populations chapter 5. 5.1 how populations grow learning targets 5.1 what characteristics are used...
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PopulationsPopulationsChapter 5Chapter 5
5.1 How Populations Grow5.1 How Populations Grow
Learning Targets 5.1Learning Targets 5.1
What characteristics are used to describe a population?
What factors affect population size?
What are exponential growth and logistic growth?
Characteristics of Populations
Characteristics of Populations
– What characteristics are used to describe a population?
– What characteristics are used to describe a population?
Characteristics of Populations
Characteristics of Populations
• Characteristics of Populations– Three important characteristics of a
population are its:•geographic distribution•density•growth rate
• Characteristics of Populations– Three important characteristics of a
population are its:•geographic distribution•density•growth rate
Geographic DistributionGeographic Distribution• Geographic distribution, or range,
describes the area inhabited by a population.
• Geographic distribution, or range, describes the area inhabited by a population.
Density:Density:
• Population density is the number of individuals per unit area.
• Population density is the number of individuals per unit area.
Growth RateGrowth Rate
• Growth rate is the increase or decrease of the number of individuals in a population over time.
• Growth rate is the increase or decrease of the number of individuals in a population over time.
Population GrowthPopulation Growth
– What factors affect population size?– What factors affect population size?
Population GrowthPopulation Growth
• Population Growth– Three factors can affect population size:
• the number of births• the number of deaths• the number of individuals that enter or leave the
population
– A population can grow when its birthrate is greater than its death rate.
• Population Growth– Three factors can affect population size:
• the number of births• the number of deaths• the number of individuals that enter or leave the
population
– A population can grow when its birthrate is greater than its death rate.
Population GrowthPopulation Growth
• Immigration, the movement of individuals into an area, is another factor that can cause a population to grow.
• Populations can increase by immigration as animals in search of mates or food arrive from outside.
• Immigration, the movement of individuals into an area, is another factor that can cause a population to grow.
• Populations can increase by immigration as animals in search of mates or food arrive from outside.
Population GrowthPopulation Growth
• Emigration, the movement of individuals out of an area, can cause a population to decrease in size. Exit
• Emigration can occur when animals leave to find mates and establish new territories.
• A shortage of food in one area may also lead to emigration.
• Emigration, the movement of individuals out of an area, can cause a population to decrease in size. Exit
• Emigration can occur when animals leave to find mates and establish new territories.
• A shortage of food in one area may also lead to emigration.
Exponential GrowthExponential Growth
–What are exponential growth and logistic growth?–What are exponential growth and logistic growth?
Exponential GrowthExponential Growth
• Exponential Growth– Under ideal conditions with unlimited
resources, a population will grow exponentially.
– Exponential growth occurs when the individuals in a population reproduce at a constant rate.
– The population becomes larger and larger until it approaches an infinitely large size.
• Exponential Growth– Under ideal conditions with unlimited
resources, a population will grow exponentially.
– Exponential growth occurs when the individuals in a population reproduce at a constant rate.
– The population becomes larger and larger until it approaches an infinitely large size.
Exponential GrowthExponential GrowthExponential Growth
Logistic GrowthLogistic Growth
• Logistic Growth• In nature, exponential growth does not
continue in a population for very long.
• Logistic Growth• In nature, exponential growth does not
continue in a population for very long.
Logistic GrowthLogistic Growth
– As resources become less available, the growth of a population slows or stops.
– Logistic growth occurs when a population's growth slows or stops following a period of exponential growth.
– As resources become less available, the growth of a population slows or stops.
– Logistic growth occurs when a population's growth slows or stops following a period of exponential growth.
Logistic GrowthLogistic Growth• Logistic growth is characterized by an
S-shaped curve.• Logistic growth is characterized by an
S-shaped curve.
Logistic GrowthLogistic Growth– Carrying Capacity
• The largest number of individuals of a population that a given environment can support is called its carrying capacity.
• When a population reaches the carrying capacity of its environment, its growth levels off. The average growth rate is zero.
– Carrying Capacity• The largest number of individuals of a
population that a given environment can support is called its carrying capacity.
• When a population reaches the carrying capacity of its environment, its growth levels off. The average growth rate is zero.
Lets Review 5-1Lets Review 5-1
5-15-1– Population density is the number of
individualsa. that are born each year.b. per unit area.c. that immigrate.d. that emigrate.
– Population density is the number of individuals
a. that are born each year.b. per unit area.c. that immigrate.d. that emigrate.
5-15-1
– When the birthrate of a population exceeds its death rate, the population • decreases.• increases.• stays the same.• increases then decreases.
– When the birthrate of a population exceeds its death rate, the population • decreases.• increases.• stays the same.• increases then decreases.
