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Populations

Populations. Unit 2. Objectives. How Populations Grow Limits to Growth Human Population Growth. Characteristics of Populations. Three important characteristics of population: 1. Geographic Distribution: area inhabited by a population 2. Density: individuals per unit area

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Populations

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  1. Populations Unit 2

  2. Objectives • How Populations Grow • Limits to Growth • Human Population Growth

  3. Characteristics of Populations • Three important characteristics of population: • 1. Geographic Distribution: area inhabited by a population • 2. Density: individuals per unit area • 3. Growth rate: rate at which a population increases or decreases

  4. Population Growth • Three factors affecting population size: • Number of births • Number of deaths • Number of individuals that enter or leave the population

  5. Immigration vs. Emigration • Immigration: the movement of individuals into an area causing a rise in population • Emigration: the movement of individuals out of an area. • Examples?

  6. Exponential Growth • Follows the doubling rule: at a certain period in time, a population will double • If a particular bacteria had a doubling time of 20 minutes, how many cells will result at the end of one day? • Answer: 4,720,000,000,000,000,000,000

  7. Exponential Growth • Exponential growth occurs when the individuals in a population reproduce at a constant rate • Organisms reproduce at different rates

  8. Logistic Growth • As resources become less available, the population growth rate slows or stops • What are some factors that cause the growth rate to undergo logistic growth?

  9. Carrying Capacity • Carrying capacity is the largest number that the environment can support • This number is found at the level-off point of a logistic growth curve

  10. Limits to Growth

  11. Limiting Factors • Remember primary productivity? • Limiting nutrient is an example of a more general term: limiting factor • A limiting factor is any factor that causes population growth to decrease

  12. Density-Dependent Factors • A limiting factor that depends on population size • Include • Competition • Predation • Parasitism • Disease

  13. Density-Independent Factors • Affect all populations in similar ways regardless of population size • Includes: • Unusual weather • Human activity • Natural disasters • Seasonal Cycles

  14. Human Population Growth

  15. Historical Overview • Like any other populations, the size of the human population has increased over time • Currently growing at an exponential rate • High growth rate started 500 years ago • Why?

  16. Patterns of Population Growth • Thomas Malthus predicted that famine and disease would limit growth • Today, social and economic factors that influence human populations is called demography

  17. The Demographic Transition • Over the past century, growth rates in Japan, Europe, and the US have slowed • This trend is called a demographic transition

  18. The Demographic Transition • Has only been completed in a few countries • Population growth is attributed to 10 countries • Largest: • China • India

  19. Age Structure • Population Growth depends, in part, on the people of different ages in a population • Demographers predict future growth models with age-structure diagrams

  20. Age-Structure Diagram • Breaks down population by gender and age group

  21. Future Population Growth • Demographers predict that by 2050, the world growth rate will slow to .43% • Ecologists suggest that if the population does not slow down even more, permanent damage will be done to the planet

  22. World Population: 2000-2050

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