Chapter 4: Populations

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Chapter 4 Populations

• Georgia Performance Standards
• Investigate the relationships among organisms,
  populations, communities, ecosystems, and biomes.

• EQ How would changes in populations affect the
  flow of energy and matter in the ecosystem?
• EQ How are populations regulated over time?
• EQ How does the growing human population
  threaten the biosphere?

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Warm-up

• A laboratory jar containing a population of
  beetle larvae (mealworms) has reached a stable
  population size. We decide to add twice as much
  food per day to the jar, but this turns out to
  have no effect on population size.
• What is the most likely explanation?

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Populations

• Defined by different geographical boundaries

• Important characteristics
• Density
• Geographical Distribution
• Growth Rate
• Age Structure

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What is POPULATION DENSITY?

• Immigration (im-uh-gray-shun), the movement of
  individuals into an area, can cause a population
  to grow.
• Emigration (em-uh-gray-shun), the movement of
  individuals out of a population, can cause a
  population to decrease in size.

• The number of individuals of a species per unit
  area or volume.
• Three factors can affect population size
• of births
• of deaths
• of individuals that enter or leave the
  population

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How do populations grow?

• Exponential Growth
• Under ideal conditions with unlimited resources,
  a population will grow exponentially

• The whole population multiplies by a constant
  factor during constant time intervals
• Organisms do not usually grow exponentially for
  very long.

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Exponential Growth

• Both of these hypothetical graphs show the
  characteristic J-shape of exponential population
  growth.

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Logistic Growth

•  As resources become less available, the growth
  of a population slows or stops Logistic growth
• Can follow a period of exponential growth

• S-shaped curve of this growth pattern
• birthratedeathrate immigration emigration

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Logistic Growth of Yeast Population
Carrying Capacity
Number of yeast cells
Time (hours)
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Carrying Capacity

• The number of individuals in a population that
  the environment can just maintain with no net
  increase or decrease

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Concept Map
Population Growth
can be
represented by
characterized by
characterized by
represented by
which cause a
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51 SummaryHow Populations Grow

• Three important characteristics of a population
  are
• geographic distribution
• density
• growth rate.
• Three factors affect population size of
  births
• deaths,
• of individuals that enter or leave the
  population.
• Under ideal conditions and unlimited resources, a
  population will continue to grow in a pattern
  called exponential growth. As resources are used
  up and population growth slows or stops, the
  population exhibits logistic growth.

• Vocabulary
• population density
• immigration
• emigration
• exponential growth
• logistic growth
• carrying capacity

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Checkpoint!!!

• Which of the following is NOT a condition for a
  population to reach exponential growth?
• presence of unlimited resources
• absence of predation and disease
• movement of individuals out of a population

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EQ How are populations regulated over time?
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Population Limiting Factors

• Environmental factors that restrict population
  growth.
• 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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Warm-up Population Limiting Factors

• 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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Density-dependent Factors

• Factors that depend on the population density
• Factors affect a greater percentage of
  individuals in a population as the number of
  individuals increases.
• Death rate increases and the birth rate decreases

• Limited food supply
• Competition
• Predation
• Parasitism
• Disease
• Buildup of poisonous wastes

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Density-independent Factors

• Limiting factors whose occurrence is not affected
  by population density
• Abiotic factors climate and weather or natural
  disasters and human activity
• Affect the same percentage of individuals
  regardless of the population size.

• Abiotic factors
• climate and weather
• natural disasters
• human activity
• Damming rivers
• Clear-cutting forests

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52 Summary Limits to Growth  

• Vocabulary
• limiting factor
• density-dependent limiting factor
• predator-prey relationship
• density-independent limiting factor

• Density-dependent limiting factors include
  competition, predation, parasitism, and disease.
• Unusual weather, natural disasters, seasonal
  cycles, and certain human activitiessuch as
  damming rivers and clear-cutting forestsare all
  examples of density-independent limiting factors.

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The Human Population

• EQ How does the growing human population
  threaten the biosphere?

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The size of the human population tends to
increase with time
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Demography

• The scientific study of human populations
• Birth rates
• Death rates
• Age structure of population

• All help to predict why some countries have high
  growth rates while other countries grow more
  slowly.

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Demographic Transition

• A dramatic change in birth and death rates
• The demographic transition is complete when the
  birthrate falls to meet the death rate, and
  population growth stops.

• Birthrates and death rates fall during the
  demographic transition. Initially, both rates are
  high (A). Then, the death rate drops while the
  birthrate remains high (B). Finally, the birth
  rate also decreases (C).

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Age-structure diagrams

• A population profile that can predict future
  growth.
• Shows the number of people in different age
  groups in the population

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Section 6-1
Human Activities
that have changed the biosphere include
may have once caused
often relies on the methods of the
have resulted in
which increased
Go to Section
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Threats to Biodiversity

• Human activity can reduce biodiversity by
  altering habitats (Habitat fragmentation),
  hunting species to extinction, introducing toxic
  compounds into food webs, and introducing foreign
  species (Invasive species) to new environments.

• Extinction occurs when a species disappears from
  all or part of its range.
• A species whose population size is declining in a
  way that places it in danger of extinction is
  called an endangered species.
• As the population of an endangered species
  declines, the species loses genetic diversity

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53 Summary Human Population Growth

• Like the populations of many other living
  organisms, the size of the human population tends
  to increase with time.
• The characteristics of populations, and the
  social and economic factors that affect them,
  explain why some countries have high population
  growth rates while populations of other countries
  grow slowly or not at all.

• Vocabulary
• demography
• demographic transition
• age-structure diagram