5-15-1
– An S-shaped curve on a graph of population growth is characteristic of • exponential growth.• logistic growth.• carrying capacity.• delayed growth.
– An S-shaped curve on a graph of population growth is characteristic of • exponential growth.• logistic growth.• carrying capacity.• delayed growth.
5-15-1
– Exponential growth in a population slows down or stops as • resources become limited.• rate of immigration increases.• rate of emigration decreases.• birth rate increases.
– Exponential growth in a population slows down or stops as • resources become limited.• rate of immigration increases.• rate of emigration decreases.• birth rate increases.
5-15-1
– Exponential growth rate means that each new generation of a population• adds the same number of new individuals as
the previous generation did.• increases at the same rate as the previous
generation.• is the same size as the generation before.
• increases by a varying amount.
– Exponential growth rate means that each new generation of a population• adds the same number of new individuals as
the previous generation did.• increases at the same rate as the previous
generation.• is the same size as the generation before.
• increases by a varying amount.
END OF SECTION 5.1
END OF SECTION 5.1
5.2 Limits to Growth5.2 Limits to Growth
Learning Targets 5.2Learning Targets 5.2
What factors limit population growth?
Limiting FactorsLimiting Factors
– What factors limit population growth?– What factors limit population growth?
Limiting FactorsLimiting Factors
• Limiting Factors• The primary productivity of an ecosystem
can be reduced when there is an insufficient supply of a particular nutrient.
• Ecologists call such substances limiting nutrients.
• Limiting Factors• The primary productivity of an ecosystem
can be reduced when there is an insufficient supply of a particular nutrient.
• Ecologists call such substances limiting nutrients.
Limiting FactorsLimiting Factors
• A limiting nutrient is an example of a more general ecological concept: a limiting factor.
• In the context of populations, a limiting factor is a factor that causes population growth to decrease.
• A limiting nutrient is an example of a more general ecological concept: a limiting factor.
• In the context of populations, a limiting factor is a factor that causes population growth to decrease.
Density-Dependent FactorsDensity-Dependent Factors
• Density-Dependent Factors• A limiting factor that depends on population
size is called a density-dependent limiting factor.
• Density-Dependent Factors• A limiting factor that depends on population
size is called a density-dependent limiting factor.
Density-Dependent FactorsDensity-Dependent Factors
– Density-dependent limiting factors include: •competition•predation•parasitism•disease
– Density-dependent limiting factors include: •competition•predation•parasitism•disease
Density-Dependent FactorsDensity-Dependent Factors
– Density-dependent factors operate only when the population density reaches a certain level. These factors operate most strongly when a population is large and dense.
– They do not affect small, scattered populations as greatly.
– Density-dependent factors operate only when the population density reaches a certain level. These factors operate most strongly when a population is large and dense.
– They do not affect small, scattered populations as greatly.
Density-Dependent FactorsDensity-Dependent Factors
– Competition• When populations become crowded,
organisms compete for food, water space, sunlight and other essentials.
• Competition among members of the same species is a density-dependent limiting factor.
– Competition• When populations become crowded,
organisms compete for food, water space, sunlight and other essentials.
• Competition among members of the same species is a density-dependent limiting factor.
Density-Dependent FactorsDensity-Dependent Factors
• Competition can also occur between members of different species.
• This type of competition can lead to evolutionary change.
• Over time, the species may evolve to occupy different niches.
• Competition can also occur between members of different species.
• This type of competition can lead to evolutionary change.
• Over time, the species may evolve to occupy different niches.
Density-Dependent FactorsDensity-Dependent Factors
– Predation• Populations in nature are often controlled by
predation. • The regulation of a population by predation
takes place within a predator-prey relationship, one of the best-known mechanisms of population control.
– Predation• Populations in nature are often controlled by
predation. • The regulation of a population by predation
takes place within a predator-prey relationship, one of the best-known mechanisms of population control.
Density-Dependent FactorsDensity-Dependent Factors
Wolf and Moose Populations on Isle Royale
Moose Wolves
Density-Dependent FactorsDensity-Dependent Factors
– Parasitism and Disease• Parasites can limit the growth of a
population.• A parasite lives in or on another organism
(the host) and consequently harms it.
– Parasitism and Disease• Parasites can limit the growth of a
population.• A parasite lives in or on another organism
(the host) and consequently harms it.
Density-Independent FactorsDensity-Independent Factors
• Density-Independent Factors•Density-independent limiting factors
affect all populations in similar ways, regardless of the population size.
• Density-Independent Factors•Density-independent limiting factors
affect all populations in similar ways, regardless of the population size.
