objectives 1.explain the characteristics used to describe a population. 2.explain factors that...
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Objectives
1. Explain the characteristics used to describe a population.
2. Explain factors that affect population size.
3. Explain exponential and logistic growth.
4. Define the following:
A. Population density
B. Immigration
C. Emigration
D. Carrying capacity
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Characteristics of Populations
1. Geographic distribution – the area inhabited by a population
2. Density – number of individuals per unit area
3. Growth rate
4. Age structure
Math Connections
Population density = Number of Individuals/Unit area
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Suppose there are 150 bullfrogs living in a pond that covers an area of 3 square kilometers. What is the density of the bullfrog population?
150 divided by 3 = 50 bullfrogs per square kilometer
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Factors that Affect Population Size
1. Number of births
2. Number of deaths
3. Number of individuals that enter or leave the population
A. Immigration – movement of individuals into an area
B. Emigration – movement of individuals out of a population
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Population Growth
Exponential Growth
A. Occurs under ideal conditions with unlimited resources
(Abundance of food, water, and shelter; absence of predation and
disease)
B. Population reproduces at a constant rate
Logistic Growth
A. Occurs when a population’s growth slows or stops following a period
of exponential growth
B. Resources become less available
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Carrying Capacity
Carrying capacity is the largest number of individuals that a given environment can support.
What is the growth rate if a particular species reaches its carrying capacity in a given environment?
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PopulationGrowth
can be
represented bycharacterized by characterized by represented by
which cause a
Exponentialgrowth
Logisticgrowth
Fallinggrowth rate
S-shapedcurve
Limits ongrowth
No limits on growth
J-shapedcurve
Constantgrowth rate
Unlimitedresources
Section 5-1
Concept Map
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Nu m
ber
of Y
east
Cel
l s
Time (hours)
Carrying capacity
Section 5-1
Figure 5-4 Logistic Growth of Yeast Population
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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.
Section 5-2
Interest Grabber
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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?
Section 5-2
Interest Grabber continued
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Name that Resource!1. All of these factors could limit this population. The food supply would have to dwindle substantially in order for it to affect only five rabbits. One predator could wipe out the entire population of five rabbits.
2. Predation and the availability of food will have more of an effect on this population than the smaller one because there are more rabbits to be preyed upon and to compete for the food.
3. The factors that depend on population size include the competition for food and predation. The factor that does not depend on population size is climate.
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Objectives
1. Explain factors that limit population growth.
2. Define the following:
A. Limiting factor
B. Density-dependent limiting factor
C. Predator-prey relationship
D. Density-independent limiting factor
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Limits to Growth
Density-Dependent Factors – depend on population size
1. Competition – Crowded; organisms struggle with one another for
food, water, space, sunlight, and other essentials of life
Note: Competition can also occur between members of
different species. This type of competition is a major
force behind evolutionary change.
2. Predation (Examples: relationships between sea otters and sea
urchins and sea otters and killer whales)
3. Parasitism and Disease
Density-Independent Factors – unusual weather, natural disasters, seasonal cycles, certain human activities
Section 5-2
Section Outline
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Growth of Aphids
Exponential growth
Steady populationsize
Peak populationsize
Rapid decline
Steady populationsize
Section 5-2
A Density-Dependent Limiting Factor
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60
50
40
30
20
10
01955 1960 1965 1970 1975 1980 1985 1990 1995
2000
1600
1200
800
400
0
2400
Moose Wolves
Section 5-2
Figure 5-7 Wolf and Moose Populations on Isle Royale
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Wolf and Moose
1. What density-dependent factors may have caused the crash in the wolf population?
Decline in the moose population 2. What density-independent factors may have caused the crash in the
wolf population? Unusually deep winter snows could have made it difficult for the wolf to
hunt, parasites or disease could have weakened or killed the wolves3. How are the increases and decreases in the moose population related
to changes in the wolf population? As the moose population increased, the wolf population increased. Decreases in the moose population were followed by decreases in the
wolf population.
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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.
Section 5-3
Interest Grabber
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Objectives
1. Describe how the size of the human population has changed over time.
2. Explain why population growth rates differ in countries throughout the world.
3. Define the following:
A. Demography
B. Demographic Transition
C. Age-structure diagram
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Demography – the scientific study of human populations
Demographic transition – change in a population from high birth and death rates to low birth and death rates
Age-structure diagram – graphs that represent the numbers of people in different age groups in a population
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Agriculturebegins
Plowingand irrigation
Bubonicplague
IndustrialRevolutionbegins
Section 5-3
Human Population Growth
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Important People:
Dr. Leila Denmark – oldest practicing physician in the United States;
helped invent the whooping cough vaccine in 1936
Connections to Economics:
Two centuries ago, English economist Thomas Malthus observed that human populations were growing rapidly. He predicted that such growth would not continue indefinitely. According to Malthus, famine and disease would limit human population growth.
Today, scientists have identified a variety of other social and economic factors that can affect human populations.
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U.S. Population Rwandan PopulationMales MalesFemales Females
Section 5-3
Figure 5-13 Age Distribution
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How do the United States and Rwanda differ in the percentages of 10-14 year olds in the population?
In the United States, 10-14 year olds make up about 6.5% of the population, and in Rwanda they make up about 14% of the population. The difference is about 7.5% - about 3.5 percentage points for males and 4 percentage points for females.