P p population growths #4(1)
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P p population growths #4(1)






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P p population growths #4(1) P p population growths #4(1) Presentation Transcript

  • 4 Important characteristics ofPopulations• 1. GEOGRAPHICAL DISTRIBUTION – Area that is inhabited by a population • Varies in size from a few cm3 (bacteria) to millions of square kilometers
  • 2. Density of Area• # of individuals per unit area• Ex: desert cactus = low density• Cactus brush = high density
  • Partner activity: Density & GrowthRate• Density formula = # of indiv/area• 1. What is the density of 150 bullfrogs in a pond that covers an area of 3 sq. km?50 bullfrogs/sq. km
  • Growth Rate • Pf - Pi = Growth Rate **can be a neg. ∆Time number 1. In 1940, 4,800 sea otters were counted in a field study off the coast of Monterey, Calif. The field study continued until 1945 when scientists counted only 2,200 sea otters. What was the growth rate of sea otters? 2. -520 sea otters/year
  • More Problems• In the Fall of 2000, there were 1857 students at RAHS. This fall in 2008 the student count was 2,164. Growth rate?• 38 students/year
  • 3. Growth Rate (factors that affectpopulations• 1. Number of births (natality)• 2. Number of deaths (mortality)
  • 4. # of members that enter or leave the population• Immigration = movement of individuals into an area• Emigration = movement of individuals out of an area
  • Limiting Factors (affectingPopulations Growth) • Competition for • water • shelter • food • Predation • Parasitism & disease • Drought & climate change • Human disturbances
  • More Later
  • Graphs that represent Growth Rates
  • Exponential Growth (J- curve)EXPONENTIAL PHASE LAG PHASE
  • Exponential Growth• Occurs when a population reproduces at a constant rate.• At 1st, growth is slow• Under ideal conditions with unlimited resources, pop. will grow exponentially
  • • Example: bacteriaPartner Activity – Within 20 min. bacteria will divide & reproduce asexually – If an area starts with 2 bacteria cells on it, how many bacteria will have grown in 3 hours? ANSWER = 1024
  • Logistic Growth (S-curve)
  • Logistic Growth• As a resource becomes less available, populations slows or stops CARRYING CAPACITY EXPONENTIAL PHASE STABILIZATION PHASELAG PHASE
  • Predator-Prey Graph
  • Predator-prey Graph• The best known mechanism of pop.control• Pattern can repeat indefinitely
  • Extinction Graph
  • Extinction• Usually occurs: – After a catastrophic disaster • Asteroid impacts(?) • Fire • flood
  • Terms to Know• Carrying capacity - the largest # of indiv. That an environment can support. STABILIZATION PHASE EXPONENTIAL PHASE
  • • Stabilization phase – population has meet its carrying capacity and population growth levels off
  • • Exponential growth – a population that reproduces at a constant rate