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Population Biology

Population Biology. Characteristics of Populations. Geographic Distribution- area inhabited by a population Density- number of individuals per unit area Ex. 150 bullfrogs per 3 km 2 What is the population density? Growth rate- populations may experience negative or positive growth.

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Population Biology

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  1. Population Biology

  2. Characteristics of Populations • Geographic Distribution- area inhabited by a population • Density- number of individuals per unit area Ex. 150 bullfrogs per 3 km2 • What is the population density? • Growth rate- populations may experience negative or positive growth

  3. Population Growth • Population Growth – an increase in the size of a population over time • Factors that affect population growth • # of Births • # of Deaths • # of individuals that enter or leave • Immigration vs. Emigration *Immigration- individuals move IN *Emigration- individuals move OUT orEXIT

  4. PopulationGrowth Can be negative or positive… • Suppose a penguin population was 1200 at the beginning of the year and 1600 at the end of the year… What was the total growth? • What if 450 adult penguins died during the year; what would the population’s growth be?

  5. Is not linear… Dollars earned Time in hours Population Growth

  6. Population size Time Population Growth • It is exponential- as a population gets larger, it also grows faster. • Individuals in a population reproducing @ a constant rate in “ideal” conditions… See pg. 121 Figure 5-3

  7. Population Growth • Cannot grow exponentially for very long • Has limits • Limiting factors- cause a population to stop increasing • Density dependent factors – depend on population size • have an increasing effect as the population increases

  8. Density Dependent Factors • Disease • Competition for resources-food, water, mates, territories, nesting sites • Predation • Stress

  9. 60 2400 50 2000 40 1600 1200 30 20 800 10 400 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 Moose Wolves How do increases and decreases in the moose population affect the wolf population?

  10. Density independent factors –affect all populations regardless of density • Temperature/Climate • Storms • Floods • Droughts

  11. Carrying Capacity The effects of Limiting Factors results in… carrying capacity- the number of individuals in the population that an environment can support

  12. Carrying capacity Number of Yeast Cells Time (hours) Growth Curve

  13. 1. Beginning Growth • Few starting members have offspring • The population increases slowly

  14. Carrying capacity Number of Yeast Cells Time (hours) Growth Curve Beginning Growth

  15. 2. Rapid Growth • Many organisms each reproducing • Fast increase • Exponential growth

  16. Carrying capacity Number of Yeast Cells Time (hours) Growth Curve Rapid Growth

  17. 3. Leveling Off • Becomes more difficult for each organism to meet its needs • Effect of density dependent factors increases • Growth slows

  18. Carrying capacity Number of Yeast Cells Time (hours) Growth Curve Leveling Off

  19. 4. Fluctuations • The number of organisms tends to remain near a level the environment can support • If the number of organisms goes too high: organisms die and the population drops • If the population is slightly low: births increase and the population rises

  20. Carrying capacity Number of Yeast Cells Time (hours) Growth Curve Fluctuations

  21. Carrying capacity Number of Yeast Cells Time (hours) 5. Carrying Capacity • The maximum number of organisms an environment can support

  22. TWO main Growth Curve Patterns 1. J-shape- organisms in unstable environments • Small body size • Reproduce rapidly • Short life span • Numbers die off under unfavorable conditions-few survivors reproduce rapidly when conditions improve • For example: bacteria, insects

  23. J-shape Growth Curve Pattern

  24. Growth Curve Patterns 2. S-shape- organisms in stable environments • Larger body size • Reproduce slower • Longer life span • Mature slower, live longer • For example: elephants, trees, humans

  25. Carrying capacity Number of Yeast Cells Time (hours) S-shape Growth Curve Pattern

  26. Human Population Growth Industrial Revolution begins Agriculture begins Bubonic plague Plowing and irrigation

  27. Human Population Growth • Birth Rate: the number of babies that were born in the past year • Death Rate: the number of people who have died in the past year. http://www.ux1.eiu.edu/~cfruf/popfac.htm

  28. Human Population Growth • Fertility Rate: The number of babies each woman is having during her fertile years. Total Fertility rates in the U.S. from 1917 to2000. http://www.ux1.eiu.edu/~cfruf/els_fertility_rates.htm

  29. Human Population Growth • Age Structure: can be used to determine how quickly a country or area is growing.

  30. U.S. Population Rwandan Population Males Females Males Females Age Distribution

  31. In which country…. • Are most individuals reproductive? • Are most individuals pre-reproductive? • Would the population be growing the fastest? • Would the population be growing the slowest? •   Populations that are not growing have about the same numbers of each age group.   

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