Significant ideas:

• The description and investigation of ecosystems allows for comparisons to be made between different ecosystems and for them to be monitored, modelled and evaluated over time, measuring both natural change and human impacts.

• Ecosystems can be better understood through the investigation and quantification of their components.

A major part of environmental systems is outside of the classroom and away from the books and computers. It is getting out into the environment and investigating and quantifying the ecosystems and the societies that live in them. Everything you study in this subject is about systems and the best way to understand them is to measure and quantify them to see how a change in one area may impact a very different aspect of the system. Facts and figures allow us to build models and make predictions.

Figure 1. Collecting data.

When studying ecosystems or societies it is important to narrow down your investigation to a small section of the system, otherwise there is too much data to be collected and that makes interpretation very difficult. When discussing your investigations use very specific examples of both ecosystems and societies.

Nothing in ESS is static; everything changes and that gives a wide range of potential investigations. You can look at different elements of an ecosystem and how they change in either time or space. What happens to temperature or light as you move through a forest? For example, what happens to the biodiversity of an ecosystem as it goes through succession? There is an endless list of questions to which you can find the possible answers through personal investigation. In doing this we can monitor ecosystems and develop models to predict how they may change in the future.

Figure 2. Changing light in a forest.

It is also possible to investigate the human element or societal aspect of ESS. How do human populations change with development? Which countries of the world have the largest ecological footprint?

The best investigations combine a study of the environment with the impact humans are having and what changes they are causing. If we investigate an ecosystem we can compare the before and after – what was it like before humans moved in and what is it like afterwards? It may be possible to predict what will happen if human action continues as it is. It may force society to evaluate its actions and the possible long-term outcome of them!

Figure 3. How many dead sharks does it take?

You are going to collect data following someone else's IA. Read the IA below and try to follow the instructions to collect data to answer the same question, test the same hypothesis and fill in the same data tables.

Afterwards: Reflect on the quality of the instructions. What could have been improved? Did the data collection allow you to answer the question?

Sampling

When studying an ecosystem it is a good idea to be very specific about the ecosystem and its location. "tropical rainforest" is not really adequate, "Bukit Timah Nature Reserve, managed tropical rainforest" is much better.

There are many factors that can be measured in an ecosystem:

• Biotic factors - e.g. abundance of organisms (density, percentage cover or frequency), identification of species, biomass, species richness and diversity.
• Abiotic factors - e.g. temperature, salinity, pH, light intensity or wind speed.

Factors can be measured:

• At a particular point in time.
• You can study the way they change over space.
• You can measure the way they change through time.

Sampling strategies

No matter what measurements you are taking you will usually have to take a sample. According to Investopedia sampling is "A process used in statistical analysis in which a predetermined number of observations will be taken from a larger population."

When investigating the plant diversity of two forest areas the most accurate method would be to count every single plant species in each woodland. Even if the forest is only 1 km2 that could be a pretty large task. So we sample. We sample a number of areas in each forest, count the number and frequency of species, extrapolate to the whole area being considered and calculate the species diversity. Simple. But the sample must not be biased and must be representative of the whole population.

Things to consider

• Larger samples are likely to be more representative of the whole population. However too large and there is no longer an advantage to sampling. There needs to be a balance between a sample that is large enough to statistically valid data but not so large that it is time consuming and expensive.
• The number of samples to be taken depends on what you are sampling (see below).
• Avoid bias – this is done through sampling strategies.

Theory of Knowledge

Sampling is an essential part of many investigations. Sampling is more accurate in the natural sciences than the human sciences - discuss.

There are three main sampling techniques used in ESS, random, systematic and stratified. The samples may be points, line or areas depending on what data is being collected.

How many sample points? What is 'enough'?

This is always an important issue. The greater the number of sample points the more reliable the study but that has to be balanced against available time and money.

In some studies it is easy to calculate the number of sample points needed. In ecological surveys that are assessing the number of species in a given area, sample size is ascertained by plotting the cumulative number of species recorded against the number of samples taken.

Figure 1. How to determine sample size in a selected area.

In Figure 1 the number of species recorded in the first sample was 7. Five new species were found in the second sample giving 12 in total. Then the species total peaked at 21 in sample 6 and did not increase any further. That means for any further surveys in that area 6 sample points is enough.

This is only one example of a way to establish how many samples to take at a particular site and only works if you are studying the same site over a period of time. In other cases there are different “rules” which will be explained in other sections.

When and what?

Sampling establishes when and where to measure the biotic and abiotic factors and/or how they change. Spatially such factors may change along an environmental gradient like up a mountain or away from a river. Temporal changes may be measured through succession (though that is over a very long period time) or biotic and abiotic factors can be measured as part of an EIA. The method used to measure these factors is covered in the following sections.

International-mindedness

Is sampling the same in all countries?

Sampling strategies

Random sampling

This technique does not involve any subjectivity and is thus the least biased method. Every item has the same chance of being selected through the use of random numbers. The numbers can be generated using a graphic display calculator, excel or a random numbers table.

Methodology

For random sampling of an area in an ecosystem you will need a map with a numbered grid over it. This can then be used as a base to identify sampling locations. This explanation is based on Figure 1.

Figure 1. Random sampling.

Random points, lines and areas

Using one of the methods generate pairs of random numbers.

