Distribution of Organisms !!

What is an abiotic factor?

non-living factor

Examples of abiotic factors

Light intensity, moisture, pH and temperature

What is a biotic factor?

living factor

Examples of biotic factors

competition for resources, disease
,food availability, grazing and predation

What do you use to measure light intensity?

light meter

Sources of error while using a light meter?

- light sensitive panel shaded by user
- weather conditons affect readings

How to minimise error when using a light meter?

- Hold light meter at arms-length
- Take readings at the same time of day.

What do you use to measure Soil Ph?

Soil pH probe

Sources of error while using a Soil pH probe

Probe not cleaned between tests

How to minimise error while using a Soil pH probe

Always wipe probe between tests to avoid cross contamination

What do you use to measure moisture level?

Moisture probe

Sources of error while using a moisture probe

- There may be moisture on the probe from previous reading
- not enough samples are taken.

How to minimise error while using a moisture probe

-Wipe the probe with a paper towel.
- take a reapeat reading

What do you use to measure temperature?

thermometer

Sources of error while using a thermometer

- Probe not inserted deeply in soil
- Thermometer bulb held in user hand

How to minimise error while using a thermometer

- Push probe into soil enough
- Allow time for reading to be taken

What is a pitfall trap?

trap set in the soil to catch small animals

Limitations while using a pitfall trap

- Generally only suitable for small, surface crawling invertebrates
- Pitfall trap size
-Reliability limited by number of traps set

Possible sources of error while using a pitfall trap

-The numbers and types of animals may not be representative of the ecosystem as a whole
-Traps may not be placed randomly
-Inappropriate size of frap selected
-Too few traps used
-Birds may eat trapped animals
-Some animals may eat others

Ways to minimise error while using a pitfall trap

-Set up several traps
-Disguise the opening
-Check the traps regularly or put preservative such as 50% ethanol in the bottom of the traps
- cover to prevent rain entering trap

What is a quadrat?

a square frame enclosing a known area

Limitations while using a Quadrat

-Generally, only suitable for low growing, rooted plants
-Quadrat size
-Reliability limited by number of samples possible

Possible sources of error while using a Quadrat

-Quadrats may not be placed randomly
-Inappropriate size of quadrat selected
- Too few Quadrats used
- Plants misidentified

Ways to minimise error while using a Quadrat

Large number of quadrats used to improve reliability

Formula for calculating populations size

number in 1st sample x number in 2nd sample/ number in 2nd sample previously marked

What can abiotic factors affect?

If an abiotic factor increases or decreases, this impacts the size of populations in a community, which affects the population sizes of other organisms that depend on them.

What can biotic factors affect?

If a biotic factor changes, this impacts the size of populations in a community, which can have knock-on effects because of interdependence.

What is an indicator species?

Species that by their presence or absence indicate environmental quality / levels of pollution.