11.2 Sampling

Question 1

What is sampling?

Answer 1

Taking measurements of a limited number of individual organisms present in a particular area

Question 2

What can sampling be used for?

Answer 2

Estimating the number of organisms in an area without having to count them

Question 3

What is abundance of an organism?

Answer 3

Number of individuals of a species present in an area

Question 4

What else can sampling be used for?

Answer 4

Measuring a particular characteristic of an organism
Example:
You can’t reliably determine the height of wheat by measuring one wheat plant in a field. However, if you measure the height of many plants and calculate a mean, the result will be closer to the average height of the entire crop

Question 5

What can you do with sample results?

Answer 5

Make generalizations or estimates about the number of organisms, distribution of species or measured characteristics throughout the entire habitat

Question 6

What are the two types of sampling?

Answer 6

1. Random

2. Non-random

Question 7

What is random sampling?

Answer 7

Selecting individuals by chance

-Each individual has the same chance of being selected

Question 8

How do you decide a random sample?

Answer 8

Use random number tables or computers

Question 9

For example, how would you take a random sample of a grass verge?

Answer 9

1. Mark out a grid on the grass using two tape measures laid at right angles
2. Use random numbers to determine the x and y coordinate on your grid
3. Take a sample at each coordinate

Question 10

What is non-random sampling?

Answer 10

Sample is not chosen at random

Question 11

What are the 3 techniques of non-random sampling? define them

Answer 11

• Weakest form of sampling as it may not represent the whole population
• Uses any organisms that are available

Question 12

What is stratified sampling?

Answer 12

-Some populations can be divided into a number of strata (sub-groups) based on a certain characteristic
For example:
Population separated into males and females
A random sample is taken from each of these strata proportional to its size

Question 13

What is systematic sampling?

Answer 13

Different areas within a habitat are identified which are then sampled independently
For example:
Systematic sampling can be used to study how plant species change as you move inland from the sea
-Often carried out using a line or belt transect

Line transect - mark a line along the ground between 2 poles and taking samples at specified points
i.e. describing all organisms which touch the line/distances of samples from the line

Belt transect - Provides more info; 2 parallel lines are marked and samples are taken from the area between the 2 lines