• A - 1,1
• B - 2,0 – there is no point B in Figure 1 because there is no 0 on that axis of the map. If that happens ignore that number and move on.
• C - 3,3

It does not matter how you use the pair of numbers to identify the points so long as you are consistent. So in this example the first number is for the numbers along the bottom and the second number is for the numbers up the side. The numbers identify the bottom left hand corner. These can then be used to identify points, areas and lines.

• Random points are identified by the pair of numbers, point A and C on Figure 1.
• Random areas are identified by using the pair of numbers to give the bottom left corner of the square. So if the random number was 5,6 square D would be sampled.
• Random lines are achieved by generating two pairs of numbers and then joining them. So a pair of points 2,2 and 3,7 would mean you sample along line E.

Systematic sampling

This is where samples are chosen in a regular way. This technique is often referred to at the nth method, using this method you may select:

• Every 5th person that passes you by. Standing in a busy shopping area you would count four people then stop the 5th person and ask them to complete a questionnaire.
• Every 7th house in the street. Starting at the beginning of a street you may decide to study the plants in the garden of every 7th house.
• Every meter along a transect line. Lay down a transect line and note down the type of plant that touches the line at each meter mark.
• Samples every 30 minutes through the day. If you are studying the change in temperature of an area you could take the temperature every 30 minutes.

Figure 2. Systematic sampling lines.

Stratified sampling

This technique is used when the population is known to contain subsets. It is important to know the size of the subsets in the whole population so that your sample reflects the same proportions. For example the human population being studied has:

• 30% under 21 years old.
• 50% between 22 and 70 years old.
• 20% above 70 years old.

The stratified sample should have the same proportions in each age group.

Stratified sampling does not stand-alone but is combined with random or systematic sampling. Once the sub sets and their size are identified an appropriate sampling method can be used to select sample points, lines of areas.

Stratified systematic sampling

In this example the environmental values systems of different year groups in a school is studied.

1. Design the questionnaire to establish the EVS of students.
2. Find out how many students in each year group so you know how many you have to sample.
3. Select every 5th student to complete the questionnaire until you get a minimum of 30 responses in each year group.

Stratified random sampling

In Figure 3 the percentage of land in each area is given. You could use random line, point or area sampling to decide where to sample. Whichever method used the number of sample point should be proportionally the same as that of the whole area. If random points are selected there should be 32 in the meadow, 28 in the woodland, 21 in the grass and 19 in the hyacinth field. You could also use the other random sampling techniques.

Figure 3. Stratified random sampling.

Theory of Knowledge

How can we know what sampling strategy is going to be most effective?

Quadrats and transects

Quadrats and transects are basic measuring instruments and techniques in ecological studies used in conjunction with sampling.

Quadrat

A quadrat is an appropriately shaped plot used to identify the area you wish to study. They are usually square or rectangular but, they can be any shape you want so long as it is the same throughout the study. Remember you can't use a quadrat to directly sample things that fly or walk!!

Quadrat size

The size of the quadrat will be dependent on the organisms being studied. Small organisms = smaller quadrats and larger organisms = larger quadrats.

The smaller quadrats are usually an actual physical structure made of metal, wood or plastic. They range in size from 10 × 10 cm square for the study of small plants such as lichens to 1 × 1 meter for larger plants. These smaller quadrats may be sub-divided using string to make the assessment of percentage cover easier. If you can divide your quadrat into a grid with 100 smaller squares then estimating percentages becomes easier.

Figure 1. 1 × 1 meter quadrat subdivided into 1% squares.

A quadrat bigger than 1 meter square is too hard to carry so for larger study areas the quadrats are areas staked out using pegs and string. They may be 10 × 10 meters or larger and are used for investigations on larger vegetation such as bushes and trees. The same principles that apply to the smaller quadrats apply to the bigger ones.

What are quadrats used for?

Quadrats can be used to study plants and non-motile animals or ones that do not move very much such as limpets on the seashore. The quadrat is placed at whatever point is decided and the following may be assessed.

The number of individuals of a particular species that are seen in the quadrat. This sounds easy enough and with certain organisms, it is. Individuals in some species are easy to identify - flowers, trees and slow moving animals like limpets and barnacles are identifiable. What happens with grass, do you count every blade of grass? A single individual grass may stretch over a large area as it is inter-connected by roots that pass under ground and send up new shoots. It is nearly impossible to establish where one individual ends and the next starts. In this case choose a very small quadrat, count the individual blades as accurately as possible then multiply up for the entire area.

Percentage frequency is how often a particular species appears in an area. This is best done with a gridded quadrat, as it is easy to count how many squares the species appears in. This technique has the same problems as counting individuals.

Figure 3 shows the organisms on a seashore - barnacles and mussels. In this example assume we are studying mussels. Once an appropriate sampling strategy is established a number of 1 × 1 meter quadrats can be placed and the number of mussels in each one can be counted. That gives the number of mussels per meter squared. Once the data from a minimum of five quadrats has been recorded the mean can be calculated per square meter and then multiplied by the study area to achieve an estimate of the approximate number of mussels on the seashore.

Figure 2. Barnacles and mussels on the seashore.

This basic method can be used with quadrats in many different situations.

1. Take a minimum number of quadrat samples, usually at least five.
2. Calculate the mean from those samples.
3. Extrapolate for the whole study area.

