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A population will increase or decrease in size depending on how many individuals ... natural disasters, seasonal cycles, damming rivers, and clear cutting forests ... – PowerPoint PPT presentation

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Title: Populations

Chapter Five Populations
Ava Bambico and Renata Costa
Characteristics of a Population
  • 3 characteristics that are used to describe a
  • Geographic distribution
  • Density
  • Growth rate
  • Community assemblage of different populations
    that live together in a defined area
  • Population group of individuals of the same
    species that live in the same area
  • Population Size
  • A population will increase or decrease in size
    depending on how many individuals are added to it
    or removed from it
  • Factors that can change a populations size
  • of births
  • of deaths
  • of individuals that enter or leave the

Population Growth
Carrying capacity the max of individuals the
environment can support Example the max
carrying capacity of the gym is about 765
people Limiting factor a factor that causes
population growth or decline Density-dependent
limiting factors limiting factor that depends on
population size Example competition, predation,
parasitism, and disease Density-independent
limiting factors limiting factor that affects
all populations in similar ways, regardless of
population size Example unusual weather,
natural disasters, seasonal cycles, damming
rivers, and clear cutting forests
How Populations Grow
  • Populations geographic distribution/range
    describes the area inhabited by a population
  • Population density number of individuals per
    unit area
  • Populations can
  • -grow rapidly
  • -decrease in size
  • -stay the same size from year to year
  • Changes in population
  • Immigration movement of individuals into an area
    population growth
  • Emigration movement of individuals out of an
    area population decline
  • Possible reasons for immigration animals in
    search of food and or mates

  • Competition
  • When populations become crowded, organisms
    compete with one another for food, water, space,
    sunlight, and other essentials.
  • The more individuals living in an area, the
    sooner they use up available resources
  • Can occur between members of different species
  • Predation
  • Interaction in which one organism captures and
    feeds on another organism
  • Predator-prey relationship
  • Mechanism of population control in which a
    population is regulated by predation

Exponential Growth
Exponential growth occurs when the individuals
in a population reproduce at a constant rate A
population will grow exponentially under ideal
conditions with unlimited resources
Logistic Growth
  • Logistic growth growth pattern in which a
    populations growth rate slows or stops following
    a period of exponential growth
  • Population growth will slow down when
  • the birthrate and death rate are the same
  • the rate of immigration is equal to the rate of

Human Population Growth
  • Human population tends to increase with time
  • Population grew slowly for the most of human
    existence because life was harsh, food was
    scarce, disease, etc.
  • About 500 years ago, population grew more rapidly
    because of
  • improved sanitation and health care reduction of
    death rate
  • industry made life easier and safer
  • the worlds food supply became more reliable

Patterns of Population Growth
The human population cant keep growing
exponentially forever because the earth and its
resources are limited Demography examines
characteristics of human population and attempts
to explain how those populations will change The
birth rates, death rates, and age structure of
populations help predict why some populations
grow faster than others
Patterns of Population Growth
Demographic transition the hypothesis that
explains why population growth has slowed down
dramatically in the U.S., Japan, and Europe The
levels of birthrates and death rates throughout
human societies have been equally high.Factors
such as advances in nutrition, sanitation, and
medicine, have lowered death rate . The
worldwide human population is still growing
exponentially.Most people live in countries that
have not yet completed the demographic
transition.Age-structure diagrams graph the
population of a country broken down by gender and
age group
Future Population Growth
  • Life threatening disease (AIDS, malaria,
    cholera), if rapidly growing countries move into
    demographic transition may cause the growth rate
    of the world population to level off or even slow
  • Many ecologists suggest that if the growth in
    human population does not slow down there will be
    serious damage to the environment and global

The End
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