A MAN LIVES ON THE TWELFTH FLOOR OF AN APARTMENT BUILDING. EVERY MORNING HE TAKES THE ELEVATOR DOWN

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• A MAN LIVES ON THE TWELFTH FLOOR OF AN APARTMENT
  BUILDING. EVERY MORNING HE TAKES THE ELEVATOR
  DOWN TO THE LOBBY AND LEAVES THE BUILDING. IN THE
  EVENING, HE GETS INTO THE ELEVATOR, AND, IF THERE
  IS SOMEONE ELSE IN THE ELEVATOR -- OR IF IT WAS
  RAINING THAT DAY -- HE GOES BACK TO HIS FLOOR
  DIRECTLY. OTHERWISE, HE GOES TO THE TENTH FLOOR
  AND WALKS UP TWO FLIGHTS OF STAIRS TO HIS
  APARTMENT.

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POPULATIONS

• Chapter 8-9

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What is a population?

• A group of organisms
• Must be the same species
• Must live in a given area

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What are some examples of populations?

• Cattle on a farm
• Deer in a forest

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2 Important Aspects of Populations

• Growth Rate
• Population Density

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GROWTH RATE
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POPULATION DENSITY
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Population Density
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What is Growth Rate?

• Change in population size
• Growth rate can be
• positive
• negative
• zero

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Why do populations grow?

• Positive growth is the result of larger birth
  rate than death rate.
• What would happen if the birth rate was lower
  than the death rate?
• A population will grow if more organisms are born
  in a given period of time than die during the
  same period.

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Types of Growth in Populations

• EXPONENTIAL
• GROWTH WITH LIMITS
• BOOM AND BUST

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EXPONENTIAL GROWTH

• Occurs when a population lives with ideal
  conditions.
• What are ideal conditions?
• As long as ideal conditions continue, the larger
  a population gets, the faster it grows. This
  type of growth is called exponential growth.

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Exponential Growth

• Example of Exponential Growth
• If a population consists of an organism living in
  ideal conditions when that organism reproduces
  there will be two, those two will reproduce and
  create two more for a total of 4, etc.

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PUZZLE

• If you put a coin in an empty bottle and insert a
  cork into the neck of the bottle, how could you
  remove the coin without taking the cork out or
  breaking the bottle?
• Why is it better to have round manhole covers
  than square ones?

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Types of Growth in Populations

• EXPONENTIAL
• GROWTH WITH LIMITS
• BOOM AND BUST

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Growth with Limits

• When a species lives under less than ideal
  conditions it will experience growth with limits.

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Growth with Limits
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Zero Population Growth

• Occurs when the birth rate is the same as the
  death rate.
• Population stays the same because the growth rate
  is ZERO.
• When a population is experiencing zero population
  growth it is said to be in the STEADY STATE.

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Carrying Capacity

• Carrying Capacity is the largest number of
  individuals that can survive over long periods of
  time in a given environment.
• The line represents the maximum amount of
  individuals that can live in the environment for
  a long period of time.

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Types of Growth in Populations

• EXPONENTIAL
• GROWTH WITH LIMITS
• BOOM AND BUST

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Boom and Bust

• Occurs when species reach a peak population size
  and then the population decreases quickly.

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Summary
Populations
Density
Growth Rate
Exponential
Growth with Limits
Boom and Bust
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POPULATION DENSITY

• Number of organisms in a given area.

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What determines Density?

• Density-Dependent Limiting Factors
• Density-Independent Limiting Factors

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Density-Dependent Limiting Factors

• Factors that limit populations that have a lot of
  individuals in a certain area.

Populations that have their growth rate
controlled by Density-Limiting Factors tend to
have stable populations
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Examples of Density-Dependent Limiting Factors

• Competition
• When populations become crowded they must compete
  for resources.
• Predation
• One species eats another species. (Food Chain)
• Parasitism
• Organism attaches to another organism and exists
  off the other organisms nutrients. (Ex. Fleas on
  a dog)
• Crowding
• Number of suitable territories is too small

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What determines Density?

