Sampling techniques and the
measurement of abiotic and biotic factors
Previously we learnt about
abiotic factors that could affect
biodiversity
What is the definition of an abiotic factor?
A non-living factor in an ecosystem that can
effect organisms.
What are some abiotic factors in an ecosystem?
Light intensity, temperature, pH and soil moisture
Previously we learnt about
biotic factors that could affect
biodiversity
What is the definition of a biotic factor?
A living factor in an ecosystem that can
effect organisms.
What are some biotic factors in an ecosystem?
Predation, competition, diseases
Today we are learning about
• how abiotic factors can be measured
and errors avoided when measuring
them
• how to use a quadrat and pitfall traps
to assess the numbers of organisms in
an ecosystem
Abiotic factors include light intensity, temperature, pH
and soil moisture.
These are easy to measure using simple equipment.
Link the abiotic factor with the equipment used to
measure it?
Light intensity
moisture meter
Temperature
pH probe or meter
pH
thermometer
Soil moisture
light meter
Easy!
The teacher will now explain how to use the
Equipment for measuring abiotic factors,
how to avoid errors when using
the equipment and any limitations there might
be with the technique.
(Most of this is a re-cap of work done in S1 Science)
Light intensity
• Select the correct position if the meter has a
switch
• Put the meter in the
area to be measured
pointing the sensor
area at the source of
light
• Read the correct scale
and repeat a number of
times for the area.
The ERRORS to be
avoided include
correct switch position
and NOT shading the
sensor.
The limitation is that
light intensity changes
with day time and
cloud cover.
For which group of organisms might
light intensity be most important?
Why might light intensity be important to
these organisms?
pH and soil moisture
(Often measured by the same meter)
• Select the correct position if the meter has a
switch.
• Put the probe in the area
to be measured, covering
only the tip.
• Read the correct scale,
wipe the probe and
repeat a number of
times for the area.
The ERRORS to be
avoided include correct
switch position and
wiping the probe
after each measurement
is taken.
Not wiping the probe
will give a false
reading.
For which group or groups of organisms
might pH of their environment
or soil moisture be important?
Why might pH or soil moisture be
important to these organisms?
Temperature
• Put the thermometer
in the ground or water
and leave for the heat
to take effect.
• Read the scale and
carefully, wipe the
thermometer and
repeat a number of
times for the area.
For which group or groups of organisms
might the temperature of their
Environment be important?
Why might temperature be important to
these organisms?
The abundance of animals and plants
in an area can be estimated using a number
of sampling techniques including
quadrats and pitfall traps.
These techniques only give an estimate
representative sample and only if
enough replication is carried out.
Quadrats
These are a square frame sub-divided
into smaller squares.
They are often 0.5m by 0.5m divided into
25 smaller squares but can be much
smaller or bigger depending on the study
area.
They can be used in a random manner
or along a transect line.
Quadrats
These are a square frame sub-divided
into smaller squares.
Quadrats used
randomly to get an
overall abundance in
an area.
Quadrats used on a
transect line to help
understand the
changes in plants in a
specific area.
Quadrats
These give a representative sample
in a small area.
Enough samples must be taken in relation
to the size of area studied.
They can be used to generate results for
a larger area.
Pitfall traps
These are used to collect samples of small
organisms moving along the surface of the soil.
Dig a hole and place a pot in it, level with the
ground.
Put on a cover
(stone) and leave
overnight.
Check for organisms
the next day.
Pitfall traps
Only useful for small organisms.
Some organisms may eat others.
Organisms need to be identified
It gives a representative sample of the area.
What have you learned today?
Explain the meaning of abiotic factor?
What are 4 typical abiotic factors?
How can these factors be measured?
What errors can be made measuring them?
Explain the meaning of biotic factor?
What are 2 techniques used to sample organisms
in an area.