2.5 - Practicle Work

Question 1

how can organism in an ecosystem be identified

Answer 1

Organisms in an ecosystem can be identified using a variety of tools including keys, comparison to herbarium / specimen collections, technologies and scientific expertise.

Question 2

Define sampling strategies

Answer 2

Sampling strategies may be used to measure biotic and abiotic factors and their change in space, along an environmental gradient, over time, through succession or before and after a human impact, for example as part of an EIA.s

Question 3

Why should measurements be repeated

Answer 3

Measurements should be repeated to increase reliability of data. The number of repetitions required depends on the factor being measured.

Question 4

What are methods for estimating the biomas and energy trophies levels in a community

Answer 4

Methods for estimating the biomass and energy of trophic levels in a community include measurement of dry mass, controlled combustion and extrapolation from samples. Data from these methods can be used to construct ecological pyramids.

Question 5

What are some methods for estimating the abundance of non motile organisms

Answer 5

Methods for estimating the abundance of non-motile organisms include the use of quadrats for making actual counts, measuring population density, percentage cover and percentage frequency.

Question 6

What are direct and indirect methods for estimating the abundance of motile organisms

Answer 6

Direct and indirect methods for estimating the abundance of motile organisms can be described and evaluated. Direct methods include actual counts and sampling. Indirect methods include the use of capture-mark-recapture with the application of the Lincoln Index.

Question 7

Define species richness

Answer 7

Species richness is the number of species in a community and is a useful comparative measure.

Question 8

Define species diversity

Answer 8

Species diversity is a function of the number of species and their relative abundance and can be compared using an index. There are many versions of diversity indices but students are only expected to be able to apply and evaluate the result of the Simpson diversity index. Using its formula, the higher the result, the greater the species diversity. This indication of diversity is only useful when comparing two similar habitats or the same habitat over time.

Question 9

Where should you collect data

Answer 9

• quadrats and transects

Question 10

What should you mesure when collecting data

Answer 10

Measuring abiotic factors
• Marine
• Freshwater
• Terrestrial • Measuring biotics
Biomass and productivity
• Catching small motile animals
• Terrestrial
• Aquatic
• Keys
Measuring abundance
• Lincoln Index
• Simpson diversity index

Question 11

What must you do as you increase number of samples

Answer 11

As you increase the number of samples, plot the number of species found. When this number is stable, you have found all species in the area, so in figure 2.5.3, eight samples are enough.

Question 12

How do you know what quadrant to use

Answer 12

If you increase the size of the quadrat (eg from side length 10 cm to 15 cm, 20 cm and so on) and plot the number of species found, when this number reaches a constant, that is the quadrat size to use.

Question 13

What 2 ways should a quadrat be placed

Answer 13

1. Random quadrats may be placed by throwing the quadrat over your shoulder but we do not recommend this as it could be both dangerous and not random - you may decide where to throw.
   The conventional method (figure 2.5.4) is to use random number tables:
   • Map out your study area.
   • Draw a grid over the study area.
   • Number each square.
   • Use a random number table to identify which squares you need to sample.
2. Stratified random sampling is used when there is an obvious difference within an area to be sampled and two sets of samples are taken.
   This study area (figure 2.5.5) has two distinctly different vegetation types and three separate areas to be studied. Samples need to be taken in each area.
   • Deal with each area separately.
   • Draw a grid for each area.
   • Number the squares in each area (they can be the same numbers or different).
   • Use a random number table to identify which squares you need to sample in each area.

Question 14

Define transect

Answer 14

A transect is a sample path/ line/strip along which you record the occurrence and/ or distribution of plants and animals in a particular study area.

Question 15

When might you use a transect

Answer 15

You might use this to look at changes in organisms as a result of changes along an environmental gradient, eg zonation along a slope, a rocky shore or grassland to woodland, or to measure the change in species composition with increasing distance from a source of pollution. Transects are quick and relatively simple to conduct.

Question 16

What are the 2 main types of transect

Answer 16

1. Line transect: consists of a string or measuring tape which is laid out in the direction of the environmental gradient and species touching the string or tape are recorded.
2. Belt transect: this is a strip of chosen width through the ecosystem.
   It is made by laying two parallel line transects, usually 0.5 or 1 metre apart, between which individuals are sampled.

