1. National 5 Biology Unit 3 – Life on Earth
Section 15 – Distribution of Organisms

2. Section 3. 15 – Distribution of Organisms Pupils should be able to:
Describe biotic factors such as competition for resources, disease, food availability and grazing.
Describe abiotic factors such as light intensity, moisture, pH and temperature.
Measure abiotic factors such as light intensity, soil moisture, pH and temperature.
Describe the sources of error for sampling abiotic factors
Sample biotic factors using techniques such as quadrats and pitfall traps.
Describe the limitations and sources of error for sampling biotic factors
Use and construct pair-statement keys to identify organisms
Describe the effect of biotic and abiotic factors on biodiversity and the distribution of organisms.
Evaluate and explain how indicator species indicate pollution levels by their presence or absence.
By the end of this section you should be able to:

3. Biotic Splat Abiotic Splat
Draw a Biotic and Abiotic splat on a piece of paper then try and match up the statements to the correct splat

4. competition
soil moisture
nitrate
content of soil
predation
carbon dioxide
level
temperature
availability
of food
oxygen
concentration
grazing
rainfall
air humidity
river flow
speed
phosphate
concentration
wind speed
build up of
organic waste pH
disease
light intensity
parasitism

5. Abiotic Splat Biotic Splat
river flow
speed pH
Biotic Splat
nitrate
content of soil
disease
competition
oxygen
concentration
predation
temperature
parasitism
grazing
rainfall
soil moisture
availability
of food
carbon dioxide
level
build up of
organic waste
light intensity
phosphate
concentration
wind speed
air humidity

6. Competition for Resources
Competition exists between living things that live ___________ ____________. Competition will occur if something is in short _______________. Competition can be between animals or plants of the same species or can be between _____________ or _________________ of ___________________ species.
close
together
supply
plants
animals
different
Battle at Kruger National Park -

7. Competition in Plants
Remember that plants make their own food using photosynthesis, so they do not compete for food. Here are some of the things that plants do compete for:
Light
Water
Space
Nutrients
You might get to set up an experiment to investigate competition in cress seeds.

8. Competition in Animals
Habitats have limited resources that are needed by living organisms. Organisms must compete with others in order to get enough of these resources to survive.
Animals will compete for:
Food
Water
Space
A mate to reproduce
Shelter

9. What is a Biotic factor? Competition for food Disease
A 'biotic factor' is any living component that affects another organism.
A biotic factor is any activity of a living organism that affects another living organism within its environment. Biotic factors within a community can affect the populations of organisms but are also essential to the balance of life within the ecosystem.
Competition for food
Disease
Predator/Prey relationships
Grazing

10. Competition for Food
A red squirrel and a grey squirrel living in the same habitat will compete for the same food source.

11. Grazing
Grazing is a method of feeding in which a herbivore feeds on plants such as grasses, or other multicellular organisms such as algae.

12. Which grassland looks to have the highest species diversity?
Grazing can also have a major effect on biodiversity.
Grazing is the eating of plants by herbivores.
This grassland is cut twice per year mimicking the effect of moderate grazing by herbivores.
This grassland has neither been grazed nor cut for at least a year.
Which grassland looks to have the
highest species diversity?
Why?

13. Affects of Grazing on Biodiversity
Low - small number of vigorous species dominate, reducing biodiversity.
Medium/High – gives other species a chance to compete, increasing biodiversity.
Very high - damages all species, reducing biodiversity.

14. Disease
The influenza outbreak of 1918 caused between 20 and 40 million human deaths, more people died of this than World War I.

15. Predation
Predator-prey relationships are examples of biotic factors. When the moose population is high on Isle Royale, the wolves have more food source from preying on the moose. This supports an increase in the wolf population.

16. Abiotic Factors What resources will an organism use in its ecosystem?
Light Intensity
Soil Moisture
pH Meter
Temperature

17. Light Intensity To use a light meter:
Direct sensor towards the light source
Read the correct scale

18. Soil Moisture To use a moisture meter:
Place the clean probe into the soil
Read the correct scale

19. pH To use a pH meter: Place the clean probe in the soil/water
Some plant species prefer particular pH ranges.
An increase in acidity in ponds can kill fish species
To use a pH meter:
Place the clean probe in the soil/water
Read the correct scale

20. Soil pH and Biodiversity
Different organisms do ‘best’ in different levels of soil pH.
Rock rose and thyme
Bee orchid
Sheep’s bit scabious
Land snails
alkaline soils
Ling heather
Sun dew
Butterwort
Rhododendron
Acid soils