Population density – once you know the number of individuals in an area it is a simple calculation to establish the population density of that species. If you are using a quadrat that is 1 × 1 meter and there are 30 daisies in the quadrat then the population density is 30 daisies m-2. If the quadrat is not 1 × 1 meter do the maths to work out how many individuals in a meter squared. But be careful when linear dimensions double, area is quadrupled. In Figure 3 the blue quadrat that is 0.5 × 0.5 meter fits in to the larger blue-green quadrat four times, so if you have 10 daisies in the 0.5 meter square quadrat you have 40 daisies m-2.

Figure 3. Quadrats and population density.

Percentage cover is easily assessed if the quadrat is subdivided into 100 smaller squares – each square represents 1% coverage. It is possible to give the actual percentage coverage by each species by counting the number of squares covered. If half a square is covered then it can be estimated. Alternatively you can use the ACFOR score shown in Table 2.

Theory of Knowledge

Most of the techniques for using quadrats are subject to margins of error. To what extent does this compromise the data we gain?

Transects

The video gives a very simple explanation of how to place a transect line.

Types of transect

There are a number of different transects.

Line transects

A line is placed according to a sampling strategy and then the vegetation that touches the line can be recorded at intervals, usually every 1 meter.

Random sampling - If the area being studied is uniform with no discernable patterns (Figure 4a) then the lines can be randomly placed. There are many way of doing this, one way would be to generate a random number and find that point on the map. Generate a second random number. Then draw a line through the two points.

Figure 4a. No discernable pattern in the vegetation.

Stratified sampling – in areas where there are known subsets then the number of lines placed in each area must reflect the proportions seen in the whole area.

Systematic sampling – if the study area is an environmental gradient then transect line must be placed along that gradient (Figure 4b).

• Transect line A goes from the peak (dark brown) down the slope to the bottom of the valley.
• Transect line B goes from one peak down the slope to the bottom of the valley and back up the other side.

Such changes in elevation are likely to cause changes in vegetation. At set intervals transect lines can be laid out. The intervals will depend on the size of the study area – maybe three transects at 10-meter intervals across the gradient.

Figure 4b. Obvious environmental gradient.

Belt transects

These use a quadrat to create a belt of sampling. The placement of the belt can be achieved just the same as for a line transect. Once the line of the transect is determined a quadrat is used to create a belt of sampling (Figure 5). Recordings may be continuous or interrupted.

Figure 5. Belt transect.

International-mindedness

Quadrats and transects are used globally but are they used in the same way and for the same thing?

Abiotic factors

There are many abiotic factors that can be investigated in an ecosystem depending on the type of ecosystem. It is possible to investigate spatial and/or temporal changes shown in Table 1.

Examiner Tip

You must be able to evaluate the methods to measure at least three abiotic factors. Very often the method is similar it is just the instruments that change. So make sure you check what the question is asking – is it an evaluation of the instrument or the actual method.

Theory of Knowledge

There are hundreds of different abiotic factors that could be measured and many different ways to measure them. How can we know which ones we should be measuring?

Probes

With current levels of technology measuring the abiotic factors of an ecosystem can be relatively straightforward and many of the smartphones now have apps that allow you to collect a lot of data – though their reliability may be questionable. There are however very reliable data loggers and digital probes that allow you to quick accurate readings. Many of these devices have interchangeable probes that allow you to take measurements of several different abiotic factors. Salinity, pH, temperature, dissolved oxygen, light intensity and soil moisture and mineral content all vary over time and space and can all be measured using digital probes and/or data loggers.

In each case the site for the measurement should be determined and as many factors as possible should be controlled or kept constant. Things to consider:

• If you are investigating changes through the day make sure the probe is held at the same spot each time you take the measurement.
• If you are investigating changes through the week/month/year then take the measurement at the same time of the day every time.
• If you are investigating changes over space then always take the measurements at the same time.
  • Changes over horizontal areas mean that the probe must be at the same height (or depth) each time.
  • With changes in altitude try and keep the surroundings similar – do not take one reading under a tree and another in the open.
• Always repeat the measurement five times and take the mean of the five readings.

Probes are obviously a recent addition to the scientists’ catalog of instruments – see if you can find an alternative, non-digital method to measure three of the abiotic factors given in Table 1.

Some abiotic factors require more conventional fieldwork techniques to assess for instance turbidity, low velocity, wind speed, slope angle and soil texture/particle size.

Turbidity

Figure 1. Secchi disk ready for use.

"Floating Secchi Disk" by usacehq is licensed under CC BY 2.0

Turbidity is the cloudiness of a water body. It is measured using a Secchi disk - created by Angelo Secchi in 1865 to measure the transparency of water bodies. It is a black and white disk 20, or 30 cm in diameter (Figure 1) mounted on a line or a pole. The clearer the water the lower the turbidity and the higher the Secchi depth will be.

Method:

1. Stand or sit on the shaded side of the boat or dock.
2. Slowly lower the Secchi disk into the water until it is no longer visible.
3. Record the depth at which it disappears – this is called the Secchi depth.
4. Repeat at least 5 times for accuracy and take the mean of the 5 readings.
5. The same person must take all the readings and they must be in the same position every time.

Flow velocity

The speed at which a river flows can be measured with a flow meter or a simple float. There are a number of different types of flow meter and the majority of them work on the basis that you put an impellor in the water and the speed at which it rotates tells you the speed at which the river is flowing in m/sec. Figure 2 shows the impeller of a flow meter, the impeller is placed in the water and then a meter is used to give a reading of flow velocity. This should be repeated five times and the mean calculated.