• Density-Dependent Limiting Factors
• Density-Independent Limiting Factors

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Density-Independent Limiting Factors

• Factors that kill organisms regardless of how
  large a population is.
• Often these result in Boom and Bust growth rates.

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Examples of Density-Independent Limiting Factors

• Weather is the most important
• What kinds of weather could result in a bust of
  population?
• Other examples
• Toxic Waste spills
• Clearing forests
• Pesticides

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Summary
Populations
Growth Rates
Density
Density Dependent Limiting Factors
Density Independent Limiting Factors
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Reproductive Potential

• Reproductive potential is the maximum number of
  offspring that a given organism can produce.
• Some species have much higher reproductive
  potentials than others. Darwin calculated that it
  could take 750 years for a pair of elephants to
  produce 19 million descendants. While bacteria
  could produce that in a few days or weeks.

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• Reproducing earlier in life has the greatest
  effect on reproductive potential.
• Reproducing early shortens the generation time,
  or the average time it takes a member of the
  population to reach the age when it reproduces.

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Symbiosis

• The five major types of species interactions are
• Competition
• Predation
• Parasitism
• Mutualism
• Commensalism

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PUZZLE

• IN EACH OF THESE PUZZLES, A PROVERB IS WRITTEN
  WITH EXACTLY ONE LETTER OF EACH WORD REPLACED
  WITH ANOTHER. CAN YOU FIGURE OUT WHAT THE
  ORIGINAL PROVERB IS?
• I switch is dime raves mine.
• So nets if goof mews.
• Won't budge I took my ids covet.
• Won't pit oft pill gomorrow whet yon tan go
  toddy.
• Wetter mate that fever.

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HUMAN POPULATIONS
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• Demography is the study of the characteristics of
  populations, especially human populations.
• Developed countries have higher average incomes,
  slower population growth, diverse industrial
  economies, and stronger social support systems.
• Developing countries have lower average incomes,
  simple and agriculture-based economics, and rapid
  population growth.

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• The human population underwent exponential growth
  in the 1800s.
• Due to increased food production, improvements in
  hygiene (industrial and scientific revolution.)

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Age Structure Graphs

• Age structure is the classification of members of
  a population into groups according to age

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Survivorship

• Survivorship is the percentage of newborn
  individuals in a population that can be expected
  to survive to a given age.

• To predict survivorship, demographers study a
  group of people born at the same time and notes
  when each member of the group dies.

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• The results of these studies are then plotted on
  a graph and might look like one of the types of
  survivorship graphs below.

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• TYPE I Deaths occur in older organisms
• Typical of developed countries
• TYPE II Death is not dependent on age
• Fish, birds
• TYPE III Deaths occur in young organisms
• Any organism that produces many young because few
  survive

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Fertility Rate

• Fertility rate is the average number of births
  per woman aged 15 to 44.

• Replacement level is the average number of
  children parents must have in order to replace
  themselves.
• This number is slightly more than 2 because not
  all children born will survive and reproduce.

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• In 1972, the total fertility dropped below
  replacement level for the first time in US
  History.
• Fertility rates remained below replacement level
  for most of the 1990s, but recently has been
  growing partly because the children of the baby
  boom grew up and had children.

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Life Expectancy

• Life expectancy is the average length of time
  that an individual is expected to live.
• Life expectancy is most affected by infant
  mortality
• Expensive medical care is not needed to prevent
  infant deaths.
• Infant health is more affected by the parents
  access to education, food, fuel, and clean water.

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Immigration/Emigration

• Migration in general, is any movement of
  individuals or populations from one location to
  another.
• Movement into an area is immigration (In) and
  movement out of an area is emigration (Exit).
• The populations of many developed countries might
  be decreasing if not for immigration.

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Reducing the Population

• The factors most clearly related to a decline in
  birth rates are increasing education and economic
  independence for women.
• Educated women find that they do not need to bear
  as many children to ensure that some will
  survive. They may also learn family planning
  techniques.

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Reducing populations

• As countries modernize, parents are more likely
  to work away from home. If parents must pay for
  child care, children may become a financial
  burden rather than an asset.
• All of these reasons contribute to lower birth
  rates in both developed and developing countries.

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