dispersion can all change through time
Fig. 52.19
11
Dynamic population patterns
Consider population size a population can grow,
decline, or otherwise fluctuate
Fig. 52.19
12
Demography
The study of vital statistics that affect
population size
Fig. 52.19
13
Demography
Life table an age-specific summary of survival
Table 52.1
14
Demography
Life tables are often constructed by following
the fate of a cohort
Table 52.1
15
Demography
Cohort a group of individuals of the same age
(or stage)
Table 52.1
16
Demography
Survivorship curve a plot of the proportion out
of a cohort alive at each age
Figure 52.5
17
Demography
Survivorship curve a plot of the proportion out
of a cohort alive at each age
18
Demography
Reproductive table (a.k.a., fertility schedule)
age-specific reproductive rates
Table 52.2
19
Demography
Age structure the relative number of
individuals of each age in a population
Figure 52.25
20
Demography
Age structure the relative number of
individuals of each age in a population
21
Demography
Age structure the relative number of
individuals of each age in a population
22
Demography
Each population has its own characteristic vital
rates (demographic parameters)
The values of vital rates depend on the traits of
the focal organisms
23
For example
Coconut palms and kiwis produce a few, big
offspring with high survivorship probabilities
24
For example
Dandelions and salmon produce many, tiny
offspring with low survivorship probabilities
25
The traits that affect an organisms vital rates,
as well as the values of the vital rates
themselves, comprise an organisms life history
vs.
26
Fitness costs and benefits shape life-history
strategies
vs.
27
Fitness costs and benefits are often balanced
around life-history trade-offs
Trait Y
E.g., Seed size
Trait X
E.g., Seed number
28
Fitness costs and benefits are often balanced
around life-history trade-offs
Trait Y
E.g., Number of lifetime reproductive episodes
Iteroparity
Semelparity (A single reproductive bout per
lifetime)
Trait X
E.g., Number of offspring per reproductive
episode
29
Fitness costs and benefits are often balanced
around life-history trade-offs
Current year reproduction vs. subsequent survival
Fig. 52.7
30
Changes in population size (N)
The following four processes can change the size
of a population
1. Birth
2. Death
3. Immigration
4. Emigration
Fig. 52.2
31
Changes in population size (N)
In a population closed to immigration and
emigration
N
B - D
t
N
the change in N for a given change in time

t
B the number of births
D the number of deaths
32
Changes in population size (N)
We can also write the equation in terms of per
capita birth and death rates
N
bN - dN
t
N
the change in N for a given change in time

t
b the per capita birth rate
d the per capita death rate
33
Changes in population size (N)
We can substitute r (b - d) to give
N
rN
t
r per capita growth rate
If r gt 0, population grows
If r lt 0, population declines
If r 0, population size remains the
same
34
Changes in population size (N)
We can substitute r (b - d) to give
N
rN
t
For example
N21500
N11000
rN500 r0.5
35
Changes in population size (N)
A population with unlimited resources would
achieve its maximum growth rate
N
rmaxN
t
This is known as exponential growth
36
Changes in population size (N)
Exponential growth is unlimited
Fig. 52.12
37
Changes in population size (N)
An example of exponential growth
38
Changes in population size (N)
An example of near-exponential growth
39
Changes in population size (N)
An example of near-exponential growth
40
Changes in population size (N)
Real-world populations never continue growing
exponentially indefinitely
Fig. 52.12
41
Changes in population size (N)
Because many factors limit maximum population
sizes, especially resources
Fig. 52.12
42
Changes in population size (N)
Carrying capacity (K) is the ceiling population
size set by limited resources
Fig. 52.12
43
Changes in population size (N)
Logistic population growth describes a population
that grows to carrying capacity
Fig. 52.12
44
Changes in population size (N)
An example of logistic growth
45
Changes in population size (N)
An example of near-logistic growth
46
Changes in population size (N)
An example of near-logistic growth
Fig. 52.13b
47
Changes in population size (N)
The logistic equation incorporates a term that
slows population change near K
N
rmaxN (K - N / K)
t
Fig. 52.11
48
Changes in population size (N)
Density-dependent population change will tend to
stabilize population size
N
rmaxN (K - N / K)
t
Fig. 52.11
49
Changes in population size
Density-dependent population change requires at
least one density-dependent vital rate
Fig. 52.14
50
Changes in population size (N)
Density-dependent population change requires at
least one density-dependent vital rate
Fig.52.15
51
Changes in population size (N)
Fluctuations in population size are common in
nature
Fig. 52.13c
52
Changes in population size (N)
Some populations follow boom-and-bust cycles
Fig. 52.21
53
Changes in population size (N)
Global human population trends are frightening
Fig. 52.22
54
Changes in population size (N)
How long do we have until disaster strikes?
16
14
12
New Zealand
10
USA
Germany
Australia
8
Ecological footprint (ha per person)
Netherlands
Japan
Canada
Norway
6
Sweden
UK
4
Spain
World
2
China
India
0
2
4
6
8
10
12
14
16
0
Available ecological capacity (ha per person)
Fig. 52.27