Figure 2. Flow meter.

Flow velocity can also be measured using a float (pooh stick). This method involves timing how long it takes a float to cover a set distance.

Method:

1. Select a straight section of the river and measure a distance of 10 meters. Place a marker on the bank at the start and finish of the section. If there is no straight section that is 10 meters long then less is fine.
2. Person A stands at the start point and places the float in the water just above the marker.
3. As the float passes the start line person A starts the stop watch.
4. Person B tells person A when the float passes the finish line and the stop watch is stopped.
5. The float should then be caught and sent back to the start.
6. This is repeated 5 times to give a mean value.
7. Divide by 10 (or however many meters the float traveled) to work out how long it takes the float to travel 1 meter. This is the multiplied by 0.85 to adjust for the fact that the velocity is taken at the surface.
8. This gives seconds/meter NOT meters/second, so the higher the value the SLOWER the river velocity.

The best float is an orange as it floats just below the surface and gives a more accurate indication of the speed of the river. Alternatively aluminum foil can be scrunched up in to a ball that floats just below the surface of the water, berries also work well.

Figure 3. Pooh sticks.

Wind speed

Wind speed is measured using an anemometer, there are many different types and Figure 4 shows a small hand held variety with a digital reading. These are very easy to use - simply hold them in the path of the wind and let the wind blow through the fan at the top. The reading will then give wind speed in meters/second. Repeat five times and calculate the mean. Ensure that you are away from obstacles and that the anemometer is held at the same height each time.

Figure 4. Anemometer.

Slope angle

Slope angle is measured using a clinometer - these can be bought or made using a protractor, a string and a weight (Figure 5).

Figure 5. Homemade clinometer.

Method:

1. Take two 1 meter poles and place them at least 5 meters apart on the slope.
2. One person stands at the top pole and two people at the bottom one.
3. Place the clinometer close to the top of the pole and look up at the top of the other pole. The weighted string will drop straight down and the third person can read the number of degrees.
4. With a home made clinometer the slope angle is the number of degrees away from 90° line.
5. Repeat 5 times and calculate the mean.

Soil

This video explains how you can assess soil texture by getting your hands dirty and the soil wet and then running a series of tests on the soil.

The size of the particles in a soil determines its texture which is a very important aspect of soil. Soil texture can be determined in the field using the "Hand identification chart for soil texture analysis" If you want to give it a go, follow the video or this link.

Theory of Knowledge

The methods to assess soil texture are very subjective. Do subjective methods fit in the scientific model?

Method:

An alternative way to study soil texture in the lab.

1. Take a sample of soil and place it in a bottle.
2. Add water and shake vigorously until all the soil is broken down.
3. Place the jar on a shelf and leave it to settle for a couple of days.
4. Measure the depth of the layers that appear. The coarser heaviest sediments will settle first (sand and gravel) and the finer lightest elements will settle last (clay).
5. Calculate the percentage of each particle size.

Figure 6. Soil layers.

International-mindedness

These instruments were developed in different countries - look into the history of a couple of them.

Biotic factors

There are a number of biotic factors that can be investigated in an ecosystem.

• The organisms can be identified and counted.
• Biomass can be estimated for different trophic levels.
• Diversity can be assessed and changes in space and time investigated.

Identifying organisms

Organisms can be identified using keys, by comparing them to a know specimens or using scientific or local expertise. The easiest keys to use and design are dichotomous keys – which are a series of paired questions based on the physical characteristics of an organism. There are a number of basic rules that must be followed when designing these keys:

1. Use only observable characteristics, things that you can see.
2. Give specific measurements if you are talking about size or weight. Is the insect longer than 5 cm? Is the leaf longer than it is wide?
3. Use very specific language, no vague statements like is it long? Long to one person is not the same as long to another person.
4. Beware of using colour as some organisms change colour during the year. The Arctic fox is white in winter but brown in summer.
5. You can use paired statements (as in the video) or yes/no questions as in Figure 1a.

Figure 1a. A variety of organisms.

The organisms in Figure 1a above can be identified using the dichotomous key in Figure 1b below.

Figure 1b. Dichotomous key for Figure 1a.

Theory of Knowledge

In view of the disadvantages associated with dichotomous keys consider their value in scientific studies.

Measuring biomass and energy

Trophic levels are the feeding levels in a food chain and it is possible to investigate the amount of biomass and energy in each level. The major problem is that biomass is measured as dry weight and the measurements can be very destructive. For instance if you want to know the biomass of a tree you would have to chop it down, remove the water content and then weigh what is left. Dry weight is necessary because the water content of different organisms can vary enormously.

Figure 1. Trees are chopped down and dried to measure biomass.

Theory of Knowledge

Measuring biomass requires a great deal of destruction - can this be justified in the name of scientific investigation?

Measuring biomass in the trophic levels

It is really only possible to measure the biomass of vegetation as you cannot take the dry weight biomass of animals without killing them – and that is not ethical. It is possible to capture the animals and weigh them but that may cause stress and is inaccurate due to the variability of water content. Capturing the animals is dealt with later in this section.

The method to measure biomass of vegetation will vary slightly depending on the size of the plants but the overall method is very similar.

