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Populations

Populations. Chapter 5. 4 important characteristics of a population. Geographic Range Density and Distribution Growth Rate Age Structure. Geographic Range. Describes an area inhabited by a population Can vary Few cubic centimeters Kilometers of the ocean. Density and Distribution.

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Populations

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  1. Populations Chapter 5

  2. 4 important characteristics of a population • Geographic Range • Density and Distribution • Growth Rate • Age Structure

  3. Geographic Range • Describes an area inhabited by a population • Can vary • Few cubic centimeters • Kilometers of the ocean

  4. Density and Distribution • Population density- the number of individuals per unit area.

  5. Formula for calculating population density • Population density= Number of individuals units area • Suppose there are 150 bullfrogs living in a pond that covers an area of 3 square kilometers. What is the density of the bullfrog population?

  6. 3 Factors that affect population size • # of births • # of deaths • # of individuals that enter or leave a population Population will increase or decrease depending on # of individuals added or removed

  7. What happens to the population when we… • Have more births than deaths? • Have more deaths than births? • Have equal amounts of births and deaths?

  8. Immigration • “im”= in • Migrate= to move from one place to another • Immigration is the individual movement into an area • Animal in search of mates and food in new areas

  9. Emigration • “E” = out • Migrate- to move from one place to another • Emigrate means individuals moving out of one place and into another • Young wolves and bears leaving as they mature • Shortage of food

  10. Two types of growth • Exponential growth • Individuals reproduce at a constant rate • Logistic growth • Occurs when a population growth slows or stops after a period of exponential growth

  11. Exponential Growth • Occurs under ideal conditions with unlimited resources • Think about exponents in math… • Starts slowly then sky rockets to infinity • Our graph would look like a J • Ex. Bacteria

  12. Logistic Growth • As resources become less available, the growth of the population slows or stops • S-shape curve • What we usually see in nature

  13. Carrying Capacity • The largest number of individuals that a given environment can support • The part of the logistic graph after the exponential growth… the flattening out • The point at which this flat line reaches the y-axis is the size of the population when the growth rate reaches zero • This doesn’t mean the population stops growing • Many factors slow the growth of plants and animals.

  14. Limiting Factors • Controls the growth of a population

  15. Density-Dependent Limiting Factors • Competition • Predation and Herbivory • Parasitism and Disease • Stress from Overcrowding

  16. Density- Independent Limiting Factors • Natural occurrences • Wildfires, drought, floods • It is difficult to say that a limiting factor act only in a density independent way.

  17. Human Population Growth • Exponential Growth • As life became easier the human population began to grow rapidly. • http://www.census.gov/main/www/popclock.html

  18. Thomas Malthus • Believed that human populations would be regulated by: • Competition (war) • Limiting resources (famine) • Parasitism (disease) • And Other density-dependent factors

  19. Demography • Examines the characteristics of human populations and attempts to explain how those populations will change over time.

  20. Age Structure and Population Growth

  21. Future Population Growth

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