Population Ecology Intro
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Population Ecology Intro



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Population Ecology Intro Population Ecology Intro Presentation Transcript

  • Population Ecology
  • What is population?
    • Group of individuals of the same species that live in the same area
  • Does population change?
    • Sea otters, kelp, and sea urchins
    • Kelp forests offer a habitat for sea otters
    • Sea urchins feed on kelp
    • Sea otters feed on sea urchins
  • Then come the hunters...
    • What do you think happens when sea otters are hunted?
      • Sea urchins increase or decrease?
      • Kelp forest increase or decrease?
    • Sea otters are then placed on the endangered species list
    • So now what happens to the population of sea otter?
      • Starts to increase
    • How does this affect the kelp and the sea urchins?
      • Sea urchins start to get eaten again=decrease in #
      • Kelp increases b/c less sea urchins to eat them
  • But now we have a new hunter….
  • What happens to the sea otter, kelp, and sea urchins?
  • What does this tell us about population?
    • Population changes
    • There are many factors that influence a population
      • Natural
      • Unnatural
    • Population density has a great impact on ecosystems
  • 3 important characteristics of Population
    • Geographic Distribution
    • Density
    • Growth Rate
    ***Population Age structure is also an important characteristic
  • Geographic Distribution
    • AKA Range
    • Describes an area inhabited by a population
    • Can vary
      • Few cubic centimeters
      • Kilometers of the ocean
  • Density
    • # of individuals per unit area
    • Low density
      • Cactus in desert
    • High density
      • Other desert plants and succulents
  • Math Time
    • Formula for calculating population density
    • Population density= Number of individuals
    • units area
    • Problem : Suppose there are 150 bullfrogs living in a pond that covers an area of 3 square kilometers. What is the density of the bullfrog population?
    • 50 bullfrogs per square kilometer
  • Growth Rate
    • Many factors affect growth rate
  • Sampling Techniques
    • How would we measure the population of a species?
    • Impractical to count each and every one
    • Variety of sampling techniques
      • Quadrants
      • Indirect counting
      • Mark-Recapture
  • Quadrants
    • Involves marking off specific area, boundary
    • Count specific species within the boundary
    • Repeat in several locations within desired ecosystem
    • Average the results to determine population density
    • More quadrants sampled=more accurate
  • Indirect Counting
    • Used for species that are too difficult to see or move around too quickly
    • Does not involve counting organisms themselves
      • Count nests, burrows, tracks
  • Mark-Recapture
    • Most common
    • Choose a study area
    • Trap/capture animals
    • Mark the captured animals and release back into habitat
      • Markings are not to disturb organism
    • After a period of time, recapture animals in the same study area
    • Count marked and unmarked organisms
  • How to Estimate Population from Mark-Recapture Method
    • Total population= (# in first capture) x (# in second capture)
    • number of marked animals RECAPTURED
  • Limits to Accuracy
    • Involve making assumptions about populations
      • Assumptions not valid=estimate not accurate
    • Quadrant
      • Assumption:
        • Organisms distributed evenly in study area
      • Problems
        • “ Clumps”
        • Quadrant with clump vs quadrant without clump
      • Minimize problem
        • Analyze how study population is distributed in order to choose appropriate quadrant size
    • Mark-Recapture
      • Assumption:
        • Both marked and unmarked animals have same chance of surviving and being recaptured in second trial
      • Problem
        • After being captured once, how do you think animals will behave?
        • Leads to overestimating population size
      • Minimize problem
        • Minimize effects of trapping on organisms
  • 3 Factors that affect population size
    • # of births
    • # of deaths
    • # of individuals that enter or leave population
    Population will increase or decrease depending on # of individuals added or removed
    • Have more births than deaths?
      • Population increases
    • Have more deaths than births?
      • Population decreases
    • Have equal amounts of births and deaths?
      • Population remains constant
    What happens to the population when we….
  • Immigration
    • “ im”= in
    • Migrate= to move from one place to another
    • Immigration is the individual movement into an area
    • Animals in search of mates and food in new areas
  • Emigration
    • “ E”  means ‘out’
    • Migrate  means to move from one place to another
    • Emigrate means individuals moving out of one place and into another
    • Young wolves and bears leaving as they mature
    • Shortage of food
  • Two types of growth
    • Exponential growth
      • Individuals reproduce at a constant rate
    • Logistic growth
      • Occurs when a populations growth slows or stops after a period of exponential growth
  • Exponential Growth
    • Occurs under ideal conditions with unlimited resources
    • Think about exponents in math….
    • Starts slowly then sky rockets to infinity
    • Our graph will look like a J
    • Bacteria
  • Lets look at bacteria…
    • Bacteria reproduce by splitting in half
    • Bacteria have a doubling time of 30 minutes
    • If you start will one bacterium, how many bacteria will there be after the first 30 minutes?
      • 2
    • After an hour?
      • 4
    • After an hour and a half?
      • 8
    • After two hours?
      • 16
    • After 15 hours?
      • Over a billion
  • Logistic Growth
    • As resources become less available, the growth of the population slows or stops
    • S-shape curve
    • What we usually see in nature
  • Carrying Capacity
    • The largest number of individuals that a given environment can support
    • The part of the logistic graph after the exponential growth…the flattening out
    • The point at which this flat line reaches the y-axis is the size of the population when the growth rate reaches zero
    • This doesn’t mean the population stops growing
    • Many factors slow the growth of plants and animals…