Method for small vegetation:

1. Decide on an appropriate sampling strategy for the area of study.
2. Identify five quadrats (size will depend on the vegetation but 1 × 1 meter is ideal).
3. Harvest all the vegetation in one quadrat.
4. Remove soil, insects and other non-plant material.
5. Wash the vegetation.
6. Place the sample in an oven to dry over night.
7. Weigh the sample then return it to the oven.
8. Repeat steps 6 and 7 until the weight of the sample remains constant.
9. Repeat steps 3 to 8 for all five quadrats and calculate the mean dry weight biomass m-2.
10. Multiply by the study area to estimate the biomass for the whole area.

The same method can be applied to trees but instead of selecting quadrats select five typical branches, estimate how many branches are on the tress and extrapolate for the whole tree.

Figure 2. Measure the biomass of branches and extrapolate.

Measuring energy in trophic levels

The energy in a trophic level is taken as the productivity. Once again it is easier and more ethical to take the productivity of plants than it is animals due to the dry weight problem. Net primary productivity (NPP) is calculated using the following formula. Where GPP is gross primary productivity and R is respiration.

NPP = GPP – R

The method used to measure these components is partially direct and partially indirect. GPP is all the biomass that is produced before respiration and it is not possible to measure that. What we actually see in the plant is NPP – what is left after repair and respiration.

Method:

In Figure 3 there are three identical quadrats.

• All the same vegetation.
• All the same size.
• Quadrat B is covered in black plastic sheeting – that means that plants will not be able to photosynthesize, only respire.

Figure 3. Three identical quadrats to measure productivity.

1. Harvest all the vegetation in quadrat A.
2. Remove soil, insects and other non-plant material.
3. Wash the vegetation.
4. Place the sample in an oven to dry over night.
5. Weigh the sample then return it to the oven.
6. Repeat steps 4 and 5 until the weight of the sample remains constant.
7. Leave quadrat B and C for a month (or a week depending on how fast the vegetation grows).
8. After a month repeat steps 1 to 7 for quadrats B and C.

Assuming that quadrat A and C are identical, the increase in biomass over the month would represent the NPP of that vegetation. So quadrat C biomass minus quadrat A biomass gives the NPP.

In this example:

NPP = quadrat C – quadrat A

= 200 – 100

= 100

The vegetation in quadrat B has not been able to photosynthesize so has lost biomass through respiration. So assuming quadrat B was the same as quadrat A at the beginning it has lost 50 g m-2 of biomass through respiration. So simple maths gives us the following:

NPP = GPP – R

100 = GPP – 50

150 = GPP

It is therefore possible to estimate the NPP, GPP and R for a given type of vegetation.

Evaluation of measuring productivity

The advantages and disadvantages that apply to measuring biomass are the same for productivity but with a few extra problems:

• It is highly unlikely that all three quadrats are identical as regards the vegetation.
• This can really only be done once as three quadrats are needed.

Measuring secondary productivity

Secondary productivity is that of the animals in an ecosystem. Given that it is unethical to kill animals, any measurements for secondary productivity will be inaccurate due to the variations in water content of different specimens.

The various elements of secondary productivity that need to me measured are gross secondary productivity (GSP) which is the food eaten – fecal loss. Net secondary productivity is GSP – R (respiration).

Figure 4. Animal biomass.

Method:

It is possible to estimate GSP by knowing the weight of the food eaten and the weight of fecal losses, NSP by knowing the weight of the organism at the start and the end of the investigation and respiration can be extrapolated.

1. Keep the organism under study in a cage.
2. Weigh it at the beginning and end of the study (that gives NSP).
3. Weigh all the food it is given and all the feces is produces (that gives GSP).

• Weight at start: 3.0 kg
• Food eaten: 5.0 kg
• Fecal losses: 4.0 kg
• Weight at end: 3.5 kg

GSP = food eaten - fecal loss

GSP = 5 – 4

GSP = 1

NSP is the weight at the end minus the weight at the start.

3.5 – 3 = 0.5

NSP= GSP – R

0.5 = 1 – R

R = 0.5

International-mindedness

Are the same methods used everywhere in the world? Do different EVS's impact the data collection methods use din different places?

Species diversity

Species diversity is a function of the number of different species and their relative abundance and it is calculated using the Simpsons diversity index.

There are a number ways to show species diversity data.

Kite diagrams show the spatial changes in species along a transect. Figure 1 is a very simple kite diagram with only three species shown but they can show many more. They are a very effective way to show spatial changes in species diversity.

• The width of the horizontal bars shows how many of each of the species were found at that location. E.g. at the foot path there was a lot of bare ground, some of species A, very few of species B and none of species C.
• The bars will disappear if a species is absent e.g. species B disappeared at the location 2 meters from the footpath.

Figure 1. Kite diagram to show species diversity changes away from a footpath.

It is also possible use a bar graph to compare changes in species diversity over time or space as in Figure 2. Again the graph can be used to show several different areas/times.

Figure 2. Bar graph to show differences in diversity in two ecosystems.

Motile organisms

Motile animals are ones that are mobile. There is a wide range of ways to estimate the abundance of motile animals. Methods may involve direct counting and sampling or indirect techniques such as the Lincoln index covered in the next section. Either way there may have to be some method to capture the animals, at least temporarily for the count.

Capturing animals

This section starts with a general evaluation of capturing animals - this is to get you thinking as you read through the methods. Is it necessary to do this? How else can we count animals? What other advantages and disadvantages are there? It must be remembered that any method used to capture the animal must be as harmless as possible. Completely harmless capture is unlikely but there are some techniques that are less harmful. There are numerous humane techniques to catch animals for study then release them.

