2.5 Investigating ecosystems Flashcards
What are the three types of sampling?
- Random sampling
- Systemic samplig
- Stratified sampling
Random sampling- how biased is it? + outline methodology
- This technique does not involve any subjectivity and is thus theleast biased method
- Random sampling of an area: make a grid to identify sampling locations, must be chosen randomly
Advantages and disadvantages of random sampling?
Advantages:
- Unbiased
- Suitable for large populations
Disadvantages:
- You may not have access to some of the sample points.
- In large study areas the sample points may miss some places
Explain a bit systematic sampling
- Often referred to as the nth method:
- Every 5thperson that passes you
- Every meter along a transect line
- Samples every 30 minutes through the day
(Fatima lo usaste para tu IA acuerdate csm)
Advantages and disadvantages of systematic sampling
Advantages:
- Easier to apply that random sampling –> No need to use a grid
- Coverage of the whole study area can be achieved (random sampling does not do this)
Disadvantages:
- May be biased because places have a different chance of selection.
- Patterns may be missed or areas exaggerated.
When is stratified sampling used?
This technique is used when the population is known to contain subsets.
What are the types of stratified sampling? (HINT: Se mix con los otros dos types de sampling)
- Stratified systematic sampling: every 5th student of every year group (strata)
- Stratified random sampling: random students from every year group
Advantages and disadvantages of stratified sampling
Advantages:
- Flexible – can be used in many situations as it combines with random and systematic.
- Good for comparing subsets
Disadvantages:
- You must know the size of the subsets to get an accurate picture.
When are quadrats used? (for what type of organism) (Hint 3 points)
- To study plants and non-motile animals or ones that do not move very much
- To see percentage frequency: how often a particular species appears in an area
- To see population density
Advantages and disadvantages of quadrats (Hint: 3 each)
Advantages:
- Quick easy method to apply.
- Accurate with large species
- Good for comparisons over time or space.
Disadvantages:
- Very difficult with small species
- May miss some species in layered vegetation.
- Species may look different in different life stages
Advantages and disadvantages of quadrats SPECIFICALLY for assessing percentage cover
Adavantages:
- Avoids some of the problems of counting individuals
- Good for comparisons over time or space
Disadvantages:
- Difficult to assess accurately in layered vegetation
- Must be able to identify species accurately
- Coverage can exceed 100% if the vegetation is layered
What are the 3 methods to evaluate abiotic factors?
- Probes
- Sechi disk
- Anemometer
Probes— what abiotic factor(s) can they measure
Salinity, pH, temperature, dissolved oxygen, light intensity and soil moisture and mineral content
Evaluate advantages and disadvantages of PRObes
Advantages:
- Quick, easy to use, accurrate
- When attached to a datalogger they can take continuous readings over a period of time
Disadvantages:
- May be expensive
- May not be available in all countries
secchi disk— what abioitic factor does it measure, how do you use it
- turbidity
- It is lowered into the water of a lake until it can no longer be seen by the observer. This depth of disappearance, called the Secchi depth, is a measure of the transparency of the water.
Advantages and disadvantages of secchi disk
Advantages:
- Simple instrument - no mechanics to go wrong.
- Easy to make one for yourself (DIYY)
- Cheap
Disadvantages:
- Need a boat or a dock to get into deep enough water to lower the disk.
- Different people may have different abilities to see the disk: prone to human error
What does the anemometer measure?
It measures windspeed
Advantages and disadvantages of the anemometer (HINT: mismos disadvantages de PRObe)
Advantages:
- Gives an immediate reading with no calculations needed
- Quick results
- Simple to use
Disadvantages:
- May be expensive
- May not be available in some countries
What are the basic rules to building a dichotomous key?
- observable characteristics
- Give specific measurements if you are talking about size or weight
Beware of using colour as some organisms change colour during the year
How to measure primary productivity (NPP and GPP)- verbal explanation
(remember NPP= GPP-R)
3 identical quadrats, same size, same vegetation
- Quadrat B is covered in a plastic sheet, that means that the vegetation will not photosynthesise, just respire
- Then, to find the NPP, harvest all biomass in quadrat A before the experiment begins, dry it, weigh it, and find the biomass
- after a month of however long the experiment goes, harvest quadrat C
- NPP= Quadrat C biomass- Quadrat A biomass
- now that you have the NPP you can find the GPP
- NPP=GPP-R
- you have R from Quadrat B and NPP from Quadrat C and A therefore finding the GPP is a matter of rearranging the equation to make GPP the subject
- Te lo vas a tener que paporretear*
How to measure secondary productivity- verbal explanation of method
- remember:
- GSP= food eaten-feacal loss
- NSP= GSP-R
- Method: - estimate GSP by knowing the weight of the food eaten and the weight of fecal losses.
- weight of food- weight of fecal losses = GSP
- estimate NSP by knowing the weight of the organism at the start and the end of the investigation and respiration can be extrapolated
- weight of organism at end of experiment- weight of organism at the beggining
- find the GSP, NSP and respiratory losses
- weight of organism at end of experiment- weight of organism at the beggining
Exercise:
- find the GSP, NSP and respiratory losses from the following information:
- 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 losses
–> GSP= 5-4, GSP=1
–> NSP= weight at end - weight at beggining
- 3.5 - 3.0
NSP=0.5
–> NSP= GSP-R
- 0.5- 1-R
- R= 0.5
How to investigate motile organisms? (methods) (Acuerdate, motile = mobile) (HINT: Listalos son 4)
- Kick sampling
- Pitfall traps
- Aerial photography
- mark/release/recapture method
Kick sampling (outline method + for what species of organism would we use this method)
- For stream invertebrates (fishies)
- The person with the net stands downstream making sure the net is touching the bottom of the stream.
- 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.
- eventually release them
Pitfall traps (outline method + for what species of organism would we use this method) (HINT: El container es como un hotelito par alos insectos)
- Designed to captureground dwelling insects
- Lid supported by a few rocks to keep rain and sun out
- Top of the ocntainer should be just below ground level
- Container to hold the organism should have food and bedding in
Aerial photography- advantages and disadvantages
Advantages:
-Can be used to study large areas
- Can be used on large animals
- Can be use don carnivores
Disadvantages:
- Very expensive
- Animals may move and appear in 2 squares
- Animals may be hidden by trees
Mark/release/recapture method (Lincon index)- explain the method
- Capture the organism using any method
- Mark the organisms in some way that does not harm them or make them more or less prone to predation.
- Record the number of animals that were caught and marked.
- Release the animals back into their environment and give them sufficient time to reintegrate into the population (oneweek toa month).
- Resample the population and record the number of animals that are marked and unmarked.
- Use the following formula to calculate the total population:
- N = n1 × n2 / m2
- 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).
- N = n1 × n2 / m2
What is the formula when calculating the total population with the Mark/release/recapture?
- N = n1 × n2 / m2
- 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).
what are the problems with the Mark/release/recapture method??
- Capturing the animals 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.
