Sampling

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  • Sampling
    • Random
      • Large sample (2% of area)
        • allow for anomalies
      • Tape measures on 2 sides of the area. Randomly generated numbers form coordinates
    • Systematic
      • Investigating a specific pattern
      • Transect
        • Line transect
          • The organisms touching the string layer next to the transect are recorded
          • More accurate but more time consuming
        • Belt transect
          • Quadrats are placed at intervals and organisms in each quadrat is measured
          • Faster but not as representative
        • Data shown in a kite diagram - biotic = kite. abiotic = line
          • Biotic & abiotic measurements at each site
    • Abiotic factors
      • Measured digitally - quick, accurate, automatic
      • Measurments should be repeated and averaged
        • Measured over days months and years allows for daily & seasonal changes
    • Biotic factor
      • Quantitive measurements
        • Abundance
          • Number of the organisms using mark release recapture. Abundance /sampling area = density
        • Growth
          • Comparing growth/sizeof similar organisms in similar habitats
        • Biomass
          • Dry mass shows productivity and used to make pyramids of biomass. Organisms warmed to 80 degrees to remove water and weighed until the decrease in mass stops
    • Sampling animals
      • Mark-release-recapture
        • A sample is captured and marked in some way that will not cause harm or increase predation.
        • They are then given time to mix with the rest of the population before a second sample is captured without too much time for births, deaths or migration
        • Count the number captured and the number recaptured then calc. the population. 1st sample x second sample/ recaptures
    • Sampling plants
      • Quadrat, frame quadrat, frame quadrat with grid and point quadrat
        • Preliminary experiment with different sized quadrats to form a species-area graph and find the most effective size
      • Quantitive measurements of the abundance of plants.
        • Percentage cover - difficult to identify individuals. Estimate and most accurate with a grid quadrat
        • Species Frequency - number of quadrats or squares in a quadrat containing the species
    • Analysing samples
      • Stats test give a probability (P-value) which gives the probability the results are due to chance a low P value shows significance
      • if P = 0.05 any correlation is due to chance
        • Use the words chance and probability
      • Null hypothesis (no difference) >0.05 accept null hypothesis
      • Looking for a difference (bar chart)
        • Can use SD or SE and the mean, if error bars overlap theres no difference
      • Looking for correlation (scatter graph)
        • Correlation doesn not always mean causation, there could be a 3rd factor, a control is needed.
      • Using Qualitive (categoric) data (pie chart)
        • Frequencies are recorded are compared to an expected ratio
  • Sampling animals
    • Mark-release-recapture
      • A sample is captured and marked in some way that will not cause harm or increase predation.
      • They are then given time to mix with the rest of the population before a second sample is captured without too much time for births, deaths or migration
      • Count the number captured and the number recaptured then calc. the population. 1st sample x second sample/ recaptures
  • Analysing samples
    • Stats test give a probability (P-value) which gives the probability the results are due to chance a low P value shows significance
    • if P = 0.05 any correlation is due to chance
      • Use the words chance and probability
    • Null hypothesis (no difference) >0.05 accept null hypothesis
    • Looking for a difference (bar chart)
      • Can use SD or SE and the mean, if error bars overlap theres no difference
    • Looking for correlation (scatter graph)
      • Correlation doesn not always mean causation, there could be a 3rd factor, a control is needed.
    • Using Qualitive (categoric) data (pie chart)
      • Frequencies are recorded are compared to an expected ratio

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