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Understanding Populations and Human Population Growth

This chapter explores the concept of populations, including population size, density, distribution, and dynamics. It also examines the factors influencing population growth and the impacts of human population growth on the environment.

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Understanding Populations and Human Population Growth

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  1. Chapter 20 POPULATIONS

  2. As the human population grows, the population of other species declines Population: a group of organisms that belong to the same species and live in a particular place at the same time 20.1 Understanding Populations

  3. Population Size • The actual population size can be difficult to measure • Individuals can be too abundant, too widespread, or too mobile to be easily counted

  4. When it isn’t possible to count every member of the population, a sample is taken From that sample, the population can be estimated Sampling a Population

  5. Population Density • Measures how crowded a population is • Expressed as the number of individuals per unit of area or volume • Estimates are calculated for the total land area

  6. The spatial distribution of individuals within a population Clumped: clustered together Even: separated by the same amount of space Random: no pattern Dispersion

  7. Clumped Distribution • Food or living space may be clumped • Social behavior (herds) • Flocking behavior

  8. Even Distribution • Social interactions • Colonial nesting behavior • V-pattern in flight (waterfowl migration)

  9. Random Distribution • Results from seed dispersal by wind or by birds • Example: forests or a field of wildflowers

  10. Birth rate: the number of births occurring over a certain period of time Death rate/mortality rate: the number of deaths over a period of time Life expectancy: how long an individual is expected to live (the average life span) Population Dynamics

  11. Age Structure • Shows the distribution of individuals in different age groups in a population • Populations with a higher percentage of younger individuals will tend to have rapid growth

  12. Survivorship curves: show the likelihood of survival at different ages throughout the life of an organism Type I, II, or III Patterns of Mortality

  13. Types of Survivorship Curves • Type I: the chance of dying is small until late in life • Type II: the chance of dying is the same regardless of age • Type III: the chance of dying while young is great

  14. 20.2 Measuring Populations Growth Rate: the amount by which a population changes size in a given amount of time Depends on birth, death, emigration and immigration Birth rate – death rate = growth rate

  15. Immigration: movement INTO a population Emigration: movement OUT OF a population Immigration vs. Emigration

  16. The Exponential Model • Describes a population that increases rapidly after only a few generations • The larger the population gets, the faster it grows • J-shaped curve • Will become limited by not enough food and too much wastes (limiting factors)

  17. The Logistic Model • Describes a population that becomes stable at the carrying capacity • Carrying capacity: the number of individuals the environment can support over a long period of time • S-shaped curve

  18. Density-independent factors: reduce a population regardless of the population size (weather, natural disasters, fire) Density-dependent factors: the higher the population, the more organisms that are affected (food, territory, nest sites) Population Regulation

  19. Population Fluctuation • Populations can fluctuate due to environmental changes • Example: population cycle of the snowshoe hare and the lynx

  20. Small populations are at risk of extinction Vulnerable to inbreeding, disease, environmental disturbances, etc. Inbred offspring have shorter life spans, decreased genetic variability, and are more susceptible to diseases Perils of Small Populations

  21. 20.3 Human Population Growth • Early human populations lived in small nomadic groups and obtained food by hunting and gathering • Had a high mortality rate, especially among infants and children

  22. 10,000 years ago, humans domesticated animals and cultivated plants Agriculture increased the available food supply Human population began to grow faster The Agricultural Revolution

  23. The Industrial Revolution • After the Middle Ages, 25% of the human population in Europe died due to the bubonic plague • The industrial revolution began around 1780 when there was a shift to using machinery and burning fossil fuels • Improvements in hygiene and in health care led to population growth

  24. Developed countries: modern, industrialized areas with better health care, longer life expectancies, but lower population growth Examples: U.S., Japan, Canada, Russia, Germany, Australia Includes only 20% of the world’s population, but uses 75% of all fossil fuels! Developed Countries

  25. Developing countries: poorer areas, lower life expectancy, but higher population growth Examples: Central America, South America, Mexico, Africa Includes 80% of the world’s population, but uses only 25% of the fossil fuels globally Developing Countries

  26. Human Population Explosion • By 2020, the human population could be as high as 12.5 billion • Will Earth be able to sustain that amount of people or will the human population reach its carrying capacity?

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