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St. Joseph Bay and St. Andrews Jetties. Plot and Transect Density Sampling. Plot Sampling Ten 1m 2 quadrats Belt Transect Sampling Two 10m long transects Counted urchins in an area 0.5 m on either side of the transect = total of 10 m 2 sampled per transect. 1 m. 10 m.

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Plot and transect density sampling
Plot and Transect Density Sampling

  • Plot Sampling

    • Ten 1m2 quadrats

  • Belt Transect Sampling

    • Two 10m long transects

    • Counted urchins in an area 0.5 m on either side of the transect = total of 10 m2 sampled per transect

1 m

10 m


Plot and transect density calculations
Plot and Transect Density Calculations

  • Di = ni/A

    • Di = Density for species I

    • ni = Total number of individuals counted for species I

    • A = Total area sampled (will be 1 m2 for quadrats and 10 m2 for transects)

  • Calculate average density of urchins (#/m2 ) by quadrat sampling and by belt transect methods

  • Are they in close agreement?

    • If not, why do you think they are different?


Community structure trawling
Community Structure: Trawling

  • Graphical Examination

    • Species-Sample or Collectors Curve

    • Relative Abundance Curve

    • Lognormal Curve

  • Species Diversity Indices

    • Shannon-Weiner Index (H’)

    • Simpson Index (C)


Graphs collectors curve
Graphs: Collectors Curve

  • Cumulative number of species (Number of new species) is plotted against the number of samples taken

Curve has not become asymptotic. What does this suggest we need to do?


Graphs species abundance dominance density curve
Graphs: Species Abundance (Dominance Density) Curve

  • Rank the species based on number collected (1 = most abundant, 2 = next most abundant, etc.)

  • Plot abundance on logarithmic scale against the corresponding rank


Graphs lognormal curve
Graphs: Lognormal Curve

  • X-axis is divided into geometric abundance intervals (each interval width is a multiple of 2, so that the scale is the logarithm of the abundance to the base 2)

  • Plot number of species having certain abundances against the logarithmic abundance intervals


Species diversity indices
Species Diversity Indices

  • Shannon-Weiner Diversity Index (H’)

    • Combines two components of diversity

      • Number of species (higher number increases diversity)

      • Species evenness (evenness increases diversity)

    • The greater the value of H, the greater the diversity

  • Simpson Index (C)

    • Probability of picking two organisms at random that are different species

    • Gives less weight to more rare species and more weight to common species

    • Values range from 0 (low diversity) to 1-1/S (S = number of species)


Community structure assignment
Community Structure Assignment

  • Graphs

    • Collectors Curve

      • Seagrass trawls only

    • Species Abundance (Dominance Density) Curve

      • Seagrass combined data

    • Lognormal Curve

      • Seagrass combined data

  • Species Diversity Indices

    • Shannon-Weiner

      • Total collection for seagrass

    • Simpson

      • Total collection for seagrass

    • Answer questions on pg 34 (a and b)

    • Also, bonus question on pg 34


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