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Population Ecology

Population Ecology. Elizabeth Petrie Jill Stittleburg Sherry Wiedman. Today’s objectives:. Define carrying capacity Describe how and why population growth rates change as the population approaches carrying capacity Discuss the “sixth extinction” and measurement of extinction rates

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Population Ecology

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  1. Population Ecology Elizabeth Petrie Jill Stittleburg Sherry Wiedman

  2. Today’s objectives: • Define carrying capacity • Describe how and why population growth rates change as the population approaches carrying capacity • Discuss the “sixth extinction” and measurement of extinction rates • Analyze human causes of extinction

  3. Changes in Population Size • What causes populations to change in size? • What are some factors that may limit population growth? • Is there a point at which the population cannot grow anymore? Why or why not?

  4. Population growth is a function of birth rate and death rate- If birth rate > death rate, population increases If death rate > birth rate, population decreases If birth rate = death rate, then the population stablizes

  5. Limiting Factors- • An environmental factor that prevents a population from increasing. Lack of : food water shelter space

  6. There are 2 types of limiting factors: • Density dependent factors • Density independent factors

  7. Density- dependent factors • Limiting factors that increase in intensity as the population increases in size. • Will reduce birth rates or increase death rates Ex. limited food supplies increased risk of infectious disease toxins due to increased waste levels

  8. Density-independent factors • Influence population rates regardless of their density Ex. weather events: drought, floods, extreme temperatures human interventions

  9. Carrying capacity • The maximum population that can be supported indefinitely in a given environment • Populations that are experiencing exponential growth eventually reach carrying capacity

  10. Fruit Fly Population Growth

  11. Population Growth • When conditions are good, a population can grow exponentially • The effects of declining resources gradually slow growth rate • Growth rate declines to zero as it approaches carrying capacity • If a population grows beyond the carrying capacity, a population crash may occur

  12. 14.1: The Sixth Extinction • Vocabulary • Extinction: complete loss of a species • Biodiversity: entire variety of living organisms • Endangered Species Act: law passed in 1973 with the purpose of protecting and encouraging the population growth of threatened and endangered species

  13. Endangered Species Act (ESA) • Written and passed because humans seemed to be triggering the rapid rate at which species were being lost • Ex: passenger pigeon, whooping crane, bald eagles, elephant seals • Critics of ESA say that saving all species is unrealistic goal because extinction is a natural process • The 10 million species living today represent only 1% of all species that have ever existed

  14. Measuring Extinction Rates • Earth’s history highlighted by 5 mass extinctions thus far • Mass extinction: period of a few thousand or few hundred years in which 50%-90% of living species lost From http://www.jkaneart.com/massextinctiongraph.htm

  15. Causes of Mass Extinction • First five thought to be caused by natural global changes: changes in sea level and climate fluctuations, changes in ocean and land forms—continental drift, asteroid impact • The sixth mass extinction (that scientists currently believe we are experiencing) is being caused by human activity

  16. Human causes of extinction: • Habitat Destruction • Habitat Fragmentation • Introduced Species • Overexploitation • Pollution

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