B7 Using Quadrats (page 87) Flashcards
After reading page 83, you know a habitat is the place where organiss lives, give an example?
e.g. playing field.
(organisms live in different places because the environment varies).
What is meant by the distribution of an organism?
it is where an organism is found, e.g. in a part of the playing field.
Where an organism is found is affected by environmental factors (see page 84)
An organism might be more common in one area than another due to differences in environmental factors between the two areas, give example?
e.g. in the playing field, you might find that daisies are more common in the open than uder trees, because there’s more light available in the open.
What are the two ways to study the distribution of an organism?
you can:
measure how common an organism is in two sample areas (using quadrats) and compare them.
study how the distribution changes across an area, e.g. by placing quadrats along a transect (pg 88).
Both these methods give quantitative date (numbers) about the distribution.
What can you use to study the distribution of small organisms?
Quadrats.
What is a Quadrat?
it is a square frame enclosing a known area
e.g. 1m²
This is to compare how common an organism is in two sample areas (e.g. shady and sunny spots in that playing field.
How do you use a Quadrat?
1) place a 1m² quadrat on the ground at a random point within the first sample area. (e.g. divide the area into a grid and use a random number generator to pick coordinates).
2) Count all the organisms within the quadrat
3) Repeat steps 1 and 2 as many times as you can.
4) Work out the mean number of organisms per quadrat within the first sample area
(look at example to work out mean on page 87)
5) Repeat steps 1 to 4 in the second sample area.
6) Finally compare the two means. E.g. you might find 2 daisies per m² in the shade, and 22 daisies per m² (lots more) in the open field.
You can also work out the population size of an organism in one area, give answer?
Students used quadrats, each with an area of 0.5 m², to randomly sample daisies on an open field. The students found a mean of 10.5 daisies per quadrat. The field had an area of 800m². Estimate the population of daisies on the field?
1) work out the mean number of organisms per m²
1 ÷ 0.5 = 2
2 x 10.5 = 21 daisies per m²
2) Then multiply the mean by the total area (in m²) of the habitat
800 x 21 = 16,800 of daisies on the open field
The population size of an organism is sometimes called what?
its abundance
If your quadrat has an area of 1m², the mean number of organisms per m² is what?
is just the same as the mean number per quadrat.
A 1200m² field was randomly samples for buttercups using a quadrat with an area of 0.25m². A mean of 0.75 buttercups were found per quadrat.
Estimate the total population of buttercups? (2 marks)
0.75 x 4 = 3 buttercups per m² (1 mark)
3 x 1200 = 3600 buttercups in total (1 mark)
