2.7 Measuring changes in the system

2.7 Measuring changes in the
Describe and evaluate methods for measuring change along an
environmental gradient
What is an ecological gradient? Changes in the abiotic and biotic factors of an
environment over space or time. It occurs when one ecosystem meets another
e.g. a beach turning into sanddnues.
T / F : Biotic and abiotic factors will change with distance along an ecological gradient.
In ecology and geography what is a transect? The act of travelling within a path and
record the occurrence of a certain phenomena
Why is a transect good to use to show changes along an ecological gradient? Because it
shows a numerical value of data per unit of distance.
What is a line transect?
When you record the plants or animals touching /close to a line at set intervals.
What is a belt transect?
When you use a quadrat to record the plants/animals along a line. A wider area is measured.
What is a continuous transect?
When you record the plants/animals (with or without a quadrat) along a line with no gaps.
What is an interrupted transect?
When you record the plants/animals (with or without a quadrat) along a line at set intervals e.g. every 5
What limitations would you encounter if you carried out your transect readings at different times of the year?
Or even of the day?
Certain times of the year, or the day, are more active than others. For example, some animals may only
come out at night because they are nocturnal, and some animals hibernate or change location for the
winter months. Plants will grow as time goes by, or die.
How many times should you repeat transect readings to make sure they are reliable?
3 is recommended. As many times as possible – the more trials, the more accurate they will be.
How can you avoid bias in where you put your transect?
You could turn your back and toss the quadrat, so that it would not be possible to be biased in choosing a
location. Mark out an area with numbers and then use random numbers to generate the area where you
What is random sampling with quadrats?
Taking a quadrat upon an area of study and throw it at a given direction. Record the variable
used in the study and then throw it again but in a different direction away from the previous
What is stratified random sampling?
A method of sampling which takes into account separate/individual areas within a given
habitat e.g. if an area is half sand and half sand-dune you would make you 50% of your
readings came from each area.
What is systematic sampling?
A sample selected by a systematic method; for example, units selected from a list at equally
spaced intervals after a random start or every 2 metres or every 10th person
What is percentage cover when measuring abundance?
It is the estimate of the area a species covers in a quadrat, so if you have 100 little squares in
1 quadrat, then you count the squares in which the plant species is present = you count a
square only when it is half or more covered by the plant. So if the plant is in about 25 squares
within the quadrat you can say the plant covers 25% of the area.
What is intensive agriculture?
Intensive farming practices include growing high-yield crops, using fertilisers and pesticides and
keeping animals indoors. Food production is increased but there are unwelcome side effects.
Machinery such as tractors use diesel which can be leaked into the stream and kill the animal and
plant life within the water.
Fertilisers will be absorbed into the ground-water, which will then flow into the stream and cause
rapid growth of surface algae, which will, ultimately, result in the blocking of sunlight into the
stream. This will lead to the eradication of algae and organisms in the stream, and it will cause the
water to become anoxic (deoxygenated.)
Pesticides will result in the elimination of several essential species, as well as the ones targeted by
the pesticides, as well as increasing the acidity of the water.
Eutrophication: a process where water bodies receive excess nutrients that stimulate excessive plant
Algae: Rapid growth followed by eventual death due to lack of fish.
Other plants: Grow at first and then rapid growth of algae eventually restricts sunlight from reaching
the other plant-life in the stream, and thus, they die out.
Fish: The dying out of the other plants in the stream means that no more oxygen is being produced and
decomposers use up the oxygen that is available , making the stream anoxic, resulting in fish dying
So, you need to be able to describe and evaluate methods for measuring changes in
abiotic and biotic components of an ecosystem due to a specific human activity. (2.7.2)
i.e. say how the pollution from the farm is affecting the stream
If one farm was causing the pollution to the nearby stream mark on two places where you would
do your tests (indicated by the red dots, before and after the farm) .
How would you test for fertilizers/pesticides?
Use a water test kit to test the phosphate and nitrate levels in the stream, which would indicate the
contamination of the water by the fertilizers and pesticides. Tests would be done before and after
the farm (locations indicated by the red dots above) in order to access and be able to compare the
affected and unaffected areas.
How would you test for biotic factors (animal and plant life)?
Do a quantity test with a net – hold the net against the current for a fixed amount of time and once
the time is up, count the number of organisms in the net. For plants, quadrat. Repeat for both
locations to access the changes.
Possible IB question:
Describe and evaluate methods for measuring changes in abiotic
and biotic components of an ecosystem due to a specific human
. (6)
What are they?
a systematic process to identify, predict and evaluate the environmental effects of proposed actions in
order to aid decision making regarding the significant environmental consequences of projects,
developments and programmes. It highlights possible advantages and disadvantages of projects and
offers alternatives. It aims to cover social, economic and environmental impacts.
What is a baseline study?
A study before any development has taken place that aims to (i) assess present environmental quality
and the environmental impacts and (ii) identify environmentally significant factors that could
preclude project development.
What are the + and – of EIAs?
EIA often focuses on biophysical issues (often a fault of poor terms of reference);
• Where environment, social and economic aspects are addressed, they are not always addressed in an
integrated way (EIA reports tend to present as separate chapters)
• EIA provides an opportunity to learn from experience of similar projects and avoids the (often high)
costs of subsequently mitigating unforeseen negative and damaging impacts.
• EIA Improves long-term viability of many projects
• Offers alternative projects which may have more positive outcomes
• Depends who does the EIA and if they have any involvement with company

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