Required practical 12

• Describe how you could investigate the effect of an environmental factor on

  the distribution of a species in a habitat (random sampling in two areas)

  1. Divide two areas into grids / squares

  2. Generate a pair of coordinates using a random number generator

  3. Place a quadrat here and count number / frequency of [named species]

  ○ Standardise this eg. only count it if it is more than half in the quadrat

  4. Repeat a large number of times (10 or more) and calculate a mean per quadrat for both areas

  5. Measure environmental factor in each area eg. take soil moisture
• Suggest why percentage cover may be used

  rather than frequency. (1)

  ● Too difficult to count individual organisms /

  individual organisms are too small to count
• Explain why random sampling is used. (1)

  ● To avoid sampling bias
• Explain the importance of a large sample size.

  (2)

  ● Minimises the effect of anomalies

  ● Ensures sample is representative of the population
• Describe how you could decide the number of

  quadrats that should be used in order to

  collect representative data. (2)

  ● Calculate a running mean

  ● When enough quadrats, this shows little change

  ● Enough to carry out a statistical test
• Describe how you could investigate the effect of a factor on the distribution

  of a species in a habitat (systematic sampling)

  1. Place a transect line (tape measure) across an area with an environmental gradient eg. tree to full sun

  2. Place quadrats at regular intervals eg. 1m (until end of transect) and record the number of organisms of

  [named species] and [named environmental factor] eg. light intensity using a light meter

  3. Repeat in other parallel areas and calculate mean number of plants at each point along the transect
• Explain the limitations of using systematic

  sampling to estimate the population of a

  species in a field. (1)

  ● Not appropriate unless an environmental gradient

  ● Transects run in one direction, but to cover the entire

  field, they would need placing in multiple directions
• Which statistical test should be used to

  determine the relationship between

  abundance & an environmental factor? (1)

  ● Correlation coefficient eg. Spearman’s rank