1. Population Ecology
Chapter 45

2. Population Ecology
Certain ecological principles govern the growth and sustainability of all populations--including human populations

3. Limits to Growth
A population’s growth depends on the resources of its environment
Moose/Wolf study on Isle Royal

4. Human Population Problems
Over 6 billion people alive
About 2 billion live in poverty
Most resources are consumed by the relatively few people in developed countries

5. Population
A group of individuals of the same species occupying a given area
Can be described by demographics
Vital statistics such as size, density, distribution, and age structure

6. Population Age Structure
Divide population into age categories
Population’s reproductive base includes members of the reproductive and pre-reproductive age categories

7. Density & Distribution
Number of individuals in some specified area of habitat
Crude density information is more useful if combined with distribution data
clumped
nearly uniform
Figure 45.2
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random

8. Determining Population Size
Direct counts are most accurate but seldom feasible
Can sample an area, then extrapolate
Capture-recapture method is used for mobile species

9. Capture-Recapture Method
Capture, mark, and release individuals
Return later and capture second sample
Count the number of marked individuals and use this to estimate total population

10. Assumptions in Capture-Recapture
Marking has no effect on mortality
Marking has no effect on likelihood to being captured
There is no immigration or emigration between sampling times

11. Changes in Population Size
Immigration adds individuals
Emigration subtracts individuals
Births add individuals
Deaths subtract individuals

12. Zero Population Growth
Interval in which number of births is balanced by number of deaths
Assume no change as a result of migration
Population size remains stable

13. Per Capita Rates Rates per individual
Total number of events in a time interval divided by the number of individuals
Per capita birth rate per month =
Number of births per month
Population size

14. r Net reproduction per individual per unit time
Variable combines per capita birth and death rates (assuming both constant)
Can be used to calculate rate of growth of a population

15. Exponential Growth Equation
G = rN
G is population growth per unit time
r is net reproduction per individual per unit time
N is population size

16. Exponential Growth
Population size expands by ever increasing increments during successive intervals
The larger the population gets, the more individuals there are to reproduce
Figure 45.4
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17. Effect of Deaths
Population grows exponentially as long as per capita death rates are lower than per capita birth rates
25% mortality between divisions
Figure 45.5
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18. Biotic Potential
Maximum rate of increase per individual under ideal conditions
Varies between species
In nature, biotic potential is rarely reached

19. Limiting Factors Any essential resource that is in short supply
All limiting factors acting on a population dictate sustainable population size

20. Carrying Capacity (K)
Maximum number of individuals that can be sustained in a particular habitat
Logistic growth occurs when population size is limited by carrying capacity

21. Logistic Growth Equation
G = rmax N (K-N/K)
G = population growth per unit time
rmax = maximum population growth rate per unit time
N = number of individuals
K = carrying capacity

22. Logistic Growth
As size of the population increases, rate of reproduction decreases
When the population reaches carrying capacity, population growth ceases

23. initial carrying capacity
Logistic Growth Graph
initial carrying capacity
new carrying capacity
Figure 45.6
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24. Overshooting Capacity
Population may temporarily increase above carrying capacity
Overshoot is usually followed by a crash; dramatic increase in deaths
Reindeer on St. Matthew’s Island
Figure 45.6
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25. Density-Dependent Controls
Logistic growth equation deals with density-dependent controls
Limiting factors become more intense as population size increases
Disease, competition, parasites, toxic effects of waste products

26. Density-Independent Controls
Factors unaffected by population density
Natural disasters or climate changes affect large and small populations alike

27. Life History Patterns
Patterns of timing of reproduction and survivorship
Vary among species
Summarized in survivorship curves and life tables

28. Life Table Tracks age-specific patterns
Population is divided into age categories
Birth rates and mortality risks are calculated for each age category

29. Graph of age-specific survivorship
Survivorship Curves
Graph of age-specific survivorship
Figure 45.8
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30. Predation and Life History
Guppy populations vary in life history characteristics and morphology
Differences have genetic basis
Variation seems to be result of directional selection by predators

31. Human Population Growth
Population now exceeds 6 billion
Rates of increase vary among countries
Average annual increase is 1.26 percent
Population continues to increase exponentially

32. Side-Stepping Controls
Expanded into new habitats
Agriculture increased carrying capacity; use of fossil fuels aided increase
Hygiene and medicine lessened effects of density-dependent controls

33. Future Growth Exponential growth cannot continue forever
Breakthroughs in technology may further increase carrying capacity
Eventually, density-dependent factors will slow growth

34. Fertility Rates Worldwide, average annual rate of increase is 1.26%
Total fertility rate (TFR) is average number of children born to a woman
Highest in developing countries, lowest in developed countries

35. Age Structure Diagrams
Show age distribution of a population
Figure 45.14
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Slow
Growth
Zero
Growth
Negative
Growth
Rapid
Growth

36. Population Momentum
Lowering fertility rates cannot immediately slow population growth rate
Why? There are already many future parents alive
If every couple had just two children, population would still keep growing for another 60 years

37. Slowing Growth in China
World’s most extensive family planning program
Government rewards small family size, penalizes larger families, provides free birth control, abortion, sterilization
Since 1972, TFR down to 1.8 from 5.7

38. Effects of Economic Development
Total fertility rates (TFRs) are highest in developing countries, lowest in developed countries
When individuals are economically secure, they are under less pressure to have large families

39. Population Sizes in 2001 Asia 3.7 billion Europe 727 million
Africa million
Latin America 525 million
North America 316 million
Oceania 31 million

40. Resource Consumption
United States has 4.7 percent of the world’s population
Americans have a disproportionately large effect on the world’s resources
Per capita, Americans consume more resources and create more pollution than citizens of less developed nations