Traps

The trap shown in Figure 1 can come in a variety of sizes to catch anything from a mouse to a bear. Though capturing a bear does come with a few problems and is probably not that desirable at this stage. These traps are usually baited with the animals favorite food and left overnight or for up to 12 hours. They must be checked regularly so that the animal is not stressed and does not die of thirst or hunger. A problem with this type of trap is that animals in the local area can become "trap happy" they return to the trap regularly for food and a secure bed, this can make them habituated to humans which can cause problems.

Figure 1. Humane animal trap.

Nets

Nets are often used to catch birds, bats and fish. Whereas the animal trap in Figure 1 can be baited and left for a short time, nets must be cleared immediately as the animals may get stressed and die. This type of capture involves setting the net, staying at the catch site and doing the count immediately. This type of netting is very stressful for birds and bats and can result in injury.

Figure 2. Humane bird nets must be cleared immediately.

Both of these methods of capture may involve marking the animal in some harmless way, this is to avoid double counting.

• Birds and bats may have an identification ring placed on their leg.
• Small mammals such as mice and voles can have a small patch of fur clipped.
• Fish may have a fin clipped.

Sweep nets may be used to capture flying insects and stream invertebrates. In the case of flying insects the net is swept through the vegetation for a set period of time and then the insects caught in the net are identified and counted. This is a simple technique but it is easy to miss a lot of insects in dense vegetation and thus get inaccurate counts. It can also be dangerous to antagonize insects as they may bite or sting.

Figure 3. Sweep net used to capture flying insects.

Be Aware

It can be dangerous to touch insects (they may bite, sting or be venomous) so you should use a pooter to collect/sort them. If the insects are larger you can use tweezers. The insects do not need to be retained so once they are identified, counted and recorded you can let them go.

Figure 4. Pooter for collecting small insects.

Theory of Knowledge

Capturing wild animals can be very stressful and even lethal for them. Is it ethical to stress animals just to find out how many there maybe?

Nets are also used in the study of stream invertebrates through a method called kick sampling.

Method:

Kick sampling is best done with two people but can be done with only one person if necessary. With two people:

1. Two people stand in the stream approximately one meter apart.
2. The person with the net stands downstream making sure the net is touching the bottom of the stream.
3. The person without the net kicks the sediments in the bottom of the river and moves slowly towards the net. The kicking will disturb any stream invertebrates and maybe a few small fish and they will be caught in the net.
4. Empty the contents of the net into a large white collection tray with stream water.
5. Sort the organisms in to different cups containing stream water (small paint pallets work well too). You can move the organisms with a pooter or a paintbrush.
6. The number of each type of organism can be counted and recorded.
   1. All the organisms scan then be release back into the stream close to where they were caught.

Figure 5. Kick sampling.

Problems can arise with this method if you are comparing sites close by and the organisms from one site drift in to another study area. The kick sampling is also prone to damage the invertebrates and stir up sediment that reduces clarity of the water. Hence abiotic factors must be measured first e.g. water clarity/turbidity.

Pitfall traps

Pitfall traps are another method for catching animals for investigation. The basic principle is that it is a container sunk into the ground into which an organism can fall. Figure 5 shows a small pitfall trap designed to capture ground dwelling insects. However a pitfall trap could just as easily be a very large bucket that could catch small mammals.

Figure 6. Pitfall trap.

Things to remember with pitfall traps:

• NEVER put liquid in the bottom as that may drown the organism. The aim is not to kill them, just observe them.
• Punch a few small holes in the bottom to allow water to drain out. Not too large so the organisms can’t escape.
• Make sure there is food and bedding in it.
• Make sure there is a cover of some description to keep sun and rain out.
• Set them out in an area where you think the organisms are active.
• You can place a barrier that pushes the organisms towards the pitfall trap and that may increase the catch. The barrier may be a line of sticks leading towards the pitfall trap.

Pitfall traps can capture venomous organisms such as scorpions so care must be taken when investigating the contents of the traps.

Aerial photography

Aerial photography can be used to investigate larger animals that live in open grassland environments. It is useful to estimate the number of large herbivores such as horses, buffalo, elephants or kangaroos and carnivores such as lions and cheetahs. It is of no use for animals that live in dense forest.

Figure 7. Aerial shot of grazing animals in a grassland area.

Figure 7 shows a herd of cows in a field - this is a small area but the technique can be used over very large areas. Once the study area has been identified aerial photographs can be taken. A grid can then be drawn over the photographs and a sample of squares identified using an appropriate sampling strategy - in this case random sampling would be best. The animals are then counted in at least five squares, the mean calculated and the number of animals in the whole study area extrapolated.

International-mindedness

Can similar ecosystems from different countries be compared?

Lincoln index

The Lincoln Index is an indirect method by which the size of an animal population can be estimated. It is also called the capture/mark/release/recapture method – which gives you some hint as to how it works. It can be used on just about any organism that can be caught and marked though due to ethical issues this is not always advisable eg. for large mammals as catching and marking can cause injury and distress. Use is becoming more restricted to invertebrates and small mammals.

