3.7 RP

Question 1

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 1

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 2

Suggest why percentage cover may be used rather than frequency

Answer 2

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

Question 3

Explain why random sampling is used

Answer 3

● To avoid sampling bias

Question 4

Explain the importance of a large sample size

Answer 4

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

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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 7

Which statistical test should be used to determine the relationship between
abundance and an environmental factor?

Answer 7

● Correlation coefficient eg. Spearman’s rank

Question 8

Explain the limitations of using systematic sampling to estimate the population of a species in a field

Answer 8

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