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…
    • Factors Affecting Population Growth
      • Density-dependent Factors
        • Competition
        • Predation
        • Disease
        • Parasitism
        • Crowding and Stress
      • Density-Independent Factors
        • Weather /Natural disasters
        • Human activities
          • Fires
          • deforestation
    • -Involves more than one population -Rapid increase and decrease in populations