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AP Bio – Ecology Podcast 8

AP Bio – Ecology Podcast 8. Population Growth. How Populations Grow. Growth Birth (b) Immigration ( i ) Individuals that migrate into the population Decline Death (m) mortality Emigration (e) Individuals that leave the population Measured over a period of time.

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AP Bio – Ecology Podcast 8

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  1. AP Bio – Ecology Podcast 8 Population Growth

  2. How Populations Grow • Growth • Birth (b) • Immigration (i) • Individuals that migrate into the population • Decline • Death (m) • mortality • Emigration (e) • Individuals that leave the population • Measured over a period of time

  3. How Populations Grow – Two Models Ideal Conditions – Exponential Growth - No Resource Limitations Realistic Conditions – Logistic Growth - Resource Limitations

  4. Exponential Growth Model • The growth of a population continues indefinitely • Assumes no resource limitation • dN= riN • dt growth increasing at constant rate Change in #of Individuals (dN) Change in time (dt) r = how many offspring per individual in the poulation every pair has 4 offspring every pair has 3 offspring intrinsic rate= maximum rate of growth

  5. Factors that affect Population Growth • Abiotic factors • sunlight & temperature • precipitation / water • soil / nutrients • Biotic factors • other living organisms • prey (food) • competitors • predators, parasites, disease

  6. Factors that Limit Population Growth • Limiting Factors • Density Dependent • Density Independent

  7. Density Dependent Limiting Factors • The more organisms in the population, the more limiting these factors become… • Examples (mostly biotic): • competition: • food, • mates, • nesting sites • predators • parasites • pathogens

  8. Density Independent Limiting Factors • The number of organisms in the population really doesn’t matter • If a tornado hits, everybody gets killed… • Examples (mostly abiotic) • Sunlight • Temperature • Rainfall • tornado

  9. Carrying Capacity • Maximum number of individuals of a population that an environment can support. • K • Depends on resources available… • Limiting Factors

  10. Logistic Growth Model • Populations can’t grow exponentially forever • As N approaches K, rate of growth decreases no natural controls K =carryingcapacity effect of natural controls

  11. Populations Typically Oscillate Around K • Population cycles • predator – prey interactions • Boom and Bust K K

  12. Are there times when exponential growth does occur? • Characteristic of populations without limiting factors • Species introduced to a new environment (i.e. invasive) • Species rebounding from a catastrophe Whooping crane coming back from near extinction African elephant protected from hunting

  13. Other Factors Affecting Population Growth Rates • sex ratio • how many females vs. males? • generation time • at what age do females reproduce? • age structure - how females at reproductive age in cohort?

  14. Demography • Factors that affect growth & decline of populations • vital statistics & how they change over time Life table males females

  15. Age Structure Diagrams • Relative number of individuals of each age What do these data imply about population growth in these countries?

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