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Population ecology intro


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  • 1. Population Ecology
  • 2. What is population?
    Group of individuals of the same species that live in the same area
  • 3. Does population change?
    Sea otters, kelp, and sea urchins
  • 4. Kelp forests offer a habitat for sea otters
    Sea urchins feed on kelp
    Sea otters feed on sea urchins
  • 5. Then come the hunters...
  • 6. 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
  • 7. But now we have a new hunter….
  • 8. What happens to the sea otter, kelp, and sea urchins?
  • 9. What does this tell us about population?
    Population changes
    There are many factors that influence a population
    Population density has a great impact on ecosystems
  • 10. 3 importantcharacteristicsof Population
    Geographic Distribution
    Growth Rate
    Birthrate, death rate, individuals entering/leaving
    ***Population Age structure is also an important characteristic
  • 11. Geographic Distribution
    AKA Range
    Describes an area inhabited by a population
    Can vary
    Few cubic centimeters
    Kilometers of the ocean
  • 12.
  • 13.
  • 14. Density
    # of individuals per unit area
    Low density
    Cactus in desert
    High density
    Other desert plants and succulents
  • 15.
  • 16. 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
  • 17. Growth Rate
    Many factors affect growth rate
  • 18. Sampling Techniques
    How would we measure the population of a species?
    Impractical to count each and every one
    Variety of sampling techniques
    Indirect counting
  • 19. 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
  • 20. 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
  • 21. 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
  • 22. How to Estimate Population from Mark-Recapture Method
    Total population= (# in first capture) x (# in second capture)
    number of marked animals RECAPTURED
  • 23. Limits to Accuracy
    Involve making assumptions about populations
    Assumptions not valid=estimate not accurate
    Organisms distributed evenly in study area
    Quadrant with clump vs quadrant without clump
    Minimize problem
    Analyze how study population is distributed in order to choose appropriate quadrant size
    Both marked and unmarked animals have same chance of surviving and being recaptured in second trial
    After being captured once, how do you think animals will behave?
    Leads to overestimating population size
    Minimize problem
    Minimize effects of trapping on organisms
  • 24. 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
  • 25. 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….
  • 26.
  • 27. 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
  • 28.
  • 29.
  • 30.
  • 31.
  • 32. 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
  • 33. Two types of growth
    Exponential growth
    Individuals reproduce at a constant rate
    Population multiplies by constant FACTOR over constant time interval
    Logistic growth
    Occurs when a populations growth slows or stops after a period of exponential growth
    As population approaches carrying capacity, BR may decrease, DR may increase or both, until equal
  • 34. 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
  • 35. 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?
    After an hour?
    After an hour and a half?
    After two hours?
    After 15 hours?
    Over a billion
  • 36.
  • 37. Logistic Growth
    As resources become less available, the growth of the population slows or stops
    S-shape curve
    No net increase or decrease in population
    What we usually see in nature
  • 38.
  • 39. 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…
  • 40.
  • 41.
  • 42. Limiting Factor
    Condition that can restrict a population’s growth
    Could be:
    Availability of food
  • 43. Factors Affecting Population Growth
    • Density-dependent Factors
    • 44. Factor that limits population as population density increases
    • 45. Competition
    • 46. Predation
    • 47. Disease
    • 48. Parasitism
    • 49. Crowding and Stress
    • 50. Density-Independent Factors
    • 51. Factors that affect population but are unrelated to population density; affect population regardless of size
    • 52. Insects vulnerable to this
    • 53. Weather /Natural disasters
    • 54. Human activities
    • 55. Fires
    • 56. deforestation
  • Boom and Bust Growth Cycles
    Increase rapidly for a period of time followed by a sharp decrease in population for a brief period of time
    Still not completely understood
    Changes in food supply
    Stress from overcrowding
    Other organisms influence on population
  • 57. Boom-and Bust
    Population Cycles
    -Involves more than one population
    -Rapid increase and decrease in populations