21. Temperature To use a thermometer/ temperature probe:
Species are adapted to specific temperature ranges.
A change from the norm can kill species.
To use a thermometer/ temperature probe:
Do not cover sensor
Read the correct scale

22. Effect of Temperature on Biodiversity
Different organisms need different temperatures.

23. Location
Light Meter
Temperature
pH Meter
Soil Moisture

24. Sources of Error for Sampling Abiotic Factors
Sampling Technique
Possible Sources of Error
Ways to Minimise the Error
Light Intensity
Shading the light meter
May be affected by cloud cover
Stand back from meter
Take many samples so that the results are reliable
Soil Moisture
Not cleaning the probe in between readings
Moisture may be left on the probe
Wipe and dry the probe between samples and take many samples so that the results are reliable pH
Soil may be left on the probe
Temperature
Not waiting long enough for the thermometer to adjust
Allow probe to return to air temperature between readings

25. Sampling Techniques list
Quadrats
Sweep Net
Pit fall traps
Water Net
Tree Beating
Pooter
Tullgren Funnel

26. A quadrat is a square containing 25 smaller squares of equal size.
Quadrats
A quadrat is a square containing 25 smaller squares of equal size.
In order to sample plants (and slow moving animals) we can use a quadrat.
A quadrat marks off a small piece of ground of known area so that different plants present within this sample can be identified and counted or their area of cover estimated.
This sample gives us an idea of the number and kind of organism present in the whole area.

27. 2. To estimate the total number of a particular species of plant, the following calculation should be carried out.
10 m
10 m

28. Using a Quadrat
A. Measure the area of each quadrat.
The quadrats we use are 0.25m2 and sub-divided into 25 smaller squares each 100cm2.
The quadrat is placed randomly on the ground.
The number of small squares containing the plant we are interested in are counted.
This is called the abundance estimate.
Area= length x breadth
0.5m
= 0.5 x 0.5
=0.25 m2
B. Find out the average number of given plants in each quadrat
Total number in 5 quadrats
= 15
Average number in each quadrat
=15/5 = 3
In m2 there are 3 plants
In 1 m2 there are
3x4= 12 plants
(0.25 x 4 = 1m)

29. Quadrats Possible Sources of Error
Quadrat may be dropped in a position which gives good results e.g. not randomly sampled
Insufficient samples may be taken to be representative of the area.
Incorrect counting
Improvements
The quadrat should be dropped at random within the area to ensure it is representative of the area
To increase the reliability, take more samples (quadrats)

30. Belt/Line Transect Quadrat
A transect study can be used to show how distribution of species varies across a habitat

31. How to Carry out a Belt/Line Transect Study
A transect is a line across a habitat or part of a habitat.
It can be as simple as a string or rope placed in a line on the ground.
The number of organisms of each species can be observed and recorded at regular intervals along the transect.
You could use a quadrat or pitfall trap to monitor the living things along a transect line

32. Pitfall traps
What are pitfall traps used to sample?
Small invertebrate organisms living on soil surface.
Bury a container with drainage holes, level with the ground. Traps can be baited.
Protect the trap from rain by placing a piece of raised wood or slate above the trap.
Leave the trap overnight.
Replicate to give a representative sample of the area.

33. Pit Fall Traps Possible Sources of Error
Only traps ground fauna.
Easily disturbed
The numbers and types of animals may not be representative of the ecosystem as a whole.
Predation occurs - birds may eat trapped animals
Improvements
Incorrect identification
Predation occurs in the trap if left for too long.
Non-random sampling

34. A white tray or cloth can be used to collect the sample.
Tree Beating
Tree beating can be used to sample small invertebrates animals living in a tree on lower branches.
A white tray or cloth can be used to collect the sample.
Source of error:
Some organisms may miss the tray, drop of the edges or fly away.
Some animals may not be dislodged by beating

35. Tullgren Funnel
The Tullgren Funnel is an apparatus which helps to remove living organisms from leaf litter.

36. Leaf litter is placed in a filter funnel.
The funnel is then held over a bottle containing a mixture of alcohol and water.
There is a piece of gauze present to prevent soil entering the liquid.
Once the leaf litter has been placed in the funnel, the apparatus is put under a strong light for at least 2 weeks.
The soil dries out slowly and this encourages the living organisms to move downwards.
The living things can be examined using hand lenses or microscopes.
Possible Sources of Error Sieve mesh may be too fine and some animals fail to fall through. Soil sample may be too thick and may still contain many organisms at the end of the experiment.