Density-Independent FactorsDensity-Independent Factors– Examples of density-independent limiting
factors include: •unusual weather
•natural disasters
•seasonal cycles
•certain human activities—such as damming rivers and clear-cutting forests
– Examples of density-independent limiting factors include: •unusual weather
•natural disasters
•seasonal cycles
•certain human activities—such as damming rivers and clear-cutting forests
Let’s Review 5-2Let’s Review 5-2
5-25-2
– A limiting factor that affects all populations in similar ways regardless of their size might be • drought.• disease.• predation.• crowding.
– A limiting factor that affects all populations in similar ways regardless of their size might be • drought.• disease.• predation.• crowding.
5-25-2
– Which of the following would be a limiting factor affecting the panda population of China?• programs that educate people about
endangered species• capture of some pandas for placement in
zoos• laws protecting habitat destruction• a disease that kills bamboo plants
– Which of the following would be a limiting factor affecting the panda population of China?• programs that educate people about
endangered species• capture of some pandas for placement in
zoos• laws protecting habitat destruction• a disease that kills bamboo plants
5-25-2
– Density-dependent factors operate most strongly when a population is • large and dense.• large but sparse.• small and sparse.• small, but growing.
– Density-dependent factors operate most strongly when a population is • large and dense.• large but sparse.• small and sparse.• small, but growing.
5-25-2
– Within a limited area, if the population of a predator increases, the population of its prey is likely to• increase.• decrease.• remain about the same.• become extinct.
– Within a limited area, if the population of a predator increases, the population of its prey is likely to• increase.• decrease.• remain about the same.• become extinct.
5-25-2
– Which of the following is a density-independent factor affecting populations?• predation• disease• a destructive hurricane• parasites
– Which of the following is a density-independent factor affecting populations?• predation• disease• a destructive hurricane• parasites
END OF SECTION 5.2
END OF SECTION 5.2
5.3 Human PopulationsAs of January 27, 2011 the world's population is estimated to be just
over 6.896 BILLION
The US Population alone is over 311 Million
5.3 Human PopulationsAs of January 27, 2011 the world's population is estimated to be just
over 6.896 BILLION
The US Population alone is over 311 Million
Learning Targets 5.3Learning Targets 5.3
How has the size of the human population changed over time?
Why do population growth rates differ in countries throughout the world?
5-3 Human Population
Growth
5-3 Human Population
Growth
Historical OverviewHistorical Overview
– How has the size of the human population changed over time?
– How has the size of the human population changed over time?
Historical OverviewHistorical Overview
• Historical Overview– Like the populations of many other living
organisms, the size of the human population tends to increase with time.
– For most of human existence, the population grew slowly.
– Limiting factors kept population sizes low.
• Historical Overview– Like the populations of many other living
organisms, the size of the human population tends to increase with time.
– For most of human existence, the population grew slowly.
– Limiting factors kept population sizes low.
Historical OverviewHistorical Overview• About 500 years ago, the human
population began growing more rapidly.• Life was made easier and safer by
advances in agriculture and industry.• Death rates were dramatically reduced
due to improved sanitation, medicine, and healthcare, while birthrates remained high.
• About 500 years ago, the human population began growing more rapidly.
• Life was made easier and safer by advances in agriculture and industry.
• Death rates were dramatically reduced due to improved sanitation, medicine, and healthcare, while birthrates remained high.
Historical OverviewHistorical Overview• With these advances, the human
population experienced exponential growth.
• With these advances, the human population experienced exponential growth. Human Population
Growth
Patterns of Population GrowthPatterns of Population Growth
• Patterns of Population Growth•The scientific study of human
populations is called demography. •Demography examines the
characteristics of human populations and attempts to explain how those populations will change over time.
• Patterns of Population Growth•The scientific study of human
populations is called demography. •Demography examines the
characteristics of human populations and attempts to explain how those populations will change over time.
Patterns of Population GrowthPatterns of Population Growth
– Why do population growth rates differ in countries throughout the world?
– What would cause these differences?
– Why do population growth rates differ in countries throughout the world?
– What would cause these differences?
Patterns of Population GrowthPatterns of Population Growth
– Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly.
– Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly.
Patterns of Population GrowthPatterns of Population Growth– The Demographic Transition
•Over the past century, population growth in the United States, Japan, and much of Europe has slowed dramatically.
•According to demographers, these countries have completed the demographic transition, a dramatic change in birth and death rates.
– The Demographic Transition•Over the past century, population
growth in the United States, Japan, and much of Europe has slowed dramatically.
•According to demographers, these countries have completed the demographic transition, a dramatic change in birth and death rates.
Patterns of Population GrowthPatterns of Population Growth• The demographic transition has three
stages.• In stage 1, there are high death rates and
high birthrates.• In stage 2, the death rate drops, while the
birthrate remains high. The population increases rapidly.
