1. Chapter 52 (pgs. 1151- 1172) Population Ecology
AP minknow
How density, dispersion, and demographics can describe a population.
The differences between exponential and logistic models of population growth.
How density-dependent and density-independent factors can control population growth

2. Characteristics of Populations
1.Define the scope of population ecology 
2.Define and distinguish between density and dispersion. 
3.Explain how ecologists measure the density of a species. 
4.Describe conditions that may result in the clumped dispersion, uniform dispersion, and random dispersion of populations. 
5.Describe the characteristics of populations that exhibit Type I, Type II, and Type III survivorship curves.  
6.Describe the characteristics of populations that exhibit Type I, Type II, and Type III survivorship curves.
Life History Traits
7.Define and distinguish between semelparity and iteroparity. 
8.Explain how limited resources affect life histories. 
9.Give examples of the trade-off between reproduction and survival.

3. Population Growth
10.Compare the geometric model of population growth with the logistic model.  
11.Explain how an environment's carrying capacity affects the intrinsic rate of increase of a population. 
12.Distinguish between r-selected populations and K-selected populations. 
13.Explain how a "stressful" environment may alter the standard r-selection and K-selection characteristics.
Population-Limiting Factors
14.Explain how density-dependent factors affect population growth. 
15.Explain how density-dependent and density-independent factors may work together to control a population's growth. 
16.Explain how predation can affect life history through natural selection. 
17.Describe several boom-and-bust population cycles, noting possible causes and consequences of the fluctuations.
Human Population Growth
18.Describe the history of human population growth. 
19.Define the demographic transition. 
20.Compare the age structures of Italy, Kenya, and the United States. Describe the possible consequences for each country. 
21.Describe the problems associated with estimating Earth's carrying capacity.

4. Population ecology is the study of populations in relation to environment
Including environmental influences on population density and distribution, age structure, and variations in population size

5. 52.1: Dynamic biological processes influence population density, dispersion, and demography A population
A population
Is a group of individuals of a single species living in the same general area

6. Density and Dispersion
Is the number of individuals per unit area or volume
Dispersion
Is the pattern of spacing among individuals within the boundaries of the population

7. Density: A dynamic perspective.
Births and immigration add individuals to a population.
Births
Immigration
PopuIation size
Emigration
Deaths
Deaths and emigration remove individuals from a population.
Determining the density of natural populations
Is possible, but difficult to accomplish
In most cases
It is impractical or impossible to count all individuals in a population
Density is the result of a dynamic interplay
Between processes that add individuals to a population and those that remove individuals from it

8. Patterns of Dispersion
Environmental and social factors
Influence the spacing of individuals in a population.
There are three different Patterns of Dispersion
Clumped Dispersion
Uniform Dispersion
Random Dispersion

9. A clumped dispersion Is one in which individuals aggregate in patches
May be influenced by resource availability and behavior
Figure 52.3a
(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.

10. A uniform dispersion
Is one in which individuals are evenly distributed
May be influenced by social interactions such as territoriality
Figure 52.3b
(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.

11. A random dispersion
Is one in which the position of each individual is independent of other individuals
Figure 52.3c
(c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

12. Life Tables A life table
Is an age-specific summary of the survival pattern of a population
Is best constructed by following the fate of a cohort

13. Survivorship Curves A survivorship curve
Is a graphic way of representing the data in a life table
Figure 52.4
1000
100 10 1
Number of survivors (log scale) 2 4 6 8
Age (years)
Males
Females

14. Survivorship curves can be classified into three general types
Type I, Type II, and Type III I II
III 50
100 1 10
1,000
Percentage of maximum life span
Number of survivors (log scale)
Many species fall somewhere between these basic types of survivorship curves.
Some invertebrates, such as crabs, show a “stair-stepped” curve, with increased mortality during molts.
Figure 52.5

15. 52.2 Life histories are highly diverse, but they exhibit patterns in their variability.
Life histories entail three basic variables:
when reproduction begins
how often the organism reproduces
how many offspring are produced during each reproductive episode.
These histories are evolutionary outcomes reflected in the development, physiology, and behavior of an organism.
Some organisms, such as the agave plant, exhibit semelparity. Big Bang Production. (then death)
By contrast, some organisms exhibit iteroparity.
They produce only a few offspring during repeated reproductive episodes.

16. Some plants produce a large number of small seeds
Ensuring that at least some of them will grow and eventually reproduce
Figure 52.8a
(a) 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.

17. Other types of plants produce a moderate number of large seeds
That provide a large store of energy that will help seedlings become established
Figure 52.8b
(b) 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.

