# Sampling Techniques by a61N7e

VIEWS: 7 PAGES: 17

• pg 1
```									                                                   Sunday, November 04, 2012

Sampling Techniques
To know how to use different sampling techniques
 Organisms have special features which help them to survive in their
Sampling
 Biologists often want to find out what organisms are present in an
environment / what these organism do /where these organisms go
etc…

 Often it isn’t feasible to identify all the organisms present, so instead
samples can be taken

 Samples look at a small section, allowing us to predict what the whole
is like – e.g. would couldn’t feasibly measure the height of every blade
of grass, but we could look at a small sample grass and get an idea of
what all the rest may be like
Sampling Techniques
 How can we sample organisms / areas?

 Tagging – e.g. a few whales can be tagged and tracked, to give us an
idea of where their migration routes are
Sampling Techniques
 How can we sample organisms / areas?

 Pitfall traps – e.g. a small trap can be set to collect a range of
organisms within an area
Sampling Techniques
 How can we sample organisms / areas?

 Quadrat – e.g. a quadrat is thrown in an area, and the number of
organisms within the quadrant are counted to give an estimate for a
much larger area
 A quadrat is a 1m2 sampling square
 A quadrat is randomly placed in different locations, and the organisms
within the quadrat are counted so an average can be taken (the more
samples, the more accurate this method is)

If the field is 1000m2 then 1000 quadrats could fit (a quadrat is 1m2)
If the field is 5000m2 then 5000 quadratscould fit (a quadrat is 1m2)
Sampling Techniques
 Sampling is a good way to estimate population size – although is not
100% accurate, if done properly it can give good estimates and is very
time efficient!

 Your task in pairs is to sample how many daisies there are in 2
different parts of the field (open field & around tree)

 How can you sample to find if more daises grow in
the open field or around the trees?
Sampling Questions
 Sampling is a good way to estimate population size – although is not
100% accurate, if done properly it can give good estimates and is very
time efficient!

 Do More Daisies grow in the open or under trees?
   How many times will you have to do it?
   How are you going to sample your daisies?
   How will you choose which part to sample?
   How will you record your results?
   How long do you think it will take?
   What do you think you will find out?
   How will you make it safe?
Sampling Questions
 Using the quadrat you need to randomly throw it within the sample
area, and count the number of daisies within that area

 This needs to be repeated 3 times, and an average calculated for each
area of sampling – design a results table to collect your results…
Results
 Record your sampling results within the table
 Area 1 – open field
 Area 2 – around tree

Number of daises
Area
Sample 1        Sample 2         Sample 3   Sample Average

Open Field

Around
Trees
Findings
 Using your averages, work out the daisy population size in the open
field and around the trees

 Remember – the quadrant is 1m2 in area, and the field size is 100m2 in
the open field and 10m2 around trees

For example: -
 If your average daisies in the open field was 20, then a population
estimate would be 20 x 100 = 2000 daisies

 If your average daisies under the tree was 3, then a population
estimate would be 3 x 10 = 30 daisies
Analysis
 Can you suggest reasons why the population sizes are different?

 The daisies need a variety
of conditions to survive,
including light – around the
trees light is less abundant
than out in the open field,
so less daisies are able to
grow there

 There may also be less
nutrients / water available
allowing less daisies to
grow in this area
Moving
 Quadrats are usually used for plants, but they can also be used to
estimate some animal population sizes (as long as these only move a
little)!

```
To top