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What is a quadrat?
A sample area in a habitat allowing the organisms within it to be counted
What are quadrats useful for?
Comparing the numbers of a species in one area with those of another
How is ensured that the sampling area is representative?
- A large number of quadrats are used
- Larger quadrats
How is ensured that the sampling area is non biased?
- The quadrats are placed randomly
- A grid map of the area is made
- A calculator is used to generate random numbers to act as co-ordinates
In which two ways can quadrat data be recorded?
- Counting the number of specimens of each species in the quadrat and dividing the number of organisms by the area of ground sampled to find population density
- Estimating the percentage cover of the quadrat that is covered by a particular species
What is a transect?
A line marked with tape or strain through a habitat along which organisms are sampled
When are transects used?
When studying an area where there is a gradual change from one set of conditions to another (organisms from the sea shore to the climax)
How are results recorded on a standard line transect?
All plants that touch the linePlants touching at regular intervals (10cm)
What is a belt transect?
A transect along which quadrats are placed at regular intervals
How can bias be avoided when using transacts?
The species are recorded from several randomly placed transects across the area
What should also be recorded along with transect data?
The physical features of the environment along the transect such as the height across a rocky shore
What does the accuracy of a quadrat depend on?
The size of the quadrat and the number of repetitions made
How is the the accuracy of a quadrat limited?
Effectiveness is limited if the species do not grow as individuals
In what circumstanced can quadrats not be used?
On uneven ground
When can vegetation prevent the usage of a quadrat?
When it is too tall
What type of organisms can be measured by a qadrat or transect?
Plants or stationary animals (molluscs)
What is netting used for?
To sample animals that move and cannot be sampled using quadrats
How must netting be carried out?
In a standard way to avoid variation in technique
What is trapping used to sample?
Larger and more mobile organisms
State two examples of trap sampling techniques
- Longworth traps for small mammals
- Pitfall traps for non flying insects and other invertebrates
What is mark, release, recapture used for?
To estimate the size of a population of mobile animals
How is a representative mark, release, recapture sample ensured?
A large number of the desired sampling animal is captured
What must be ensured when animals are marked and released?
- The marking must be non toxic
- Must not make the animal stand out to predators
Describe the mark, release, recapture process.
- First group is captured, counted and marked then released
- The second group is captured, the number of marked and the total number are counted
- The lincoln index is used to calculate population size
How do you calculate the Lincoln index?
Number in sample 1 X number in sample 2 divided by number of marked animals in sample 2
What must be assumed during mark, capture, release?
- The marked creatures mix randomly in the population
- There is no migration or immigration, births or deaths