Quantitative Ecology

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Quantitative Ecology
2013-03-15 17:06:50
Quantitative Ecology

PWS 551 Quantitative Ecology: A few personal notes for midterm
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  1. Wiegert’s Method?
    • Pick the quadrat size or shape that minimizes the product of relative cost and
    • relative variance
  2. What size quadrat?
    • want norm dist
    • min edge effect
    • different species different values per size quad
    • easy to read
    • cost-person min/quadrat
    • stat precision high
  3. Hendrick's assumptions?
    • 1)
    • Assumes that the slope of the line is between 0 and -1.

    • •This
    • is a very restrictive assumption, and if the slope is not within this range,
    • the method can not be used

    • 2)
    • Assumes that the amount of time to read a quadrat is directly proportional to
    • size (i.e. 2m2 is twice as costly as 1m2).
  4. What's different about Hedrick's Method?
    • Pointed
    • out that variance usually decreased with larger quadrat size.

    • The
    • log of variance will fall linearly with the log of the quadrat size.
  5. Two approaches for picking size and shape quadrate?
    Go to lit, do same as everyone else.

    Better, do pilot study
  6. Sampling design?
    Method of placement

    • Number of samples
    • ..also think about gear (2 practical components)
    • decided before hand
  7. Best sampling design..
    smallest possible...
    at lowest...
    • efficiency
    • statistical estimates
    • confidence intervals
    • cost
  8. To determine a sampling design...
    decide on...
    select a...
    • statistical pop
    • sampling/experimental units
    • sample and adopt a variety of sample plans
  9. Simple random sampling?
    2 things
    • N sampling unit pop
    • every one has equal chance

    note: sampling with replacement better
  10. Stratified random sampling?
    • divided in subpops that don't overlap
    • randomly sample within each sub pop
  11. Strata?
    • a subpop in a stratified random sample
    • together make up entire pop
  12. random versus simple random sampling?
    • random=every indiv has equal chance
    • simple random=every possible group has an equal chance
  13. Benefits of Stratification?
    get estimates of means and confidence intervals for each subpop

    sampling problems can be addressed at each level


    maybe more than one lab studying same..admin convenience
  14. Systematic sampling?
    regular or systematic placement of samples

    simple and even, hopefully objective
  15. problems with systematic sampling?
    • periodic variation, not common though in ecology
    • still good if looking for gradients, or if you need cheap and easy
  16. centric systematic sample?
    equal strata, sample in middle
  17. Adaptive sampling? Why?
    Take advantage of spatial pattern to get a better estimate of abundance.
  18. Multi-stage sampling?
    two or more levels of sample selection; 7 lakes primary, benthic areas of 10m2 is element
  19. Cover? how is it expressed?
    area of ground covered by plants, rock, litter, bare ground

  20. Four types of cover?
    basal, canopy, foliar, ground
  21. cover, indicator of 2 things...
    • ecological processes
    • (dominance)

    management--erosion etc
  22. cover is a good substitute for....
    biomass; too hard and too much disruption.
  23. Three general approaches to measuring cover?
    Points, lines, plots/quadrats
  24. 3 Spatial patterns in nature?
    • Aggregated (clumped)
    • Uniform (regular or spaced)
    • Random
  25. poisson distributions resemble what kind of habitat distribution?
  26. Negative k binomial distributions are like what in nature?
    synonymous with aggregation
  27. 3 measures from Line Transect Sampling?
    • sighting distance
    • sighting angle
    • perpendicular distance
  28. Problems with Line transect sampling?
    • detectability falls with distance
    • undercount bias
  29. Detection function?
    estimate the zone of detectability, falls with distance
  30. distance methods, 2 general approaches?
    • random organism to nearest neighbor
    • random point to nearest organism
    • (object to object, or point to object)
  31. problems with object to object and point to object approach in distance methods?
    hard to pick a random organism

    point to organism is biased towards isolated individuals
  32. distance methods for plants?
    • nearest neighbor
    • point-centered quarter
    • nearest individual
    • random pairs

    there's more