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Populations Chapter 5

Populations Chapter 5. Dr. Donna Howell Biology I Blacksburg High School. Characteristics of Populations. Three important characteristics of a population: Geographic distribution (where located) Density (how many per unit of area) Growth Rate (how fast population is growing).

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Populations Chapter 5

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  1. PopulationsChapter 5 Dr. Donna Howell Biology I Blacksburg High School

  2. Characteristics of Populations • Three important characteristics of a population: • Geographic distribution (where located) • Density (how many per unit of area) • Growth Rate (how fast population is growing)

  3. Population Size • Three factors influence population size: • Number of births • Number of deaths • Number of individuals that enter and leave a population Carsey Institute. Data from Census Bureau and National Center for Heath Statistics. The map above shows the number of years between 1966 and 2009 that a county had more deaths than births — when there was a natural decrease in population. The counties in dark red had a natural decrease in 30 or more years during that time. The blank counties had no years of a natural decrease.

  4. Population Size • Immigration – the movement of individuals into an area • Emmigration – the movement of individuals out of an area

  5. Exponential Growth • Exponential growth occurs when the individuals in a population reproduce at a constant rate. • Only occurs when population has unlimited resources. • Curve is “J” shaped.

  6. Carrying Capacity • Carrying capacity is the number of individuals that a given environment can support with its resources.

  7. Limiting Factors • Limiting factors are factors that cause a population’s growth to decrease. • Two kinds: • Density-dependent • Density-independent

  8. Density-Dependent Limiting Factor • A limiting factor that depends on population size. • Become limiting only when the population reaches a certain density. • Include: • Competition • Predation • Parasitism • Disease

  9. Competition • When populations become crowded, organisms compete for food, water, space, sunlight, and other essentials.

  10. Predation • When populations are controlled by the predator-prey relationship. • Example: snowshoe hare and lynx. As the population of hares increases, so does the population of lynxes. Eventually the lynxes will eat all the hares, and the hare population goes down in number.

  11. Parasitism and Disease • Diseases and parasites can sweep through a population and kill many. The more dense the population the faster the disease/parasite spreads. • Ex: Black Plague

  12. Density-Independent Limiting Factor • A limiting factor in which population size does not matter. • Some examples: • Natural disasters • Clear cutting of forests • Weather patterns (drought)

  13. Demography • Demography is the study of human populations. • Study things such as birth rate, death rate, and age structure (how many people of each age in a population) • Age-structure diagrams are useful in studying age structure.

  14. The End

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