required practical 12

Question 1

what is required practical 12?

Answer 1

Investigation into the effect of a named environmental factor on the distribution of a given species.

Question 2

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)

Answer 2

1. Divide two areas into grids / squares eg. place 2 tape measures at right angles
2. Generate a pair of coordinates using a random number generator (eg. on a calculator)
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 readings with a soil moisture meter

Question 3

Suggest why percentage cover may be used
rather than frequency. (1)

Answer 3

● Too difficult to count individual organisms /
individual organisms are too small to count

Question 4

Explain why random sampling is used. (1)

Answer 4

● To avoid sampling bias

Question 5

Explain the importance of a large sample size.
(2)

Answer 5

● Minimises the effect of anomalies
● Ensures sample is representative of the population

Question 6

Describe how you could decide the number of
quadrats that should be used in order to
collect representative data. (2)

Answer 6

● Calculate a running mean
● When enough quadrats, this shows little change
● Enough to carry out a statistical test

Question 7

Describe how you could investigate the effect of a factor on the distribution
of a species in a habitat (systematic sampling)

Answer 7

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

Question 8

Explain the limitations of using systematic
sampling to estimate the population of a
species in a field. (1)

Answer 8

● Not appropriate unless an environmental gradient
● Transects run in one direction, but to cover the entire field, they would need placing in multiple directions

Question 9

Which statistical test should be used to
determine the relationship between
abundance & an environmental factor? (1)

Answer 9

● Correlation coefficient eg. Spearman’s rank