Populations

43

Chapter 43 Populations

Key Concepts• 43.1 Populations Are Patchy in Space and Dynamic

over Time• 43.2 Births Increase and Deaths Decrease

Population Size• 43.3 Life Histories Determine Population Growth

Rates• 43.4 Populations Grow Multiplicatively, but Not for

Long

Chapter 43 Populations

Key Concepts• 43.5 Extinction and Recolonization Affect

Population Dynamics• 43.6 Ecology Provides Tools for Managing

Populations

Chapter 43 Opening Question

How does understanding the population ecology of disease vectors help us combat infectious diseases?

Chapter 43 Opener

Desert landscapes tend to be a mosaic of patches of vegetation and areas of bare soil. In the Monte Desert of Argentina, seed production by grass is triggered by spring and summer rainfall. The number of seeds produced by each individual plant of the grass species Aristida mendocina increases with the amount of rainfall that occurs during summer months. Some summers are wetter than others, due to natural variation in climate.

Suppose you measure the population density of this grass in a study plot before a particularly wet summer, and again some time after the summer (enough time for seeds to be shed and wind-dispersed away from the parent to germinate).

Discuss what you would expect to see.

Concept 43.1 Populations Are Patchy in Space and Dynamic over Time

What will happen to the population density?

a. It will stay the same because nature is “in balance” and populations always remain stable.

b. It will increase within the study plot only.

c. It will increase within the study plot, and areas outside the plot that were formerly bare soil may also be colonized by grasses.

d. It will decline both inside and outside the plot.

e. None of the above

Concept 43.1 Populations Are Patchy in Space and Dynamic over Time

Figure 43.1 Species Are Patchily Distributed on Several Spatial Scales

Figure 43.1 Species Are Patchily Distributed on Several Spatial Scales (Part 1)

Figure 43.1 Species Are Patchily Distributed on Several Spatial Scales (Part 2)

Figure 43.2 Population Densities Are Dynamic and Interconnected

Consider the validity of the following statement:

Birth and death data from one individual within a population can be extrapolated to provide birth rates and death rates for the entire population.

Concept 43.2 Births Increase and Deaths Decrease Population Size

Can birth and death data from one individual within a population be extrapolated to provide birth rates and death rates for the entire population?

a. Yes, if the individual is young.

b. Yes, if the individual is old.

c. No, because there is individual variation in birth rates, so we have to calculate an average birth rate from a representative sample of individuals and use that to calculate per capita birth rates.

d. No, because there is individual variation in death rates, so we have to calculate the average individual chance of dying from a representative sample of individuals and use that to calculate per capita death rates.

e. Both c and d

Concept 43.2 Births Increase and Deaths Decrease Population Size

Which of the following factors can be used to explain a decline in the size of a population through time?

• Per capita birth rates b have decreased

• Per capita death rates d have decreased

• Per capita death rates d have increased

Concept 43.2 Births Increase and Deaths Decrease Population Size

Which of the following factors can explain a decline in the size of a population through time?

a. Per capita birth rates b have decreased

b. Per capita death rates d have decreased

c. Per capita death rates d have increased

d. Both a and c

e. None of the above

Concept 43.2 Births Increase and Deaths Decrease Population Size

Concept 43.2 Births Increase and Deaths Decrease Population Size

Change in population size depends on the number of births and deaths over a given time.

“Birth–death” or BD model of population change:

DBNN tt 1

Concept 43.2 Births Increase and Deaths Decrease Population Size

Population growth rate (how fast it is changing):

DBNNN tt 1

DBDB

tt

DB

T

N

1)1(

Concept 43.2 Births Increase and Deaths Decrease Population Size

Per capita birth rate (b)—number of offspring an average individual produces

Per capita death rate (d)—average individual’s chance of dying

Per capita growth rate (r) = (b – d) = average individual’s contribution to total population growth rate

rNT

N

Concept 43.2 Births Increase and Deaths Decrease Population Size

If b > d, then r > 0, and the population grows.

If b < d, then r < 0, and the population shrinks.

If b = d, then r = 0, and population size does not change.

Apply the Concept, Ch. 43, p. 845

Figure 43.3 Life History of the Black-Legged Tick

Figure 43.3 Life History of the Black-Legged Tick

Table 43.1 Life Table for the 1978 Cohort of Cactus Ground Finch on Isla Daphne

Figure 43.4 Resource Acquisition Increases with Resource Availability

Figure 43.4 Resource Acquisition Increases with Resource Availability

Figure 43.4 Resource Acquisition Increases with Resource Availability (Part 1)

Figure 43.4 Resource Acquisition Increases with Resource Availability (Part 2)

Figure 43.4 Resource Acquisition Increases with Resource Availability (Part 3)

Figure 43.4 Resource Acquisition Increases with Resource Availability (Part 4)

Figure 43.5 The Principle of Allocation

Figure 43.5 The Principle of Allocation

Figure 43.6 Climate Warming Stresses Spiny Lizards

Figure 43.6 Climate Warming Stresses Spiny Lizards (Part 1)

Figure 43.6 Climate Warming Stresses Spiny Lizards (Part 2)

Figure 43.7 Environmental Conditions Affect Per Capita Growth Rates and Species Distributions

Figure 43.7 Environmental Conditions Affect Per Capita Growth Rates and Species Distributions (Part 1)

Figure 43.7 Environmental Conditions Affect Per Capita Growth Rates and Species Distributions (Part 2)

In-Text Art, Ch. 43, p. 850

In-Text Art, Ch. 43, p. 850

In-Text Art, Ch. 43, p. 851

In-Text Art, Ch. 43, p. 851

Concept 43.4 Populations Grow Multiplicatively, but Not for Long

r decreases as the population becomes more crowded; r is density dependent.

As the population grows and becomes more crowded, birth rates tend to decrease and death rates tend to increase.

When r = 0, the population size stops changing—it reaches an equilibrium size called carrying capacity, or K.

Concept 43.5 Extinction and Recolonization Affect Population Dynamics

Regional populations (metapopulations) are made up of subpopulations in habitat patches.

Individuals may move in or out of subpopulations.

Concept 43.5 Extinction and Recolonization Affect Population Dynamics

The BIDE model of popultion growth adds the number of immigrants (I) and emigrants (E) to the BD growth model.

EDIBNN tt 1

Apply the Concept, Ch. 43, p. 851

Figure 43.8 Per Capita Growth Rate Decreases with Population Density

Figure 43.8 Per Capita Growth Rate Decreases with Population Density (Part 1)

Figure 43.8 Per Capita Growth Rate Decreases with Population Density (Part 2)

Figure 43.8 Per Capita Growth Rate Decreases with Population Density

Figure 43.9 Human Population Growth

Figure 43.9 Human Population Growth (Part 1)

Figure 43.9 Human Population Growth (Part 2)

Figure 43.10 A Metapopulation Has Many Subpopulations

Apply the Concept, Ch. 43, p. 855

Figure 43.11 Corridors Can Rescue Some Populations (Part 1)

Figure 43.11 Corridors Can Rescue Some Populations (Part 2)

Figure 43.12 A Corridor for Large Mammals