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Populations

Populations. Chapter 19. Understanding Populations. Section 19.1. Definition:. A group of organisms of the same species living in the same place at one time. Thomas Malthus (1766-1834). Essay on the Principal of Population

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Populations

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  1. Populations Chapter 19

  2. Understanding Populations Section 19.1

  3. Definition: • A group of organisms of the same species living in the same place at one time

  4. Thomas Malthus (1766-1834) • Essay on the Principal of Population • In nature, plants and animals produce far more offspring than can survive • Man, too, is capable of overproducing if left unchecked • Famine and poverty are natural outcomes of overpopulation

  5. 3 Characteristics: 1. Size 2. Density 3. Dispersion

  6. Population Size • # of individuals in a given area • Difficult to measure • Estimates often taken

  7. Population Density • How crowded a population is • # of individuals per unit area • E.g.: 30 people/classroom

  8. Population Dispersion • Spatial distribution of individuals 1. Clumped 2. Even 3. Random

  9. Population Dynamics • Populations change over time due to: • Birth rates • Death (Mortality) rates • Life expectancy rates • Age Structure • Patterns of Mortality

  10. Age Structure • Distribution of individuals among different ages in a population

  11. Survivorship Curve Type I Type II % Survival Type III Age

  12. Patterns of Mortality • Survivorship Curves • Type I – death at old age • Type II – death at any age • Type III – death at young age

  13. Measuring Populations Section 19.2

  14. Population Growth Rate • # by which a population’s size changes over time • Depends upon: • 1. birth rate • 2. death rate • 3. emigration • 4. immigration

  15. Calculations • ADDS to population = birth & immigration • SUBTRACTS from population = death & emigration • ASSUME immigration = emigration • THEREFORE: birth rate – death rate = growth rate

  16. 2 Models of Growth • Exponential Model (J curve) 2. Logistic Model (S curve)

  17. Exponential Model • The larger the population gets, the faster it grows! • Birth & Death rates remain constant • Limitation: only exists under rare conditions • Doesn’t account for limiting factors that occur in nature

  18. Logistic Model • The exponential model accounting for the influence of limiting factors • Limiting Factor: condition that restricts growth of a population • Carrying capacity (K): # of individuals the environment can support of a long period of time • Fluctuates slightly

  19. Carrying Capacity

  20. 2 types of limiting factors • 1.Density-independent factors • Abiotic factors • Reduction of population by same proportion no matter what size it is • Ex) floods or extreme temp.

  21. 2. Density-dependent factors • Biotic factors • The larger the population, the larger the proportion of reduction. • Ex) disease or starvation

  22. Human Population Growth, 19.3

  23. History Lesson • Hunter-gatherer lifestyle: slow human growth because of high mortality rate • Agricultural revolution: human population growth because of an increase in the food supply • Industrial revolution: rapid human population growth because of decline in death rates

  24. Today’s Growth • Developed Countries: 20% of world’s population, low growth rates • Ex) USA, Japan, Germany, France, etc. • Developing Countries: 80% of world’s population, high growth rate • Ex) Central America, South America, Asia, Africa

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