Chapter 5 Populations

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Chapter 5Populations

• 5-1
• How Populations Grow

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How Populations Grow

• Characteristics of Populations
• 4 important characteristics of a population
• Geographic distribution
• Density
• Growth rate
• Age structure

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Geographic Distribution

• Geographic distribution, or range, is a term that
  describes the area inhabited by a population.
• Ranges can very enormously in size

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Population Density

• Population density is the number of individuals
  per unit area.
• The population of saguaro cactus in the desert
  plant community has a low density, whereas other
  plants in that community have a relatively high
  density.

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Populations Growth

• Three factors can affect population size
• number of births
• the number of deaths
• the number of individuals that enter or leave the
  population.
• Simply put, a population will increase or
  decrease in size depending on how many
  individuals are added to it or removed from it

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Immigration Emigration

• Immigration
• the movement of individuals into an area, is
  another factor that can cause a population to
  grow.
• Emigration
• the movement of individuals out of an area, can
  cause a population to decrease in size.

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Word Origin

• Immigration is formed from the Latin prefix in-,
  meaning in, and migrare, meaning to move from
  one place to another.
• If the Latin prefix e- means out, then which of
  the following means migration out?
• A.) emigration
• B.) migration
• C.) Immigration

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Age Structure

• The number of males and females of each age a
  population contains.
• Age structure greatly effects reproduction

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Exponential Growth

• When the size of each generations offspring is
  larger than the generation before it this is
  exponential growth.
• If a population has abundant space and food, and
  is protected from predators and disease, then
  organisms in that population will multiply and
  the population size will increase.
• Under ideal conditions where resources with
  unlimited resources.

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Exponential Growth

• Exponential growth occurs when the individuals in
  a population reproduce at a constant rate.
• Under ideal conditions with unlimited resources,
  a population will grow exponentially.

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Checkpoint

• Which of the following is NOT a condition for a
  population to reach exponential growth?
• A.) presence of unlimited resources
• B.) Absence of predation and disease
• C.) movement of individuals out of the
  population

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Logistic Growth

• Logistic growth occurs when a population's growth
  slows or stops following a period of exponential
  growth.
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• As resources become less available, the growth of
  a population slows or stops. The general,
  S-shaped curve of this growth pattern, is called
  logistic growth.

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Carrying Capacity

• The maximum number of individuals of a
  particular species that a given environment can
  support.

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Review

• List four characteristics that are used to
  describe a population.
• What factors can change a population's size?
• What is the difference between exponential growth
  and logistic growth?

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Limits to Growth

• Limiting factor a factor that controls the
  growth of a population.
• Density dependent
• Density independent
• Limiting factors determine the carrying capacity
  of an environment for a species.

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Density- Dependent Factors

• Limit a population when the number of individuals
  reach a certain level
• Competition for food, water, space, sunlight,
  etc.
• Predation and Herbivory populations cycle up
  and down

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Wolf/Moose graph
Moose
Wolves
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Density- Dependent FactorsContinued

• Parasitism disease the denser the population
  the easier it spreads
• Stress from overcrowding can lower birth rates,
  higher death rates, can cause mothers to neglect
  young, even lead to emigration

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Density -Independent Factors

• Affect all populations in similar ways regardless
  of size and density
• Weather, natural disasters, seasonal change,
  human interventions (dams, logging, housing
  developments)

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• Populations usually decrease dramatically after
  such an event
• Can be permanent cause extinction

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Historical Overview

• For most of human existence, the population grew
  slowly because life was harsh. Food was hard to
  find. Predators and diseases were common and
  life-threatening.

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Historical Overview

• These limiting factors kept human death rates
  very high. Until fairly recently, only half the
  children in the world survived to adulthood.
• Because death rates were so high, families had
  many children, just to make sure that some would
  survive.

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Exponential Human Population Growth

• As civilization advanced, life became easier,
  and the human population began to grow more
  rapidly. That trend continued through the
  Industrial Revolution in the 1800s.

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The Predictions of Malthus

• This kind of exponential growth could not
  continue forever.
• Two centuries ago, English economist Thomas
  Malthus suggested that only war, famine, and
  disease could limit human population growth.
• Malthus thought that human populations would be
  regulated by competition (war), limiting
  resources (famine), parasitism (disease), and
  other density-dependent factors.
• Malthuss work was vitally important to the
  thinking of Charles Darwin.

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Patterns of Human 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.
• The scientific study of human populations is
  called demography. Demography examines
  characteristics of human populations and attempts
  to explain how those populations will change over
  time.

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The Demographic Transition

• To explain this shift, demographers hypothesize
  that these countries have completed the
  demographic transition, a dramatic change from
  high birthrates and death rates to low birthrates
  and death rates.

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The Demographic Transition

• Three stages
• Stage I, birthrates and death rates are high for
  most of history.

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The Demographic Transition

• In Stage II, advances in nutrition, sanitation,
  and medicine lead to lower death rates.
• Birthrates remain high for a time, so births
  greatly exceed deaths and the population
  increases exponentially.

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The Demographic Transition

• During Stage III, as the level of education and
  living standards rise, families have fewer
  children and the birthrate falls population
  growth slows.
• The demographic transition is complete when the
  birthrate meets the death rate, and population
  growth stops.

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The Demographic Transition

• So far, the United States, Japan, and Europe
  have completed the demographic transition.
• Parts of South America, Africa, and Asia are
  passing through Stage II.
• A large part of ongoing human population growth
  is happening in only ten countries, with India
  and China in the lead.

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The Demographic Transition

• Globally, human population is still growing
  rapidly, but the rate of growth is slowing down.
• Our J-shaped growth curve may be changing into a
  logistic growth curve.

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Age Structure and Population Growth

• To understand population growth in different
  countries, we turn to age-structure diagrams.
• These diagrams compare the age structure of the
  U.S. population with that of Guatemala.

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Age Structure and Population Growth

• In the United States, there are nearly equal
  numbers of people in each age group.
• This age structure predicts a slow but steady
  growth rate for the near future.

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Age Structure and Population Growth

• In Guatemala, on the other hand, there are many
  more young children than teenagers, and many more
  teenagers than adults.
• This age structure predicts a population that
  will double in about 30 years.

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Age diagram

• US slow but steady growth rate predicted
• Guatemala predicts population that will double
  in about 30 years.

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Future Population Growth

• To predict how the worlds human population will
  grow, demographers consider many factors,
  including the age structure of each country and
  the effects of diseases on death ratesespecially
  AIDS in Africa and parts of Asia.

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Future Population Growth

• Current data suggest that global human
  population will grow more slowly over the next 50
  years than it grew over the last 50 years.

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Future Population Growth

• 9 billion predicted by 2050
• What will stop/slow the growth?