Populations

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Populations
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Populations

• Population- A group of organisms of the same
  species that live in a particular area.
• Three important characteristics of a population
  are its geographic distribution, density, and
  growth rate.

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POPULATIONS

• Population Growth- the change in the size of a
  population with time.
• Population Density- is the number of individuals
  per unit area.
• Geographic Density is how the population is
  distributed.

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POPULATION SIZE

• Three factors can affect population size.
• Number of births
• Number of deaths
• Number of organisms that enter or exit the
  population

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POPULATION SIZE

• Immigration- The movement of organisms into a
  population.
• Emigration- The movement of organisms out of a
  population.

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POPULATION 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.
• Often call J shaped curve.

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POPULATION GROWTH

• We do know that populations cannot grow
  exponentially for very long.
• What cause a population to slow down or even
  stop?
• RESOURCES! As resources become less available,
  the growth of a population slows or stops.

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POPULATION GROWTH

• Logistic Growth occurs when a population growth
  slows or stops following a period of exponential
  growth.

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Carrying Capacity

• Populations that illustrate logistic growth have
  reached their Carrying Capacity.
• CC- The number of organisms a given ecosystem can
  support.
• S-shaped curve

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Carrying Capacity
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Maintaining a Balance

• For a population to survive, a balance must exist
  between producers/consumers, predator/prey,
  growth and decay, water use and rainfalletc.

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Limiting Factors

• Limiting Factors- Any condition of the
  environment that limits the size of a population.
• Some can happen naturally and some are caused by
  humans.
• Ex Food, water, shelter and space availability,
  Predation, Climate, Disease, Pollution,
  Competition,.

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HUMAN IMPACT

• Humans have disrupted this balance through.
• Building of roads, industry, homes
• Pollution
• Hunting/poaching
• Global Warming, Excess CO2

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Predicting Carrying Capacity

• Because ecosystems change, carrying capacity is
  difficult to predict and calculate

• However, islands are the ideal place to study
  (clear boundaries)

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Rabbits in Australia

• no rabbits in native ecosystems of Australia
• introduced in 1859
• number increased rapidly ?plenty of vegetation
  no predators no competition
• disease and starvation caused the rabbit pop. to
  crash
• over time, vegetation recovered and rabbit pop.
  increased again
• continues to increase and decrease, but less
  dramatically

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Rabbits reduced Phillip Island to a wasteland.
Photos Department of the Environment and
Heritage
Recovery was spectacular after the rabbits were
eradicatedPhotos Department of the Environment
and Heritage
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• Reindeer near Alaska
• 25 reindeer introduced to one of Pribilof
  Islands near Alaska in 1911
• by 1938, herd had grown to 2,000
• reindeer ate mostly lichens, which grow back very
  slowly
• by 1950, only 8 reindeer alive on the island

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Predator/Prey

• This is an example of a predator/prey
  relationship.
• As one increases the other will as a result
  decrease..which in turns causes the other to
  decrease.
• A normal cycle

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Two Types of Population Regulation

• Cause of death may be density dependent or
  density independent

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Density Dependent Factors

• Density Dependent Factors have an increasing
  effect as populations increases
• These factors operate most strongly when a
  population is large and dense.

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Density Dependent Factors

• Competition
• Predation
• Parasitism
• Disease
• Crowding

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• Population is growing rapidly and there are
  limited resources, predation,
• or disease

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Density Independent Factors

• Density Independent Factors are factors that
  affect a population or cause death regardless of
  density.
• Severe weather, natural disasters and certain
  human activities like damming of rivers and
  deforestation.

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Human Population
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Human Population
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Human Population
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Human Population

• The human population has increased with time.
• For most of human existence life was hard and
  limiting factors kept the population in check!
• In fact only until recently.ONLY ½ of all
  children reached adulthood!