Question 17

What are the 2 ways transect lines can be

Answer 17

1. In a continuous transect (line or belt transect) the whole line or belt is sampled.
2. In an interrupted transect (line or belt) samples are taken at points along the line or belt. These points are usually taken at regular horizontal or vertical intervals. This is a form of systematic sampling.
   Quadrats are placed at intervals along the belt.

Question 18

What 2 things should you do when measuring abiotic components of a system

Answer 18

1. Describe and evaluate methods for measuring these.
2. Describe and evaluate how to measure spatial and temporal variations in abiotic factors.

Question 19

How can salinity be measured

Answer 19

The salinity can be determined by measuring the electrical conductivity or the density of the water.

Question 20

How can temperature have a significant impact on some organisms

Answer 20

Temperature affects the metabolic rates of marine organisms: this is due to the fact that many are ectothermic (their body temperature is
about the same as the surrounding water). Lower temperatures = low metabolic rates. So changes in temperature caused by thermal pollution may have a significant impact on some organisms.

Question 21

What affects salinity of oxygen in water

Answer 21

• Temperature: higher temperatures = lower concentrations of dissolved oxygen. Many marine organisms rely on dissolved oxygen for respiration hence changes in temperature will impact the marine ecosystem.
• Water pollution: this can cause low oxygen concentrations and thus problems for marine organisms.

Question 22

How can disolved oxygen be measured

Answer 22

Dissolved oxygen can be measured using an oxygen-selective electrode connected to an electronic meter, datalogging, or by a Winkler titration.
(A series of chemicals is added to the water sample and dissolved oxygen in the water reacts with iodide ions to form a golden-brown precipitate.
Acid is then added to release iodine which can be measured, and is proportional to the amount of dissolved oxygen, which can then be calculated.) Oxygen-selective electrodes give quick results, but need to be well maintained and calibrated in order to give accurate results. The Winkler titration is more labour intensive.

Question 23

How does wave action affect an ecosystem

Answer 23

Wave action is important in coastal zones where organisms live close to the water surface. Areas with high wave activity usually have high concentrations of dissolved oxygen. Typical examples are coral reefs and rocky coasts.

Question 24

What is turbidity

Answer 24

High turbidity = cloudy water
Low turbidity = clear water
The turbidity is important because it limits the penetration of sunlight and thereby the depth at which photosynthesis can occur. Turbidity can be measured with optical instruments or by using a Secchi disc.

Question 25

How can turbidity be measured

Answer 25

A Secchi disc is a white or black-and-white disc attached to a graduated rope. The disc is heavy to ensure that the rope goes vertically down. The procedure is:
1. Slowly lower the disc until it disappears from view.
2. Read the depth from the graduated rope.
3. Slowly raise the disc until it is just visible again.
4. Read the depth from the graduated rope.
5. Calculate the average depth. This depth is known as the Secchi depth.
For reliable results a standard procedure should be followed:
• Always stand or always sit in the boat.
• Always wear your glasses or always work without them.
• Always work on the shady side of the boat.
This should be repeated in the same spot 3-5 times.

Question 26

What is flow velocity

Answer 26

This is the speed at which the water is moving and it determines which species can live in a certain area.

Question 27

What 3 things does flow velocity vary with

Answer 27

1. Time: melt water in the spring gives high flow rates, summer drought low flow rates.
2. Depth: Surface water may flow more slowly than that in the middle of the water column.
3. Position in the river: Inside bend has shallow slower-moving water, outside bend has deeper fast-moving water.