• In stage 3, the birthrate decreases, causing population growth to slow.
• The demographic transition has three stages.
• In stage 1, there are high death rates and high birthrates.
• In stage 2, the death rate drops, while the birthrate remains high. The population increases rapidly.
• In stage 3, the birthrate decreases, causing population growth to slow.
Patterns of Population Growth
Patterns of Population Growth• The
demographic transition is complete when the birthrate falls to meet the death rate, and population growth stops.
• The demographic transition is complete when the birthrate falls to meet the death rate, and population growth stops.
Check pointCheck point
• On a separate piece of paper, you and a partner write down the 3 stages of demographic transition.
• Predict what you think caused the population to slow in the US recently.
• On a separate piece of paper, you and a partner write down the 3 stages of demographic transition.
• Predict what you think caused the population to slow in the US recently.
Patterns of Population GrowthPatterns of Population Growth
– Age Structure• Population growth depends, in part, on how
many people of different ages make up a given population.
• Demographers can predict future growth using models called age-structure diagrams.
• Age-structure diagrams show the population of a country broken down by gender and age group.
– Age Structure• Population growth depends, in part, on how
many people of different ages make up a given population.
• Demographers can predict future growth using models called age-structure diagrams.
• Age-structure diagrams show the population of a country broken down by gender and age group.
Patterns of Population GrowthPatterns of Population Growth
• In the United States, there are nearly equal numbers of people in each age group.
• This age structure diagram predicts a slow but steady growth rate for the near future.
• In the United States, there are nearly equal numbers of people in each age group.
• This age structure diagram predicts a slow but steady growth rate for the near future.
Males Females
8 6 4 2 0 2 4 6 8
Percentage of Population
80+
60–64
20–24
0–4
40–44A
ge
(yea
rs)
U.S. Population
Patterns of Population GrowthPatterns of Population Growth• In Rwanda, there
are many more young children than teenagers, and many more teenagers than adults.
• This age structure diagram predicts a population that will double in about 30 years.
• In Rwanda, there are many more young children than teenagers, and many more teenagers than adults.
• This age structure diagram predicts a population that will double in about 30 years.
80+
60–64
20–24
0–4
Ag
e (y
ears
)
Males Females
Rwandan Population
40–44
Percentage of Population
Future Population GrowthFuture Population Growth
• Future Population Growth• To predict human population growth,
demographers must consider the age structure of each country, as well as the prevalence of life-threatening diseases.
• If growing countries move toward the demographic transition, growth rate may level off or decrease.
• Future Population Growth• To predict human population growth,
demographers must consider the age structure of each country, as well as the prevalence of life-threatening diseases.
• If growing countries move toward the demographic transition, growth rate may level off or decrease.
Future Population GrowthFuture Population Growth
Future Population GrowthFuture Population Growth• Ecologists suggest that if growth does
not slow down, there could be serious damage to the environment and global economy.
• Economists assert that science, technology, and changes in society may control the negative impact of population growth.
• Ecologists suggest that if growth does not slow down, there could be serious damage to the environment and global economy.
• Economists assert that science, technology, and changes in society may control the negative impact of population growth.
Let’s Review 5-3Let’s Review 5-3
5-35-3
– The size of the human population began to increase exponentially after the• bubonic plague.• development of plowing and irrigation.• Industrial Revolution.• development of the first cities.
– The size of the human population began to increase exponentially after the• bubonic plague.• development of plowing and irrigation.• Industrial Revolution.• development of the first cities.
5-35-3
– Which of the following is NOT a potential limiting factor of human population growth? • famine• medicine• war• disease
– Which of the following is NOT a potential limiting factor of human population growth? • famine• medicine• war• disease
5-35-3
– After the demographic transition is complete, a population• grows rapidly.• grows slowly.• begins a period of rapid decline.• stays about the same size as time passes.
– After the demographic transition is complete, a population• grows rapidly.• grows slowly.• begins a period of rapid decline.• stays about the same size as time passes.
5-35-3
– An age-structure diagram shows a breakdown of a population by• location and age group.• age group and gender.• birthrate and death rate.• age group and emigration rate.
– An age-structure diagram shows a breakdown of a population by• location and age group.• age group and gender.• birthrate and death rate.• age group and emigration rate.
5-35-3
– Since the mid-1960s, the average annual growth rate of the human population has• remained about the same.• failed to show a consistent pattern.• increased.• decreased.
– Since the mid-1960s, the average annual growth rate of the human population has• remained about the same.• failed to show a consistent pattern.• increased.• decreased.
END OF SECTION 5.3
END OF SECTION 5.3