CP 15

Question 1

What is the independent variable in this

practical?

Answer 1

The sampling method such a using a frame or point quadrat or the quadrat size.

Question 2

What is dependent variable?

Answer 2

% Cover or Density of Species

Question 3

How is percentage cover calculated?

Answer 3

● Use a quadrat with squares.
● Count how many squares the required species is
present in. (Only count a square if more than half of
the square is covered).
● Divide this by the total number of squares available.
● Multiply by 100 to convert into a percentage (%)

Question 4

Outline the procedure to this practical.

Answer 4

1. Choose an area to take samples from. Use two tape measures to create a set of axes off which coordinates can be read.
2. Use a random number generator to generate 10 sets of random coordinates.
3. Place the quadrat at each of the coordinates, placing the bottom left corner on the coordinate every time. Start with the smaller quadrat.
4. Record the percentage cover for the chosen species.
5. Record the abundance of each species within the quadrat. This is used to work out density.
6. Record how many pins touch the chosen species. If it’s a frame quadrat record how many quadrat intersection points contain the chosen species underneath.
7. Repeat steps 3-6 with the bigger quadrat

Question 5

How can the results be used to determine if there is

a difference between the percentage cover or density for each sampling method?

Answer 5

Use a statistical test eg. t-test.

Question 6

EVALUATION

Answer 6

● it is impossible to completely control all the abiotic factors in the field
● % cover is purely an estimate
● may be difficult to count individual organisms if they are at very high frequency.
● only suitable for static/ very slow-moving organisms

Question 7

BIOLOGICAL EXPLANATION

Answer 7

A frame quadrat is a simple frame of a known area usually 50cm x 50cm. This can be used to make estimates of population density (number of individuals per unit area) or to estimate percentage cover (the proportion of the ground area covered by a species).

A point quadrat usually consists of a frame with holes through which long needles are lowered onto the ground below.

Percentage cover can be estimated from the proportion of the points that touch the species of concern. The intersections of a grid within a frame quadrat will be used in the same way.

Each intersection of the grid (where two wires cross) will be a ‘point’.

Question 8

Explain how the quadrat sampling should have been carried out.
(3)

Answer 8

 quadrats placed at random / sampling at random
(1)
 method of random number sampling eg random number generator(1)

 sampling done at same distance from
{traffic / road} (1)
 therefore removes bias / obtain running mean /
ensures valid data