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Understanding Population Growth: Patterns and Limits

Learn about population growth patterns, factors influencing growth, and limits to growth. Explore how populations impact each other. Discover the demographic transition in human populations.

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Understanding Population Growth: Patterns and Limits

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  1. Chapter 5POPULATIONS Lab Biology CP

  2. Red Crabs on Christmas Island in the Indian Ocean- What assumptions can you make about this population??? http://animal.discovery.com/videos/fooled-by-nature-christmas-island-crab-migration.html

  3. What problems does this population impose on other populations??

  4. Chapter 5:POPULATIONS • 5.1: How Populations Grow • 5.2: Limits to Growth • 5.3: Human Population Growth

  5. 5.1How Populations Grow

  6. What is a Population? • A population is a group of organisms of a single species that lives in a given area

  7. How do Ecologists Study Populations??? • 1.) Geographic Range • 2.) Density and Distribution • 3.) Growth Rate • 4.) Age Structure

  8. 1. Geographic Range • Geographic Range: • The area inhabitated by a population • Can vary in size • Small - Bacteria in a rotting pumpkin (<1 cubic meter) • Large - Cod in the Atlantic (hundreds of miles)

  9. 2. Density and Distribution • Population Density: • The number of individuals per unit area • Vary in densities • Distribution: • How individuals in a population are spaced out across the range of the population • 1.) Randomly • 2.) Uniformly • 3.) Clumps (most concentrated)

  10. 3 Types of Population Distribution

  11. 3. Growth Rate • Growth rate determines whether the size of a population increases, decreases, or stays the same. • Examples: • Zero growth rate: • When the population size stays the same • Positive growth rate: • Population increases • Negative growth rate: • Population decreases

  12. 4. Age Structure • Age structure: • The number of males and females of each age a population contains • WHY? • Because most plants and animals can’t reproduce until a certain age • Only females reproduce

  13. What factors affect population growth? • 1.)Birthrate • 2.) Death rate • 3.) Immigration • 4.) Emmigration Reasons for 3 & 4: • Food shortage • Overcrowding • Looking for mates

  14. Why does a population grow? • Has food • Has space • Protection from predators • Protection from disease • Has removal of waste products

  15. Exponential Growth • Exponential Growth: • The size of each generation of offspring will be larger than the generation before it • The larger the population gets, the faster it grows • Under idealconditions, a population will grow exponentially

  16. Rates of Growth • Reproduce Rapidly: • Bacteria • 1 day = 4,720,000,000,000,000,000 individual cells • Reproduce Slowly: • Elephants • 1 offspring every 2-4 years

  17. Logistic Growth • Logistic Growth: • Occurs when a population’s growth slows then stops, following a period of exponential growth • 3 Phases: • Phase 1 – Exponential Growth • Phase 2 – Growth slows down • Phase 3 – Growth stops • When birthrate and death rate are the same • When emigration equals immigration

  18. Carrying Capacity • Carrying Capacity: • The maximum number of individuals of a particular species that a particular environment can support

  19. 5.2Limits to Growth

  20. Limiting Factors • Limiting factors: • A factor that controls the growth of a population • Determine the carrying capacity of an environment for a species • Examples: • Competition • Predation • Parasitism • Disease • Natural disaster • Unusual weather

  21. How might each of these factors increase the death rate in a population?

  22. Density Dependent Limiting Factors • Operates strongly only when population density reaches a certain level • Examples: • 1. Competition • 2. Predation • 3. Herbivory • 4. Parasitism • 5. Disease • 6. Stress from overcrowding

  23. 1. Competition • Organisms compete for: • Food • Space • Water • sunlight

  24. 2 & 3. Predation and Herbivory • Predator-prey relationships • Cycle up and down over time • Herbivory effects • Herbivores are predators to plants • Cycle up and down • Humans as predators

  25. 4 & 5. Parasitism and Disease • Parasites make their hosts weak and may cause disease or death

  26. How does predation affect population growth?

  27. Density-Independent Limiting Factors • Affect all populations in similar ways, regardless of population size and density • Examples: • Hurricanes • Droughts • Floods • Wildfires

  28. Controlling Introduced Species • How to control runaway populations??? • Remove them • Herbicides • Problems: • Only temporary solution • Expensive

  29. 5.3Human Population Growth

  30. Has human population size changed over time? • Tends to INCREASE • Reasons: • Medication • Sanitation

  31. Patterns of Human Population Growth • Demography: • The scientific study of human populations • Predicted by: • Birthrates • Deathrates • Age structure

  32. The Demographic Transition • Demographic Transition: • Dramatic change from high birthrates and death rates to low rates • 3 stages

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