Question 28

What are the 3 basic methods for measuring flow velocity

Answer 28

1. Flow meter: These are generally expensive and can be unreliable as mixing water with electricity has its problems.
2. Impellers: a simple mechanical device as shown in figure 2.5.7:
   a. The impeller is mounted on a graduated stick and the base placed on the floor of the river / stream. The height of the impeller can be adiusted and the velocity measured at different depths, BUT it can only be used in clear shallow water, as you must be able to see the impeller.
   b. The impeller is held at the end of the side arm and lowered into the water facing upstream.
   c. The impeller is released and the time it takes to travel the distance of the side arm is measured.
   d. Repeat 3-5 times for accurate results.
3. Floats
   The easiest way to measure flow velocity is to measure the time a floating object takes to travel a certain distance. The floating object should preferably be partly submerged to reduce the effect of the wind. Oranges and grapefruits make suitable floats. This method gives the surface flow velocity only. The average flow velocity of a river can be estimated from the surface flow velocity by dividing the surface velocity by 1.25.

Question 29

What is ph and how can it be measured

Answer 29

pH values of freshwater range from moderately acidic to slightly basic, depending on surrounding soil, rock and vegetation. It can be measured with a pH meter or datalogging pH probe.
For temperature and dissolved oxygen see marine ecosystems

Question 30

What is air temp and how can it be measured

Answer 30

Temperature varies temporally and spatially and can be measured using simple liquid thermometers, min-max thermometers, or more complex (electronic) thermometers. The latter equipment can be used to measure temperature continuously during a longer time as can a data-logging temperature probe.

Question 31

what is light intensity and how should it be measured

Answer 31

This can be measured with electronic meters. The fact that light intensity varies with time (sunny period, clouds, time of the day, season) should be taken into account.

Question 32

How should you measure wind speed

Answer 32

A revolving cup anemometer consists of three cups that rotate in the wind. The number of rotations per time period is counted and converted to a wind speed. Revolving cup anemometers can be mounted permanently or hand-held.
• A ventimeter is a calibrated tube over which the wind passes. This reduces the pressure in the tube, which makes a pointer move. It is easy to use and inexpensive.
• By observation of the effect of the wind on objects. The observations are then related to the Beaufort Scale (a scale of wind speed from 0 to 12).

Question 33

How can rainfall be collected

Answer 33

Rainfall can be collected using a rain gauge. Some schools have an established weather station - in which case collecting rainfall data is easy.
Many schools will not have a weather station but rain gauges are very easy to make and there are plenty of websites that can give you advice on how to make your own. Once you have made your rain gauge:
1. Place your rain gauge in a suitable spot in the study area - somewhere away from the influence of buildings, trees and other obstacles that may affect rainfall.
2. Check rain gauge every 24 hours - at the same time every day. Pour rain into a graduated cylinder and record daily amount of rainfall.

Question 34

LOOK AT TABLE ON 133 ON HOW TO MEASURE SOIL

Question 35

How can you measure soil moisture

Answer 35

This is the amount of water in the soil. It can be measured by drying soil samples.
1. Place a sample of the soil in a crucible.
2. Weigh it and record the weight.
3. Dry the sample.
Drying can be done in a conventional drying oven or a microwave oven.
In a conventional oven:
• Set the oven to 105 °C; hot enough to dry the soil but not so hot as to burn off organic matter.
• Leave for 24 hours and weigh the sample, repeat this until its mass becomes constant. This takes several days. In a microwave oven:
• Place the sample in the microwave for 10 minutes.
• Weigh the sample, and return to the oven for 5 minutes - repeat until its mass becomes constant.
A minimum of 3-5 samples should be tested.

Question 36

What are the serval functions of the organic content of soil.

Answer 36

• Supplies nutrients to the soil.
• Holds water (like a sponge).
• Helps reduce compaction and crusting.
• Increases infiltration.

Question 37

How can the organic content be determined

Answer 37

Organic content can be determined by the loss on ignition (LOI) method.
1. Dry the sample as above.
2. Heat the soil at high temperatures of 500 to 1,000 °C for several hours.
3. Weigh the sample and repeat this until its mass becomes constant.

Question 38

How do you measure the mineral content and ph levels in soil

Answer 38

Mineral content and pH
There is a wide range of soil nutrients essential for a fertile soil. These are easy to measure through traditional soil testing kits or the ones available in many gardening centres.
Soil pH can also be measured using a soil testing kit or a pH probe.