18. What factors contribute to the evolution of semelparity versus iteroparity?
In other words, how much does an individual gain in reproductive success through one pattern versus the other?
The critical factor is survival rate of the offspring.
When the survival of offspring is low, as in highly variable or unpredictable environments, big-bang reproduction (semelparity) is favored.
Repeated reproduction (iteroparity) is favored in dependable environments where competition for resources is intense.
In such environments, a few, well-provisioned offspring have a better chance of surviving to reproductive age.

19. Population Growth is measured by Per Capita Rate of Increase
If immigration and emigration are ignored
A population’s growth rate (per capita increase) equals birth rate minus death rate
Growth rate = rN
It can be found using the equation--- dN dt  rN

20. Exponential Population Growth
Is population increase under idealized conditions
Under these conditions
The rate of reproduction is at its maximum, called the intrinsic rate of increase
Exponential population growth
Results in a J-shaped curve
Figure 52.9 5 10 15
500
1,000
1,500
2,000
Number of generations
Population size (N) dN dt 
1.0N
0.5N dN dt 
rmaxN

21. The J-shaped curve of exponential growth
Is characteristic of some populations that are rebounding
Figure 52.10
1900
1920
1940
1960
1980
Year
2,000
4,000
6,000
8,000
Elephant population

22. 52.4: The logistic growth model includes the concept of carrying capacity
Exponential growth
Cannot be sustained for long in any population
A more realistic population model
Limits growth by incorporating carrying capacity
Carrying capacity (K)
Is the maximum population size the environment can support

23. The Logistic Growth Model
In the logistic population growth model
The per capita rate of increase declines as carrying capacity is reached
We construct the logistic model by starting with the exponential model
And adding an expression that reduces the per capita rate of increase as N increases
Maximum
Positive
Negative
N  K
Population size (N)
Per capita rate of increase (r)

24. The logistic growth equation
Table 52.3
Includes K, the carrying capacity dN dt 
(K  N) K
rmax N

25. The logistic model of population growth
Produces a sigmoid (S-shaped) curve dN dt 
1.0N
Exponential growth
Logistic growth
1,500  N
1,500
K  1,500 5 10 15
500
1,000
2,000
Number of generations
Population size (N)
Figure 52.12

26. As N approaches K for a certain population, which of the following is predicted by the logistic equation?
The growth rate will not change.
The growth rate will approach zero.
The population will show an Allee effect.
The population will increase exponentially.
The carrying capacity of the environment will increase.
Answer: b
Source: Barstow - Test Bank for Biology, Sixth Edition, Question #29.

27. The Logistic Model and Real Populations
800
600
400
200
Time (days) 5 10 15
1,000
Number of Paramecium/ml
The growth of laboratory populations of paramecia
Fits an S-shaped curve
Some populations overshoot K
Before settling down to a relatively stable density
Some populations
Fluctuate greatly around K
180
150
120 90 60 30
Time (days)
160
140 80
100 40 20
Number of Daphnia/50 ml 80 60 40 20
1975
1980
1985
1990
1995
2000
Time (years)
Number of females

28. The Logistic Model and Life Histories
Life history traits favored by natural selection
May vary with population density and environmental conditions
K-selection, or density-dependent selection
Selects for life history traits that are sensitive to population density
K-selection tends to maximize population size and operates in populations living at a density near K.
r-selection, or density-independent selection
Selects for life history traits that maximize reproduction
r-selection tends to maximize r, the rate of increase, and occurs in environments in which population densities fluctuate well below K, or when individuals face little competition.
Controversy

29. Density-dependent birth rate
52.5: Populations are regulated by a complex interaction of biotic and abiotic influences
In density-independent populations
Birth rate and death rate do not change with population density
In density-dependent populations
Birth rates fall and death rates rise with population density
Determining equilibrium for population density
Figure 52.14a–c
Density-dependent birth rate
Density-dependent death rate
Equilibrium density
Density-independent death rate
Density-independent birth rate
Population density
Birth or death rate per capita
(a) Both birth rate and death rate change with population density.
(b) Birth rate changes with population density while death rate is constant.
(c) Death rate changes with population density while birht rate is constant.

30. Density-Dependent Population Regulation
Density-dependent birth and death rates
Are an example of negative feedback that regulates population growth
Are affected by many different mechanisms
Competition for Resources
Territoriality
Health (Disease/Parasites)
Predation
Toxic Wastes (think bacteria)

31. Competition for Resources
In crowded populations, increasing population density
Intensifies intraspecific competition for resources 10
100
1,000
10,000
Average number of seeds per reproducing individual (log scale)
Average clutch size
Seeds planted per m2
Density of females 70 20 30 40 50 60 80
2.8
3.0
3.2
3.4
3.6
3.8
4.0
(a) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases.
(b) Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply.