37. Pooter Find a creature that you would like to examine more closely.
A pooter allows you to gently remove a small invertebrate from its habitat so that you can look at it more closely.
Find a creature that you would like to examine more closely.
Put the gauze covered tube into your mouth.
Place the other end of the pooter to within a few centimetres of the creature.
Gently suck in so that the creature is vacuumed into the straw and up against the gauze.

38. Sweep Net
A sweep net can be used to sample invertebrates in the air or in low lying bushes or grass.
To use a sweep net, move it back and forth gently through vegetation (long grass is ideal).
Try to swing the net in a figure-eight motion so that the open end of the net is always leading the way.
. One of the best ways to get creatures out of the net is to turn it inside out over a white cloth.

39. Water net Organisms and Ecosystems sampled
Organisms in freshwater stream or pond
Possible Sources of error:
Small animals may escape through the holes of the mesh
When looking for animals at the bottom of the pond, animals from the surface may have been caught from the water near the surface as the net passed through
Precautions:
Choose the net with finer mesh
Rotate the handle to close the opening of the net for the way up and down

40. Sources of Error for Biotic Sampling
Sampling Technique
Organisms used for
Possible sources of error
Ways to minimise the error
Quadrat
Estimate the number of plants or slow moving animals
Small sampling area.
Repeat the technique several times (5 or 10).
A plant might only be partly in the quadrat.
Decide on an in or out rule before starting.
Pitfall trap
Animals that are active on the soil surface and amongst leaf litter
Birds might eat the trapped animals.
Cover the trap with a lid.
Some animals might eat others.
Check traps regularly or put a preservative liquid in the trap (e.g. 50% ethanol).

41. Possible Sources of Error Ways to Minimise the Error
Sampling Technique
Organisms used for
Possible Sources of Error
Ways to Minimise the Error
Tullgren Funnel
Animals that live in the soil/leaf litter
Soil sample may be to thick
Spread a thin layer of soil over sieve
Sieve mesh may be too fine
Use mesh with larger holes
Sweep Nets
The net is moved through water to catch animals
Small animals may escape through holes
Chose a net with a finer mesh

42. Possible Sources of Error Ways to Minimise the Error
Sampling Technique
Organisms used for
Possible Sources of Error
Ways to Minimise the Error
Tree Beating
A stick is used to beat the branches of a tree, and animals drop onto the sheet below
Animals may miss the sheet or drop off the edge.
Take several samples by beating different branches
Use a large tray and quickly transfer to a bag
Some animals may not be dislodged
Use beaters of different lengths
Pooter
To trap small moving animals
Some animals may eat others
Take several samples.
Not enough samples taken
Use tubes with a wider diameter

43. A. Tree dwelling caterpillar
Quick Question
1. Match the organism to the sampling technique
A. Tree dwelling caterpillar
1. Pitfall Trap
B. Dandelion
2. Quadrat
C. Minnow (small fish)
3. Tree beating
D. Beetle
4. Water net
2. Can you suggest one precaution for each sampling technique?

44. Quick Question 1. Match the error and the precaution
1. Throw it randomly and repeatedly for reliable unbiased results
A. Overshadowing the meter
2. Make sure everyone is standing well away from the meter
B. Moisture from the last reading is still on the probe
C. Quadrat only thrown at parts of the field with daisies in it
3. Use a lid to hide the trap from birds
D. Birds have eaten all of the sample in a pitfall trap
4. Dry probe with tissue between readings

45. Identifying Organisms
It’s all very well counting organisms or collecting organisms.
Not all of them will be familiar to us.
In order to identify unfamiliar organisms, we would use a key.
There are different kinds of key.
We will use Paired statement keys.

46. Paired Statement Keys
Paired statement keys work in the same way as branching keys.
At each stage you are given a choice.
Make the appropriate choice and go to where you are asked to go.
Again, if the organism is present, you should end up with a name for it.