Method:

1. In your area of study capture as many of the study animals as possible. Methods for capture have been discussed earlier in this section.
2. Mark the organisms in some way that does not harm them or make them more or less prone to predation.
   • Insects can be marked with a non-toxic spot of paint/dye.
   • Mammals can have their fur clipped.
   • Fish can have a fin clipped.
   • Birds and bats may have a ring attached to their leg.
3. Record the number of animals that were caught and marked.
4. Release the animals back into their environment and give them sufficient time to reintegrate into the population (one week to a month). Fast moving animals like mice will reintegrate quicker than slow moving ones such as snails.
5. Resample the population and record the number of animals that are marked and unmarked.
6. Use the following formula to calculate the total population:

N = n1 × n2 / m2

Where:

• N = total population.
• n1 = number of animals marked in the first capture and released.
• n2 = number of animals recaptured (second sample).
• m2 = number of animals marked in the recapture (second sample).

If the number of animals caught in the second sample is less than eight then the estimate is not likely to be accurate.

Try for yourself!

A group of students are trying to estimate the number of mice in a meadow. They conducted a capture/mark/release/recapture method and recorded the following numbers.

• n1 = 38
• n2 = 15
• m2 = 9

Using the Lincoln index to estimate the number of mice in the meadow.

» Click to view answer

Evaluation of Lincoln index

There are a number of assumptions linked to this method and they are that:

• The proportion of marked animals in the second sample is the same as the proportion of marked animals to unmarked animals in the whole population.
• Enough time has elapsed to allow full mixing of marked and unmarked animals.
• All animals are just as easily caught – that is unlikely as some animals may be more easily caught in both samples giving a biased sample.
• The population is closed and that there is no immigration or emigration.

There are also a few problems associated with the Lincoln index:

• Capturing the animas may injure them or alter their behaviour.
• The mark may be toxic to some animals but not others – you may not know until it is tested on the organism under study.
• Marks may rub off between release and recapture.
• Marks may make the animal more or less attractive to predators.
• Some animals become trap happy (causing an overestimation of numbers) whilst others become trap shy (causing an under-estimation).

Theory of Knowledge

To what extent does the act of observing the animals (capturing and marking them) change the results?

Applications and investigations

The techniques outlined in this subtopic all come together to allow the investigation of ecosystems, parts of ecosystems, changes along an environmental gradient or changes in an ecosystem caused by human activity.

In this section, using a specific example, we will look at how to conduct a study using some of the techniques you have learnt about. This study investigates how to conduct a study into changes in an ecosystem as you move away from a river (environmental gradient).

The next section will outline how to conduct a mini EIA, which will look at how human activity impacts an ecosystem.

This is a very small snapshot of the myriad of possible investigations that you can do. What you are able to study will be controlled by where you live, the time of year, available equipment and many other factors. You can never conduct all the possible studies but you can learn about how to conduct them. The techniques you have learnt about in this subtopic can be applied to many different investigations and you can use them when you plan and conduct your investigation for your internal assessment.

Examiner Tip

Remember - ESS is about environmental systems and societies and to score well in your internal assessment you must combine both of those elements and look at an issue to which you can suggest a possible solution.

Changes along an environmental gradient

An environmental gradient is the gradual change in the biotic factors through space. An environmental gradient is present as you move up a mountain, away from a stream or a road. These changes in the abiotic factors will cause changes in the biotic factors and these can all be measured.

Figure 1 will be used as the example of an environmental gradient throughout this explanation. Due to the fact that we are expecting a set of changes along an environmental gradient, the best way to investigate the changes is through the use of transects and systematic sampling.

There is a wide range of biotic and abiotic factors that could be studied including:

1. Abiotic factors:
   • Temperature – air and soil
   • Humidity
   • Light intensity
   • Wind speed
   • Soil – pH, texture, moisture content, organic content
2. Biotic factors:
   • Species diversity
   • Percentage cover of species
   • Percentage frequency of species

Theory of Knowledge

How is it possible to know which abiotic and biotic factors need to be assessed?

Figure 1. Transect lines for environmental gradient near a river.

Figure 1 shows two possible sets of transect lines. There is no scale given but let us assume that the three shorter transect lines on the right are 20 meters long and two longer ones on the left are 50 meters in length. Ideally three is the minimum number of transect line but two longer ones may be needed to show patterns more clearly. The spacing may be systematic or it may be selected to make sure all vegetation types are in the study area. The latter is acceptable with environmental gradients as you are studying the changes.

​Once the transect lines are established a decision must be made as to the frequency and type of sampling. In this case a sampling interval of 5 to 10 meter interval is acceptable and quadrats will be the most efficient. The 5 meter interval will give more reliable data but the 10 meter interval can be used if time constraints are an issue. The method to use transect and quadrats is covered in section 2.5.3.

When large amounts of data are being collected it is often done as a group effort so it is important to set up good data collection tables (Table 1). Make sure there is somewhere to record the transect number and the quadrat number – you will not remember these details at a later stage. It is also important to make qualitative observations as you do your raw data collect – these are notes about the environment, changes in weather, problems encountered.

Measuring the abiotic factors

Method for measuring air temperature, humidity, light intensity and wind speed

Air temperature, light intensity and humidity are all measured using a probe or data logger and they will be very similar for a whole quadrat so measurements can be taken at the center – where the red spot is on Figure 2. At a fixed height (1 meter above the ground) take five readings for each factor and record the results on your raw data table.

Figure 2. Possible sample points for abiotic factors.

Theory of Knowledge

Consider the problems caused by the changes in factors that can not be controlled during fieldwork research. What impact will they have on the results of investigations?

