Fieldwork techniques Flashcards
Why are samples taken?
most areas are too large to count every individual organism, so samples are used to draw conclusions about the whole area
quadrats
square frames used to take samples
How are quadrats used to sample an area?
- they are placed randomly in the area (can be done using a random number generator and coordinates)
- the number of study organisms is counted in each quadrat
- the number of organisms in the whole area is estimated using the equation:
mean number of organisms in one quadrat x (total area m[2] / area of one quadrat m[2])
transect
a straight line using something like a tape measure
What are belt transects used for?
to find the effect of abiotic and biotic factors on where organisms live/distribution
How are belt transects used?
quadrats (1 m x 1 m) are placed at regular intervals along a belt transect
changes in factors (temperature, light intensity, trampling) are recorded at each position as well as the number of study organisms
Examples of when a belt transect would be used (2)
when sampling from a pond to dry land
low tide on rocky shore to high tide
Why are changes in factors measured along a belt transect?
it makes it easier to link a change in distribution with a change in physical factor
Tem 1 m[2] quadrats were placed randomly on a school field that was 100 m by 200 m. The number of daises recorded in each quadrat was: 20, 6, 33, 0, 26, 21, 18, 7, 2 and 9.
Estimate the total number of daises on the field. [3]
mean number = total/number of quadrats = 14.2
estimated number = 14.2 x 20000/1 = 284000 daises
State when you would sample randomly with a quadrat. [1]
to estimate population number/size
Describe the situation in which you would choose to sample along a transect rather than sample randomly. [1]
when you want to study the effect of abiotic and biotic factors on where organisms live
to link a change in distribution with a change in a physical factor