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Human Population

• About 500 years ago the human population began to
  increase.
• Growing Exponentially
• Industrial Revolution and Agriculture
  advancements are the reason for the drastic
  increase since the 1800s
• Currently at 7 Billion People
• The population trends differ depending on
  Developing and Developed Countries.

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DEMOGRAPHY

• Will our population continue to rise
  indefinitely? What is earth carrying capacity
  for humans?

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DEMOGRAPHY

• Some scientist once believed that war, famine,
  and disease would be our limiting factors.
• Do you agree?

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DEMOGRAPHY

• DEMOGRAPHY- The study of population.
• Demography examines the characteristics of human
  populations and attempts to explain how those
  populations will change over time!
• You can study charts of the age structure of a
  population and determine if it is growing or not.

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DEMOGRAPHY

• Over the last centruy population growth in the
  US, Japan and much of Europe has slowed
  dramatically.
• This hypothesis is referred to as DEMOGRAPHIC
  TRANSISITON- which is defined as a dramatic
  shift change between birth and death rates.

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Demographic Transition

• Throughout history, human societies have had both
  high birth rates and death rates.
• With advances in medicine, nutrition, and
  sanitation, etc more children survive and reach
  old age. These changes lower the death rate and
  demographic transition begins.
• For a brief time you have high birth rate but low
  death rates which causes your population to grow
  exponentially. (1770-1920 for the US)
• As societies modernize, (raise their standard of
  living, better education) the birth rate will
  begin to fall, the population growth will slow.
• The Demographic Transition is complete when
  birthrate falls to meet death rate and population
  growth stops.

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Demographic Transition

• Very few countries have actually completed DT
  most places are still growing exponentially.
• Much of the population growth today is
  contributed by only 10 countries .
• Guess the top 10 Countries!!!!
• http//www.mapsofworld.com/world-top-ten/world-top
  -ten-most-populated-countries-map.html This
  is NOT very accurate but still kind of neat!
• http//www.internetworldstats.com/stats8.htm

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Demographic Transition
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Demographic Transition

• The five stages of the demographic transition
  model
• Total population is low but it is balanced due to
  high birth rates and high death rates.
• Total population rises as death rates fall due to
  improvements in health care and sanitation. Birth
  rates remain high.
• Total population is still rising rapidly. The gap
  between birth and death rates narrows due to the
  availability of contraception and fewer children
  being needed to work - due to the mechanisation
  of farming. The natural increase is high.
• Total population is high, but it is balanced by a
  low birth rate and a low death rate. Birth
  control is widely available and there is a desire
  for smaller families.
• Total population is high but going into decline
  due to an ageing population. There is a continued
  desire for smaller families, with people opting
  to have children later in life

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Demographic Transition
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Developed Countries

• Higher Average Incomes
• Slower Population Growth
• Diverse Industrial Economies
• Stronger social support
• Uses a large of available resources
• Ex US, Canada, Japan, and countries of Western
  Europe

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Developing Countries

• Lower Average Incomes
• Simpler and agriculture-based economies
• Rapid Population Growth
• Uses small of available resources
• Ex Indonesia and
• countries in Africa.

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Total Population of the World by Decade,
19502050 (historical and projected)

Total Population of the World by Decade, 19502050 (historical and projected)
Year Total world population(mid-year figures) Ten-year growth rate ()
1950 2,556,000,053 18.9
1960 3,039,451,023 22.0
1970 3,706,618,163 20.2
1980 4,453,831,714 18.5
1990 5,278,639,789 15.2
2000 6,082,966,429 12.6
20101 6,848,932,929 10.7
20201 7,584,821,144 8.7
20301 8,246,619,341 7.3
20401 8,850,045,889 5.6
20501 9,346,399,468
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http//www.youtube.com/watch?vE8dkWQVFAoA
http//www.youtube.com/watch?vs-57ui-r6Qw
http//www.youtube.com/watch?viodJ0OOdgRg
http//www.youtube.com/watch?vVcSX4ytEfcE