Transcript Prentice Hall Biology

Section Outline
Section 5-1
5–1 How Populations Grow
A. Characteristics of Populations
B. Population Growth
C. Exponential Growth
D. Logistic Growth
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5-1 How Populations Grow
Population - group of organisms belonging to a single species that lives in
a given area.
3 Characteristics of any Population
1. Geographic distribution – area inhabited by population
2. Density - # per unit of space
3. Growth rate – how fast it grows
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Population Growth
Four factors that influence population size
1. Birth – duh.
2. Mortality - death
3. Emigration – out of an area
4. Immigration – into an area
•
•
When these factors are balanced = no growth (negative or positive)
What factors would increase size? Decrease size?
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What environmental factors influence these?
•Birth and immigration?
– Abundance of resources (food, mates, shelter)
– Organisms reproduce and move into the area for the
resources
•Mortality and emigration?
– Resources on the decline
– Organisms faced with dilemmas
• Adapt to other resources
• Death/extinction
• Move out - emigrate
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Exponential Growth
•Bacteria reproduce on average every 20 minutes
•In a matter of 1day, one bacteria reproduce into….
– 4720000000000000000000 bacteria
– mass of bacteria size of earth in 3 days
•Represented with a “J-curve©”
•Only occurs under ideal conditions (unlimited resources/no predation)
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9000000
Number of bacteria
8000000
Exponential Growth Chart
7000000
6000000
5000000
4000000
3000000
2000000
1000000
0
1
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3
5
7
9 11 13 15 17 19 21 23
Hours
Logistic Growth
•Normal growth curves
•Populations that grow exponentially use resources exponentially!
– “carrying capacity”
– The limit to which any population ceases to grow due to
depletion of resources
• Run out of food
• Nowhere to live
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Figure 5-4 Logistic Growth of Yeast Population
Section 5-1
Carrying capacity
Time (hours)
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Concept Map
Section 5-1
Population
Growth
can be
Logistic
growth
Exponential
growth
characterized by
No limits on
growth
Unlimited
resources
represented by
Constant
growth rate
J-shaped
curve
characterized by
Limits on
growth
which cause a
Falling
growth rate
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represented by
S-shaped
curve
Interest Grabber
Section 5-2
Name That Resource!
A situation that causes the growth of a population to decrease is called a
limiting factor. Some limiting factors depend on the size of the population.
Other limiting factors affect all populations in similar ways, regardless of
the population size.
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Interest Grabber continued
Section 5-2
1. Imagine a small island that has a population of five rabbits. How might
each of the following factors affect the rabbit population?
a. climate
b. food supply
c. predation
2. Now imagine another small island that has a population of 500 rabbits.
How would the same factors affect this population?
3 Which of the factors depend on population size? Which factors do not
depend on population size?
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Section Outline
Section 5-2
5–2 Limits to Growth
A.Limiting Factors
B.Density-Dependent Factors
1. Competition
2. Predation
3. Parasitism and Disease
C. Density-Independent Factors
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Limiting Factors
• Factors that influence negative population growth
• can be anything from….
– Climate
– Predators
– Food availability
– Parasites
– Human influences
• Clearing of forests – destroy natural habitat
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Density-Dependent Factors
•Any factor that is influenced by the
density of the population.
•Competition
– When populations become
crowded, resources are used up
at a faster rate.
– Occurs within species as well as
among groups of species.
– Species that compete will change
to ease the competition
– Drives evolution
• Ex: plants and sunlight
(canopies/black walnut)
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A Density-Dependent Limiting Factor
Section 5-2
Growth of Aphids
Exponential growth
Peak population
size
Rapid decline
Steady population
size
Steady population
size
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•Predation
– Predator-prey relationship – regulation of populations by
predators
– Most effective population control “technique”
– Ex: wolves and moose in Isle Royale
– Graph usually fluctuates often over time
• Predator and prey charts are inverse of each other
60
2400
50
2000
40
1600
30
1200
20
800
10
400
0
1955 1960
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0
1965
1970
1975
Moose
1980
Wolves
1985
1990
1995
Parasitism and Disease
•Disease and parasites very effective
– Ability to spread directly related
to density of population
• Higher density = faster
spread = higher death rate
– May be what eventually causes
human population decline
• Ex: Bubonic plague
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Density – Independent Factors
•Factors not caused by population size
– Climatic change
– Human disturbances
• Damming rivers, clearing forests
•Most populations will shrink in response
– Unless these events are recurring or large in
magnitude
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Interest Grabber
Section 5-3
How Fast Are We Growing?
Until about 500 years ago, the world’s human population remained fairly
stable. Then, as advances in medicine, agriculture, and technology
occurred, the human population began growing very rapidly. Today, the
world’s human population is greater than 6 billion people, and it continues
to grow, but at a slower rate.
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Interest Grabber continued
Section 5-3
1. The human population is increasing by about 1.4 percent each year.
Assume that the population is 6 billion (6,000,000,000). How large will
the population be in one year?
2. If the human population continues to grow at a rate of 1.4 percent per
year, the population would double in size (to 12 billion people) in only
51 years! What effect might this increase in population have on the
environment and on other people?
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Section Outline
Section 5-3
5–3 Human Population Growth
A.Historical Overview
B.Patterns of Population Growth
1.The Demographic Transition
2.Age Structure
C.Future Population Growth
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Historical Overview
• Populations of humans were regulated by the same limiting
factors influencing other animals.
– Harsh climate
– Food supply
– Predators
•50% infant mortality rate as soon as 500 years ago.
•8500 years ago – agriculture
– Now instead of nomads, humans domesticated in one area
– Increased the food supply
– Coupled with high birth rate already, population increased
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Human Population Growth
Section 5-3
Industrial
Revolution
begins
Agriculture
begins
Bubonic
plague
Plowing
and
irrigation
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Patterns of Population Growth
•Human populations will cease to grow exponentially because of
lack of resources.
•Today’s limiting factors:
– Disease
– Famine
– War
•Demography – study of human populations
•Examine:
– Birth rates
– Death rates
– Age structure
•Can predict future trends in growth or decline of population
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Demographic Transition
•When the demography shifts in a population
– Go from high birth rate/high death rate to….
– Low birth rate/low death rate
•How does a society do that?
•Occurred in the United States, Japan, and Europe
•Africa, S. America, and Asia, still have exponential growth….world
overall still growing exponentially.
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United States
Demographic
Transition
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Figure 5-13 Age Distribution
Section 5-3
U.S. Population
Males
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Females
Rwandan Population
Males
Females
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What Can Age Structure Diagrams Tell Us?
•Trends by….
– Age group
– Gender
– Birth rate
– Life Expectancy
•Overall quality of life
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Future Population Growth
•By 2050 population may increase to 9 billion
•Growth rate will slow to 0.43% from 1.4%
currently and 2.1% in the ’60’s.
•Some feel this is very bad for the
environment
•Others feel technology and changes in
society will allow us to cope.
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Go Online
Links from the authors on the gray wolf
Interactive test
For links on populations, go to www.SciLinks.org and enter the Web
Code as follows: cbn-2051.
For links on population growth, go to www.SciLinks.org and enter the
Web Code as follows: cbn-2053.
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