Question 39

What questions do we need to observe when measuring biotic content

Answer 39

• Why is it as it is?
• What has changed recently?
• Why does this grow here and not there?
• What impact do more people walking here have?
So walk around your institution’s grounds or the local

Question 40

How do you measure biomass and productivity for low vegetation and grasses

Answer 40

1. Place a suitably sized quadrat (see figure 2.5.2).
2. Harvest all the above-ground vegetation in that area.
3. Wash it to remove any insects.
4. Dry it at about 60-70°C until it reaches a constant weight. Water content can vary enormously so all the water should be removed and the mass given as dry weight.
5. For accurate results this should be repeated 3-5 times so that a mean per unit area can be obtained.
6. The result can then be extrapolated to the total biomass of that species in the ecosystem.

Question 41

How do you measure the biomass and productivity of trees and bushes

Answer 41

1. Select the tree or bush you which to test.
2. Harvest the leaves from 3-5 branches.
3. And repeat steps 3-6 in the above method.

Question 42

How do you measure productivity in a aquatic ecosystem

Answer 42

1. Take two bottles filled with water from the ecosystem.
   a. One of the bottles is made of clear glass.
   b. The other is of dark glass or is covered to exclude light.
2. Measure the oxygen concentration of the water by chemical titration
   (Winkler method) or an oxygen probe, and record it as mg oxygen per litre of water.
3. Place equal amounts of plants of the same species into each of the bottles.
4. Both bottles must be completely filled with water and capped. (No air should be present.)
5. Allow to stand and incubate for several hours.
6. Measure the oxygen levels in both bottles and compare with the original oxygen level of the water. The incubation can take place in the laboratory or outdoors in the ecosystem of investigation.

Question 43

How do you measure productivity in a terrestrial ecosystem

Answer 43

1. Select three equally sized patches with similar vegetation (eg grass).
2. The first patch (A) is harvested immediately and the biomass measured (see above).
3. The second patch (B) is covered with black plastic (no photosynthesis, just respiration).
4. The third patch (C) is just left as it is.
5. After a suitable time period (depends on the season), patches B and
   C are harvested and the biomass measured (as above).
6. Now GPP, NPP and R can be calculated (usually per m?).

Question 44

What is a typical secondary productivity experiment

Answer 44

In a typical experiment, a herbivore is fed with a known amount of food. The procedure is that the food and the herbivore(s) are weighed. After a suitable time period, the remaining food, the herbivore(s) and the feces are weighed.

Question 45

What is a pitfall trap

Answer 45

The pitfall trap is ideal for catching insects and other small crawling animals that cannot fly away (see figure 2.5.10). Insects can be attracted by decaying meat or sweet sugar solution (this must be covered so the insects do not fall in it and drown) and will fall into the trap.Several of these traps can be placed around the study area. They should be checked at regular intervals (every 6 hours) and the species and number of that species recorded.

Question 46

What are sweep nets

Answer 46

Sweep nets of various sizes can be swept through grasses at various heights in order to catch many insects.
These can then be emptied into a large clear container and the species and numbers recorded.

Question 47

What is tree beating

Answer 47

This method can find insects in tree branches. Simply place a catching tray beneath a tree branch and gently tap the branch. The tray will catch anything that falls from the tree and you can log the species and their numbers. Night-flying moths will be attracted to a light behind which a white sheet is hung and the moths settle on this for you to observe.Small insects and invertebrates can be caught with a pooter - a small jar with two tubes attached (see figure 2.5.13). You suck gently on one tube and the animal is pulled into the jar. You cannot swallow it as there is gauze at the end of the mouthpiece tube!

Question 48

What is kick sampling

Answer 48

The organisms of most interest will be the stream invertebrates and the most efficient way to catch them is through kick samples.
Kick sampling is another simple technique:
• Place the sweep net downstream from you.
• Shuffle your feet into the streambed for 30 seconds.
• Empty the contents of the net into a tray filled with stream water.
• Use a pipette to sort the various insects into small plastic cups and record your results.
• Repeat three times to ensure good results.
In aquatic systems, nets of various mesh sizes and net sizes can be used to catch plankton, small invertebrates or larger fish. These can be towed behind boats or held in running water. Simple plastic sieves are effective. Kick sampling loosens invertebrates, which drift into the net. Turning stones over is also effective. Some of these methods are destructive and kill the organisms.
You may think this is not acceptable but most do not harm the organisms caught and you should always return them to their habitats if at all possible.