Method for soil samples

Soil may show some variation over the quadrat hence soil samples to measure pH, texture, and temperature should be taken at different points in the quadrat. The sampling strategy could be random or systematic. The possible points for systematic sampling are shown as 1 – 5 on Figure 2.

Soil temperature can be measured using a probe or a soil thermometer (analogue one). The instrument is inserted into the soil at the sample point to the same depth each time and the temperature recorded.

To investigate soil pH and texture you need a soil sample. When dealing with quadrats the simplest way to take a soil sample is using a soil auger. These are like a giant corkscrew – they are screwed into the soil and then drawn straight out with a core of soil – as shown in Figure 3. There are smaller hand held versions but Figure 3 is a good illustration of a soil core.

Figure 3. Large mechanical soil auger.

To measure soil pH the soil needs to be mixed with distilled water then a probe can be used to determine pH. Assessing soil texture was covered in section 2.5.4. It is possible that a soil sample needs to be taken back to the laboratory for these measurements. If this is the case:

1. Use the auger to take a soil sample.
2. Place a portion of the sample in to a Ziploc bag and seal immediately.
3. Label the Ziploc bag immediately with the transect number, quadrat number and sample number – e.g. T1, Q3, S5 would mean transect 1, 3rd quadrat and 5th sample. It may be a good idea to note the date too.

Other soil investigations

It is also possible to investigate moisture content and organic content of the soil once back in the lab.

Method:

1. Place a sample of soil in a small crucible.
2. Weigh the soil plus the crucible and record the weight.
3. Place in an oven at 90°C for 24 hours.
4. Repeat steps 2 and 3 until the weight of the sample is constant – this is the dry weight.
   • The difference between the starting weight and the final weight is the moisture content.
5. Once the soil has lost all of its moisture place the crucible in the flame of a Bunsen burner to burn off the organic matter in the soil.
6. Repeat steps 2 and 3 until the weight of the sample is constant.
   • The difference between the dry weight and the final weight is the organic content of the soil.
7. As usual both measurements should be repeated at least five times and the mean calculated.

Figure 4. Soil samples drying.

Example

• Original weight of the sample: 35 g
• Dry weight: 20 g
• Weight after organics are burnt off 15 g

Moisture content:

• 35 – 20 = 15
• Of the original weight of soil 15 g is water. Moisture content is expressed as a percentage so 15/35 × 100 = 43%.

Organic content:

• Dry weight – final weight.
• 20 – 15 = 5
• 5/20 × 100 = 25%

Measuring the biotic factors

Realistically, the only biotic factors that can be easily measured along an environmental gradient are those to do with plants. The techniques for investigating animals are not in small quadrats such as those used in this investigation.

Figure 5. Plants species diversity.

Species diversity is measured using Simpsons Diversity index.

D=N(N−1)/∑n(n−1)D=N(N−1)/∑n(n−1)

Where - N is the total number of individuals and n is the number of individuals in each species.

So if you are investigating an environmental gradient you could measure the change in species diversity as you move away form the river. To calculate the Simpsons diversity index you would need to record the number of individuals of each species in every sample quadrat.

Alternatively the percentage cover and percentage frequency of the various species of plant can be recorded in each quadrat.

International-mindedness

Can the results of investigations along an environmental gradient be compared between different groups of students in different areas of the world?

Mini environmental impact assessment

As the human population expands so does the built environment and new schools, roads, houses are needed. Many developed countries insist on an EIA. An investigation of the proposed development site prior to any work being done. The EIA starts with a baseline study to establish what is present in the area and what impact the development will have on the natural and human environment.

Developments can take place on Greenfield sites, one that have never been built on, or Brownfield sites – ones that are already developed. This study will consider how to conduct an EIA in an area like Figure 1 - a Greenfield site.

What data do you need?

All the factors that were measured in the environmental gradient must be measured in an EIA but the sampling techniques will be different and there will need to be an assessment of what animals are present. An appropriate sampling technique would be random sampling or stratified random sampling. To establish the number of sample points needed use the technique described in section 2.5.1 – keep sampling until no new plant species appear.

Figure 1. Wooded area ready for development.

At each sample point collect all the abiotic and biotic data and make sure you have a very clear detailed raw data collection table.

Theory of Knowledge

To what extent does qualitative data add value to scientific investigations?

Investigating animals

The methods to investigate animal populations were discussed in section 2.5.8 and the choice of technique will depend on what animals are likely to be in the area:

• Traps can be set for small mammals.
• Sweep nets would be used for flying insects.
• Nets for bats and birds.
• Pitfall traps for crawling insects.

The animal capture techniques should be set of for approximately a week to ensure all organisms are included in the study.

With an investigation like this it is possible to survey the public about how they feel about the area, but you must never suggest that a development is going to take place. You can conduct what is called a bipolar analysis - a common tool to survey opinions. A list of questions can be graded from positive to negative to give a landscape/area score.

A word of warning, these are difficult to design as different people have different opinions as to whether something is good or bad. To make sure it is going to work conduct a trial run first. It is advisable to miss out the 0 as this gives people middle ground to avoid giving a actual opinion. Once you have asked at least 30 people to complete this survey you can calculate a mean value for a particular area. If the area score well then developing it may have a negative impact on the local human population.

International-mindedness

Attitudes about the perceived positives and negatives may vary between countries, cultures and age groups - how will this impact the results of an investigation.