32. Territoriality Cheetahs are highly territorial
Using chemical communication to warn other cheetahs of their boundaries
Figure 52.16

33. Population Dynamics The study of population dynamics
Focuses on the complex interactions between biotic and abiotic factors that cause variation in population size

34. Stability and Fluctuation
Long-term population studies
Have challenged the hypothesis that populations of large mammals are relatively stable over time
Figure 52.18
The pattern of population dynamics observed in this isolated population indicates that various biotic and abiotic factors can result in dramatic fluctuations over time in a moose population.
Researchers regularly surveyed the population of moose on Isle Royale, Michigan, from 1960 to During that time, the lake never froze over, and so the moose population was isolated from the effects of immigration and emigration.
FIELD STUDY
Over 43 years, this population experienced two significant increases and collapses, as well as several less severe fluctuations in size.
RESULTS
CONCLUSION
1960
1970
1980
1990
2000
Year
Moose population size
500
1,000
1,500
2,000
2,500
Steady decline probably caused largely by wolf predation
Dramatic collapse caused by severe winter weather and food shortage, leading to starvation of more than 75% of the population

35. Commercial catch (kg) of male crabs (log scale)
Extreme fluctuations in population size Are typically more common in invertebrates than in large mammals
Figure 52.19
1950
1960
1970
1980
Year
1990
10,000
100,000
730,000
Commercial catch (kg) of male crabs (log scale)
Fluctuating Wind pushing eggs out to sea
Cannibalism

36. Metapopulations and Immigration
Are groups of populations linked by immigration and emigration
High levels of immigration combined with higher survival
Can result in greater stability in populations
Mandarte island
Small islands
Number of breeding females
1988
1989
1990
1991
Year 10 20 30 40 50 60

37. Population Cycles Many populations
Undergo regular boom-and-bust cycles
Figure 52.21
Year
1850
1875
1900
1925 40 80
120
160 3 6 9
Lynx population size (thousands)
Hare population size (thousands)
Lynx
Snowshoe hare
Three main hypotheses have been proposed to explain the lynx/hare cycles.
The cycles may be caused by food shortage during winter.
The cycles may be due to predator-prey interactions.
The cycles may be affected by a combination of food resource limitation and excessive predation.

38. Limiting Factors
Density Dependant Factors
Density Independent Factors

39. No population can grow indefinitely
52.6: Human population growth has slowed after centuries of exponential increase
No population can grow indefinitely
And humans are no exception
The Global Human Population
8000 B.C.
4000 B.C.
3000 B.C.
2000 B.C.
1000 B.C.
1000 A.D.
The Plague
Human population (billions)
2000 A.D. 1 2 3 4 5 6
Increased relatively slowly until about 1650 and then began to grow exponentially

40. Global population Growth Rate
Though the global population is still growing
The rate of growth began to slow approximately 40 years ago
Figure 52.23
1950
1975
2000
2025
2050
Year
2003
Percent increase
2.2 2
1.6
1.4
1.2 1
0.8
0.6
0.4
0.2
1.8

41. Age Structure
One important demographic factor in present and future growth trends
Is a country’s age structure, the relative number of individuals at each age
Usually presented in Pyramids
Figure 52.25
Rapid growth Afghanistan
Slow growth United States
Decrease Italy
Male
Female
Age 8 6 4 2
Percent of population
80–84
85
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
20–24
25–29
10–14
5–9
0–4
15–19

42. Infant Mortality and Life Expectancy
Infant mortality and life expectancy at birth
Vary widely among developed and developing countries but do not capture the wide range of the human condition
Figure 52.26
Developed countries
Developing countries
Infant mortality (deaths per 1,000 births)
Life expectancy (years) 60 50 40 30 20 10 80

43. Global Carrying Capacity
Just how many humans can the biosphere support?
It is complex and we just don’t know, but we have….

44. Ecological Footprint The ecological footprint concept
Figure 52.27 16 14 12 10 8 6 4 2
New Zealand
Australia
Canada
Sweden
World
China
India
Available ecological capacity (ha per person)
Spain UK
Japan
Germany
Netherlands
Norway
USA
Ecological footprint (ha per person)
The ecological footprint concept
Summarizes the aggregate land and water area needed to sustain the people of a nation
Is one measure of how close we are to the carrying capacity of Earth
At more than 6 billion people
The world is already in ecological deficit