Question 49

What is a key

Answer 49

Once you have collected the organisms, you may want to find out what they are called. A (biological) key is used to identify species. Ecologists make keys to specific groups of organisms, eg soil invertebrates in specific ecosystems, to help other interested people identify species. Keys come in two formats, a diagrammatic, dichotomous or ‘spider’ key and a paired statement key.
Look at examples of published keys. Diagram keys are useful but professionals use paired statement keys because printed descriptions are more exact than pictures. Both keys are used by starting at the top each time and following the lines or ‘go to’ numbers.

Question 50

How do you measure abundance

Answer 50

There are a number of ways of assessing plant species abundance:
• Density: mean number of plants per m?.
• Frequency: the percentage of the total quadrat number that the species was present in, may also be measured within the quadrat.
• Percentage cover: because plants spread out and grow percentage cover is often measured instead of individual numbers. This is an estimate of the coverage by each species and it sometimes helps if the quadrat is divided up for this. Species may overlap or lie in different storeys in a forest, so the percentage cover within a quadrat may be well over 100% or much less if there is bare ground. The percentage cover can be estimated either by comparing the sample area with figure 2.5.16 and then it can be graded on a scale from 0 to 5, or on the ACFOR scale by using figure 2.5.17.

Question 51

What is the Lincoln index

Answer 51

Capture, mark, release recapture

Question 52

How is the Lincoln index taken out

Answer 52

1. Establish the study area.
2. Capture a sample of the population. The actual method of capture will depend on the size of animals; you can take your pick from the methods discussed earlier.
3. Mark each of the organisms captured and record how many you have marked: this must be done in a non-harmful way that does not expose them to higher predation levels than non-marked individuals.
   For example, dog whelks on a rocky shore or woodlice in a woodland can be marked with a spot of non-toxic subtle coloured paint (nothing bright).
4. Release the captured individuals back into the environment and allow sufficient time to remix with the population.
5. Take a second sample in the same way as the first: count the number of organisms captured in this sample and count how many of them are marked. At least 10% of the marked sample should be recaptured if this estimate is going to be fairly accurate.

Question 53

What assumptions should be made when carrying out the Lincoln index

Answer 53

• Mixing is complete, ie the marked individuals have spread throughout the population.
• Marks do not disappear.
• Marks are not harmful nor increase predation by making the individual more easily seen.
• It is equally easy to catch every individual.
• There are no immigration, emigration, births or deaths in the population between the times of sampling.
• Trapping the organisms does not affect their chances of being trapped a second time.

Question 54

State the Lincoln index formula

Answer 54

M2/n2 = n1/N

N= n1xn2/ms
Where
n1= number of animals first marked and released
n2= number of animals captured in the second sample
m2= number of marked animals in the second sample
N = Lincoln Index or total population (the figure you are after)

Question 55

Define species diversity

Answer 55

Species diversity is a function of the number of species and their relative abundance.

Question 56

What is the Simpson’s diversity index

Answer 56

Ecologists try to express diversity in a number. The higher the number, the greater the species diversity. This makes it possible to compare similar ecosystems or to see whether ecosystems are changing in time. The most common way to turn diversity into a number is by the Simpson diversity index.

Question 57

What does the Simpson’s diversity index describe

Answer 57

But be careful. The name ‘Simpson diversity index’ actually describes three related indices (Simpson’s Index, Simpson’s index of diversity and Simpson’s reciprocal index). Here we are using Simpson’s reciprocal index in which 1 is the lowest value (when there would be just one species) and a higher value means more diversity. The highest value is equal to the number of species in the sample. In the other indices, the value ranges from 0 to 1.

Question 58

State the Simpson’s diversity formula

Answer 58

D=n(n-1)/sigma N (n-1)

D = Simpson diversity index
N = total number of organisms of all species found
n = number of individuals of a particular species

Question 59

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