Investigating Population Size Flashcards
Which technique is used to investigate the population size of non-motile organisms?
Quadrat
Which technique is used to investigate population size of slow moving organisms?
Transect
What does species frequency record?
The proportion of quadrats in which you find a particular species.
How do you calculate the number of organisms per unit area?
- calculate mean number of organisms
- divide mean number by area of quadrat.
When is percentage cover used and how is it recorded?
- used when plants are too small to count individually (grass)
- count the number of squares occupied by a species, then calculate this as a percentage of the whole quadrat area.
How many quadrats should be used in an ecology investigation?
Atleast 20 quadrats so that:
- mean result will be more representative
- mean result will be more reliable as the effect of outliers is reduced
- generates enough data to allow a statistical test to be carried out.
What is the importance of random sampling?
Random sampling removes investigator bias which means that the investigator hasn’t influenced the results.
Describe how you could estimate the number of bluebells in a small woodland.
- Divide the study area into a grid using two tape measures
- Obtains 20 pairs of coordinates using a random number generator
- For each pair of coordinates, find the sample point in the grid, place the quadrat on the ground and count the number of bluebells in the quadrat
- Calculate the mean number of bluebells in the sample grid and divide by the area of the quadrat then multiply by the area of the whole study area
Describe how you would investigate the distribution of marram grass from one side of the dune to the other.
- Use a transect from one side of the dune to the other
- Place the quadrats at regular intervals along a line
- Calculate percentage cover of marram grass
- Repeat up to 20 times along the dune
How is mark-release-recapture used to estimate the size of a motile animal population?
- Catch a sample and count the number of individuals if the sample you wish to study
- Mark each animal in a way that will not harm them or attract predators
- Release the marked animals back into their habitat and allow enough time for them to evenly distribute into the population
- Catch a second sample and count the total number of individuals caught and count the number which are marked
- (Total number in sample 1 X total number in sample 2) / total marked in sample 2
When is the estimated population size of motile organisms reliable?
- sample numbers caught are large
- populations number doesn’t change significantly
- marked animals have the same survival chance as unmarked animals
- marked animals distribute evenly into the population when rereleased