47. A Numbered Paired Statement Key
What’s this tree called ?
Needles go to 2
Broad Leaves go to 3
2. Leaves attached individually ……… Scots Pine
Leaves attached in bunches ……… Larch
3. Points on leaves ……… Holly
No Points on leaves ……… Oak

48. Are you a Dolphin?
Human
Porcupine
Panther
Dolphin
Panda
Perennial
Do you have spikes on you skin? ……….. YES, then you’re a porcupine
……….. NO – go to question 2
Do you have green leaves? ……….. YES, then you’re a perennial plant
……….. NO – go to question 3
Do you eat bamboo? ……….. YES, then you’re a panda
……….. NO – go to question 4
Do you have four legs? ……….. YES, then you’re a panther
……….. NO – go to question 5
Do you squeak and eat fish? ……….. YES, then you’re a dolphin
……….. NO – then you’re a human

49. 2. Wearing glasses ..….……..… Paul Not wearing glasses ... Go to No. 3
1. Male …………………... Go to No.2
Female ……………..… Go to No.4
2. Wearing glasses ..….……..… Paul
Not wearing glasses ... Go to No. 3
3. Dark hair ………………… Matthew
Fair hair ……………………... Chris
4. Long straight hair …………… Jane
Short curly hair …………….. Alison
Chris
Matthew
Jane
Alison
Paul

50. Air and Water Pollution
What is a Human Factor?
A ‘human factor' is any factor that is caused by humans.
Air and Water Pollution
Deforestation
Can be toxic to species, reducing biodiversity.
Desertification
The formation of deserts from the persistent degradation of dryland ecosystems by variations in climate and human activities.
Destroys habitats, reducing biodiversity.

51. Indicator species
A species whose presence, absence or abundance reflects a specific environmental condition, habitat or community.
Indicator species may:
Provide information on the overall health of an ecosystem.
Reflect a particular environmental condition, such as pollution.

52. Air pollution - Lichens
Lichens are formed from a symbiotic relationship between a fungus and an alga.
They often grow on exposed rocks and trees, and need to be efficient at absorbing water.
Air pollutants dissolved in rainwater, especially sulphur dioxide, can damage lichens and prevent them from growing.
Lichens are good indicators of air quality.
Lichens are formed from a symbiotic relationship between a fungus and an alga.
They often grow on exposed rocks and trees, and need to be efficient at absorbing water.
Air pollutants dissolved in rainwater, especially sulphur dioxide, can damage lichens and prevent them from growing.

53. Air pollution - Lichens
Shrubby and bushy lichens are usually the most sensitive to pollution and are often absent from polluted areas.
Air pollution - Lichens
Different lichens show different levels of tolerance to pollution.
Crusty lichens are usually more tolerant of pollution and can grow in more polluted areas.
Different lichens show different levels of tolerance to pollution.
Shrubby and bushy lichens are usually the most sensitive to pollution and are often absent from polluted areas.
Crusty lichens are usually more tolerant of pollution and can grow in more polluted areas.
By looking at the species present in a particular area, scientists can assess the level of air pollution.
By looking at the species present in a particular area, scientists can assess the level of air pollution.

54. Water pollution
Many aquatic animals can’t survive in polluted water, so their presence / absence can indicate the level of pollution in a water body.
Types of water pollution can include:
Nitrates (e.g. from fertilisers)
Acid rain
Heavy metals
Pesticides
Oil
Other chemicals
Many aquatic animals can’t survive in polluted water, so their presence / absence can indicate the level of pollution in a water body.
Types of water pollution can include:
Nitrates (e.g. from fertilisers)
Acid rain
Heavy metals
Pesticides
Oil
Other chemicals

55. Water Pollution - Invertebrates
Different invertebrate species are able to tolerate different levels of water pollution.
The composition of species within a study area can indicate the level of pollution.
Different invertebrate species are able to tolerate different levels of water pollution.
The composition of species within a study area can indicate the level of pollution.

56. Water Pollution - Invertebrates
Mayfly and stonefly larvae prefer clean water
Freshwater shrimp can tolerate low levels of pollution
The water louse can tolerate high levels of pollution
Examples include:
Mayfly and stonefly larvae prefer clean water
Freshwater shrimp can tolerate low levels of pollution
The water louse can tolerate high levels of pollution
Species such as the rat-tailed maggot and sludgeworm can tolerate very high levels of pollution
However, if the water is severely polluted, it may not be able to support any life at all.
Species such as the rat-tailed maggot and sludgeworm can tolerate very high levels of pollution

57. Indicator Species
The presence or absence of certain living organisms can also act as an indicator of the amount of pollution e.g. Air or water pollution.

58. Quick Quiz Name 4 abiotic factors
What sampling technique would you use to sample slow moving organisms and plants?
Name an error for the sampling technique in Q2 and state how you would correct this
Name 2 biotic factors
What is meant by the term ecosystem?