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Population Ecology. Chapter 52. 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”).

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Population ecology
Population Ecology

Chapter 52


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


Static population patterns

Geographic range – a population’s global distribution

Fig. 50.2


Static population patterns

Population size – the total number of individuals in a population

Fig. 50.2


Static population patterns

Density – the number of individuals per area

Fig. 50.2


Static population patterns

Dispersion – the pattern of spacing among individuals

This map is NOT informative about dispersion!

Fig. 50.2


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


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


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


Dynamic population patterns

Geographic range, population size, density, dispersion can all change through time

Fig. 52.19


Dynamic population patterns

Consider population size; a population can grow, decline, or otherwise fluctuate

Fig. 52.19


Demography

The study of vital statistics that affect population size

Fig. 52.19


Demography

Life table – an age-specific summary of survival

Table 52.1


Demography

Life tables are often constructed by following the fate of a cohort

Table 52.1


Demography

Cohort – a group of individuals of the same age (or stage)

Table 52.1


Demography

Survivorship curve – a plot of the proportion out of a cohort alive at each age

Figure 52.5


Demography

Survivorship curve – a plot of the proportion out of a cohort alive at each age


Demography

Reproductive table(a.k.a., fertility schedule) – age-specific reproductive rates

Table 52.2


Demography

Age structure – the relative number of individuals of each age in a population

Figure 52.25


Demography

Age structure – the relative number of individuals of each age in a population


Demography

Age structure – the relative number of individuals of each age in a population


Demography

Each population has its own characteristic vital rates(demographic parameters)

The values of vital rates depend on the traits of the focal organisms…


For example…

Coconut palms and kiwis produce a few, big offspring with high survivorship probabilities


For example…

Dandelions and salmon produce many, tiny offspring with low survivorship probabilities


The traits that affect an organism’s vital rates, as well as the values of the vital rates themselves, comprise an organism’s life history

vs.


Fitness costs and benefits shape as the values of the vital rates themselves, comprise an organism’s life-history strategies

vs.


Fitness costs and benefits are often balanced around as the values of the vital rates themselves, comprise an organism’s life-history trade-offs

Trait Y

E.g.,

Seed size

Trait X

E.g., Seed number


Fitness costs and benefits are often balanced around as the values of the vital rates themselves, comprise an organism’s 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


Fitness costs and benefits are often balanced around as the values of the vital rates themselves, comprise an organism’s life-history trade-offs

Current year reproduction vs. subsequent survival

Fig. 52.7


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

The following four processes can change the size of a population:

1. Birth

2. Death

3. Immigration

4. Emigration

Fig. 52.2


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

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


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

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


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

We can substitute r = (b - d) to give:

N

= rN

t

r = per capita growth rate

If r > 0, population grows

If r < 0, population declines

If r = 0, population size

remains the same


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

We can substitute r = (b - d) to give:

N

= rN

t

For example…

N2=1500

N1=1000

rN=500; r=0.5


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

A population with unlimited resources would achieve its maximum growth rate:

N

= rmaxN

t

This is known as exponential growth


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

Exponential growth is unlimited…

Fig. 52.12


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

An example of exponential growth:


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

An example of near-exponential growth:


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

An example of near-exponential growth:


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

Real-world populations never continue growing exponentially indefinitely…

Fig. 52.12


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

Because many factors limit maximum population sizes, especially resources

Fig. 52.12


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

Carrying capacity (K) is the ceiling population size set by limited resources

Fig. 52.12


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

Logistic population growth describes a population that grows to carrying capacity

Fig. 52.12


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

An example of logistic growth:


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

An example of near-logistic growth:


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

An example of near-logistic growth:

Fig. 52.13b


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

The logistic equation incorporates a term that slows population change near K:

N

= rmaxN (K - N / K)

t

Fig. 52.11


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

Density-dependent population change will tend to stabilize population size

N

= rmaxN (K - N / K)

t

Fig. 52.11


Changes in population size as the values of the vital rates themselves, comprise an organism’s

Density-dependent population change requires at least one density-dependent vital rate

Fig. 52.14


4.0 as the values of the vital rates themselves, comprise an organism’s

10,000

3.8

3.6

Average number of seeds per reproducing individual (log scale)

1,000

3.4

Average clutch size

3.2

3.0

100

2.8

0

0

40

50

60

80

20

30

10

70

0

10

100

Seeds planted per m2

Density of females

Changes in population size (N)

Density-dependent population change requires at least one density-dependent vital rate

Fig.52.15


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

Fluctuations in population size are common in nature

Fig. 52.13c


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

Some populations follow boom-and-bust cycles

Fig. 52.21


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

Global human population trends are frightening

Fig. 52.22


Changes in population size (N) as the values of the vital rates themselves, comprise an organism’s

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

16

4

2

6

8

10

12

14

0

Available ecological capacity (ha per person)

Fig. 52.27


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