Practical 12 - sampling

Question 1

when is random sampling appropriate

Answer 1

if wish to sample a non motile species over a large area

Question 2

when is systematic sampling appropriate

Answer 2

wish to sample a non- motile species along an environmental gradient (an abiotic factor can also be measured to determine if there’s a correlation between abiotic factor and distribution of species)

Question 3

method of random sampling to determine total pop size

Answer 3

1. divide a map of the area into a grid
2. select random coordinates - RNG
3. quadrant at each coordinate
4. large number of quadrants
5. measure abundance of plant species in each quadrant by counting invidious plants or percentage cover
6. calculate mean abundance
7. multiply mean abundance by size of quadrant and size of total area to estimate total population size.

Question 4

systematic sampling method to determine total population size

Answer 4

1. set up transect by placing tape measure in a straight line along gradient
2. place quadrants at regular intervals (belt)
3. measure abundance of plant species (or percentage cover)
4. measure abiotic factor at each sample point and record result
5. repeat w more transects along gradient
6. calculate mean abundance and mean abiotic factor.

Question 5

why percentage cover may be used rather than frequency to measure abundance of particular species

Answer 5

species is too small to count - is faster way bc u don’t have to count all individual organisms

Question 6

describe how you’ll discover mean percentage cover for species X

Answer 6

randomly determine quadrant positions (use a lot) then count square if it’s covered by more than half w species and devidebtotal percentage cover by number of quadrants to give mean percentage cover.

Question 7

limitation of systematic sampling to estimate population of species X in feild

Answer 7

• not appropriate unless environmental gradient, transects run in one direction in a feild they would need multiple directions

Question 8

interrupted belt transect

Answer 8

quadrants places at intervals along transect with space between quadrants

Question 9

2 factors to consider when determining size of quadrant used

Answer 9

size of species, size of area investigated

Question 10

why is a large sample size important

Answer 10

• reduces effect of anomalies; ensures sample is representative of population

Question 11

what test used to determine relationship between abundance and an environmental factor.

Answer 11

spearman’s rank correlation coefficient