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Chapter 6 Population Biology

Chapter 6 Population Biology. 6.1 Dynamics Of Population Growth. Isle Royale moose wolves carrying capacity population balance. Species and Population. Organism Species: genetically similar organisms that reproduce Population: all members of a species in an area.

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Chapter 6 Population Biology

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  1. Chapter 6 Population Biology

  2. 6.1 Dynamics Of Population Growth • Isle Royale • moose • wolves • carrying capacity • population balance.

  3. Species and Population • Organism • Species: genetically similar organisms that reproduce • Population: all members of a species in an area

  4. Dynamics Of Population Growth • Exponential Growth - Growth at a constant rate of increase per unit time. (Geometric) • Arithmetic Growth - Growth at a constant amount per unit time.

  5. Population Growth • Growth rate = birth – death rates • Doubling time • Rule of 70 • Tdbl = 70/ann % incr.

  6. Feedback • Positive: Change leads to more change • More Offspring = More Future Parents • Exponential Growth • Positive = Mathematically, not Necessarily in terms of Desirability • Negative: Change opposes More Change • Rate of increase lessens • More Output = Less Competition for Product = Less Profit = Less Output

  7. Nothing Can Grow Forever • One cent @ 1% interest in 1 AD: • Would now be $4.9 million • One cent @ 2% interest in 1 AD: • Would now be $1,972 trillion • 328 million tons of Gold • Total Gold Production to data: 150,000 tons • Offsetting Growth • Money: Inflation, Devaluation, Default • Population: Epidemics, Famine, War

  8. Population Oscillations and Irruptive Growth • Irruptive or Malthusian growth • Overshoot • Dieback

  9. Malthusian Growth • Malthusian Growth (Irruptive Growth) - Population explosions followed by population crashes. • Thomas Malthus concluded unchecked populations tend to grow until they reach carrying capacity and are vulnerable to crashes. • To get land's fruit in quantityTakes jolts of labour ever more,Hence food will grow like one, two, three....While numbers grow like one, two, four....

  10. Growth to a Stable Population

  11. Logistic Growth • Logistic Growth - Growth rates regulated by internal and external factors until they come into equilibrium with environmental resources. • Growth rate slows as population approaches carrying capacity. • S-Shaped curve • Environmental Resistance - Any environmental factor that reduces population growth • Environmental Resistance = Negative Feedback

  12. J and S Curves • Initial Phase (J or Exponential) • No practical limits • Growth leads to more growth • Inflection Point: Opposing Forces Kick In • Later Phase (Top of the S Curve) • Growth has Costs • Costs Inhibit Growth • Final Outcomes • Stable Limit (Best Case) • Overshoot, Crash, Oscillations • Overshoot and Catastrophic Crash (Worst Case)

  13. Growth to a Stable Population • Logistic growth • Environmental resistance (Negative Feedback)

  14. 6.2 Strategies of Population Growth • Malthusian Strategies (r-selected species) • High Reproduction rates offset high mortality • Population limited by external factors • Logistic Strategies (K-selected species) • Low reproduction rates, usually don’t reach carrying capacity • intrinsically controlled growth

  15. r-selected species • Typically Small, Short Life Span • Insects • Rodents • Marine Invertebrates • Parasites • Annual Plants • Tribbles

  16. K-selected species • Low Reproduction Rates, Usually Don’t Reach Carrying Capacity, Longer Life Span, Bigger • Wolves • Elephants • Whales • Primates

  17. Growth Factors • Natality = new individuals • often related to Environmental Conditions • Mortality • Immigration • Emigration • r = (b – d) + (i – e) • Survivorship: number that survive • Life expectancy

  18. 6.3 Regulation of Population • Density-Independent • Affect natality or mortality independently of population density • Often abiotic (weather and climate, geologic hazards, fire…)

  19. Regulation of Population • Density-Dependent (competition) • Decrease natality or Increase mortality as population increases • Interspecific(Different Species): • predator-prey, parasites, symbiosis • Example: hare - lynx • Intraspecific (Same Species) • Territoriality • Stress and crowding (e.g. mouse)

  20. 6.4 Conservation Biology • Island biogeography describes isolated populations • Conservation genetics is important in survival of endangered species • Population viability analysis calculates chances of survival • Metapopulations connected

  21. Island Biogeography • Single islands always have fewer species than similar size areas on the mainland. • Because islands are isolated, it will be harder for species to immigrate to them, lowering the rate of immigration. • Limited resources on islands mean lower carrying capacity. • Applies to isolated habitats on land, also

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