Ecological Sampling

1
Ecological Sampling

• What is a sample?
• A portion, piece, or segment that is
  representative of a whole
• Why do we sample?
• Because it is usually impossible to measure the
  whole
• e.g. survey of a countrys political preference
• e.g. number of barnacles at Race Rocks
• e.g. sizes and / or colours of sand grains from a
  beach

2
One big assumption

• That the sample is representative of the whole
• It is necessary to take enough samples so that an
  accurate representation is obtained
• It is important to avoid bias when sampling

3
RANDOM SAMPLING

• Often used when the area being studied is very
  large or when there is a limited amount of time
  available
• Random chosen by chance rather than according
  to a plan all outcomes are equally likely
• Samples are taken from different positions within
  a habitat and those positions are chosen randomly

4
How to sample randomly

• To sample individuals ???
• To sample a habitat ???
• Choose individuals or Place sampling units
  haphazardly
• This is rarely completely random however
• OR
• Assign numbers to the areas / individuals to be
  sampled
• Use a random number table to select which areas /
  individuals will be sampled
• http//www.randomizer.org/form.htm

5
SYSTEMATIC SAMPLING

• Samples are taken at fixed intervals, usually
  along a line (transect line - a line across an
  area to be sampled, marked by a tape measure)
• Transects are usually set up along an
  environmental gradient (e.g. high to low on a
  mountain)

6
Line transect method

• A measured line is laid across the area in the
  direction of the environmental gradient
• The species touching the line can be recorded
  along the whole length of the line (continuous
  sampling) or at specific points along the line
  (systematic sampling)

7
Belt transect method

• Similar to line transect but widens the sampling
  area
• Transect line is laid out
• Samples are taken by determining abundance or
  cover in an area that is a defined distance from
  the line
• Samples can be taken all the way along the line,
  at specific intervals or even randomly

8
STRATIFIED SAMPLING

• Used when there are small areas within a larger
  habitat that are clearly different
• Sampling is carried out randomly or
  systematically within each stratum
• This recognizes major differences within
  communities before sampling begins
• e.g. in the intertidal zone - high, middle, low
  zones

9
Quadrats

• Sampling unit consisting of a square frame
• Consistent size and shape of samples from
  different areas is essential
• Shape doesnt matter (can be rectangular or
  circular) as long as it is consistent and
  measurements are stated in write-up

10
Quadrat size

• Depends on area being sampled
• e.g. 1m x 1m quadrat used in forest to estimate
  tree abundance would be ridiculous
• Small quadrats are quicker to survey but yield
  less reliable data
• Large quadrats require more time and effort to
  survey but give more reliable data
• A balance between what is best and what is
  practical is necessary

11
Number of quadrats

• More quadrats is better but there are time and
  effort limitations
• How many is enough?
• Determine by plotting a graph of a given feature
  vs. number of quadrats

12
Your mission is

• Design a sampling protocol to answer the
  question
• Is there a correlation between the distribution
  and abundance of crab traps and birds from Pedder
  Bay to Race Rocks?