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Populations. Honors Biology – Chapter 5. What is a Population?. A group of the same species living in a given area It is populations or organisms that interact in ecosystems Example:. An Introduction – Sea Otters of the Pacific Northwest. Live in kelp forest community.

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Honors Biology – Chapter 5

what is a population
What is a Population?
  • A group of the same species living in a given area
  • It is populations or organisms that interact in ecosystems
  • Example:
an introduction sea otters of the pacific northwest1
An Introduction – Sea Otters of the Pacific Northwest
  • Sea urchins as food
    • Sea urchins eat kelp
  • Sea otters nearly eliminated due to hunting
  • Sea urchin populations rise
  • Kelp forests decline
  • Restoring balance: Sea otters declared endangered – protected from hunting
predator prey popluation relationships
Predator/Prey Popluation Relationships
  • Hare / Lynx
  • Hare population goes up
    • Lynx population goes up
      • Lots of food (hares) available
    • Causes hare population to go down
      • More lynx = more predation on hares
    • Causes lynx population to go down
      • Hare population decrease means less food for lynx and they die
4 characteristics of populations
4 Characteristics of Populations
  • Geographic distribution
    • Range
    • Area inhabited by a population
  • Density
    • Number of individuals per unit area
  • Growth rate
  • Age structure
population growth
Population Growth
  • 3 factors affect population size
    • Number of births
      • natality
    • Number of deaths
      • mortality
    • Number of individuals that enter or leave a population
      • Immigration - enter
      • Emigration - leave
population growth1
Population Growth
  • A population will increase or decrease in size depending on how many individuals are added to it or removed from it
  • Growth occurs if
    • More individuals are born than die
    • If birth rate equals death rate the population will stay near the same size
movement into or out of a population
Movement into or out of a population
  • May be caused by
    • Young animals mature and leave the area
    • Shortage of food in an area
exponential growth
Exponential Growth
  • Individuals in a population reproduce at a constant rate
    • Initially, growth is slow
    • Overtime the population becomes larger and large until it approaches an infinitely large size
    • Ideal conditions with unlimited resources required
  • Fastest rates of reproduction among living things
  • 20 minutes for population to double
  • Why don’t they take over the Earth?
    • NOT unlimited resources
logistic growth
Logistic Growth
  • Growth pattern that occurs when a population’s growth slows or stops following a period of exponential growth.
  • Things that slow a population’s growth
    • Natality (birth rate) decreases
    • Mortality (death rate) increases
    • Rate of immigration decreases
    • Rate of emigration increases
logistic growth1
Logistic Growth
  • Also, when birth and death rates are the same, the population growth will slow or even stop for a time
  • Even when a population stops “growing”, the population is still rising and falling somewhat – though the ups and downs average out to the same population size.
logistic growth curve
Logistic Growth Curve
  • Slow growth
  • Exponential growth
  • Growth levels off
  • Carrying Capacity
    • K
    • Dotted line
    • The maximum number of individuals that an environment can support
limits to growth
Limits to Growth
  • Limiting Factors
    • Factors that cause population growth to decrease
      • Competition
      • Predation
      • Parasitism
      • Drought
      • Human disturbance
there are two types of limiting factors
There are TWO types of limiting factors
  • Density Dependent
  • Density Independent
density dependent limiting factors
Density Dependent Limiting Factors
  • Depends on the size of a population
  • Usually greatest impact when the population is large and dense
  • Include
    • Competition
    • Predation
    • Parasitism
    • Disease
density independent limiting factors
Density Independent Limiting Factors
  • Affects all populations (large or small) in similar ways.
    • Unusual weather
    • Natural disasters
    • Human activities
      • Like Habitat Destruction
human population growth
Human Population Growth
  • Like other populations of organisms, the human population tends to increase with time.
human population growth curve
Human Population Growth Curve
  • Initially slow
    • Food scarce
    • Life harsh
  • 500 years ago
    • More rapid growth
      • Currently EXPONENTIAL
    • Why?
      • Agriculture and industry advances
        • Food supply increased
        • Improved sanitation
        • Medicine
  • The study of human populations
  • Examines human populations and tries to predict how they will change over time.
demographic transition
Demographic Transition
  • Population growth in some countries has slowed
    • U.S.
    • Japan
    • Much of Europe
  • Why?
    • Hypothesis: These countries have completed the “demographic transition
demographic transition1
Demographic Transition
  • A dramatic change in birth and death rates
  • What happens
    • Initially both birth and death rates high
    • Advances in nutrition, etc. lower death rate
    • Population increases rapidly
    • Societies modernize – increase education, etc.
    • Families have fewer children
    • Birthrate falls to meet the death rate
    • Population growth stops
populations that have not completed the demographic transition
Populations that have NOT completed the demographic transition
  • Most countries
    • India
    • China
age structure diagrams
Age Structure Diagrams
  • Shows how many people of different ages and genders are in a population
  • Useful in predicting future population growth
predicting future population growth
Predicting Future Population Growth
  • Factors to consider
    • Age structure of each country
    • Prevalence of life-threatening diseases
  • Predictions for 2050
    • 9 billion people on Earth
effects of human population growth
Effects of Human Population Growth
  • Some scientists suggest if human population growth rate does not become LESS than 0 (deaths outnumber births)
    • Serious damage to environment
    • Serious damage to global economy
  • Some economists say that technology advances and changes in societies can control negative impacts