4.2.1 random and non-random sampling

Question 1

what is sampling?

Answer 1

measuring a limited number of individual organisms present in an area and using the results to estimate the population size

Question 2

what can sampling be used to do?

Answer 2

1. estimate the number of organisms in an area without having to count them all
2. measure a particular characteristic of an organism

Question 3

what is the abundance of the organisms?

Answer 3

number of individuals species present in an area at a given time

Question 4

what is random sampling?

Answer 4

selecting individuals by chance so each individual in the population has a likelihood of being selected

Question 5

what can the abundance of an organism vary due to?

Answer 5

births, deaths, immigration, emigration

Question 6

what is distribution of a species?

Answer 6

where individual organisms are found within a given area/ ecosystem

Question 7

when is random sampling used?

Answer 7

1. when you want a representative sample of the WHOLE AREA
2. when there is no reason to believe that there is a pattern to the way that the organisms are distributed

Question 8

how would you take a random sample from a grass verge to see what species are growing there?

Answer 8

1. mark out the area of study with 2 tape measures at right angles
2. use a random number generator to pick 2 co-ordinates ( x and y)
3. take sample of each of the co-ordinate pairs generated
4. repeat to take 10 samples

Question 9

what is an advantage of random sampling?

Answer 9

avoids bias, otherwise scientist might sample areas because they look interesting

Question 10

what is a disadvantage of random sampling?

Answer 10

it may not cover all the areas of the habitat equally so species present in small numbers could be missed, giving an underestimate of the biodiversity

Question 11

what is non-random sampling?

Answer 11

where the sample is not chose by chance

Question 12

when is non-random sampling used?

Answer 12

when you suspect there is a specific pattern in the way organisms are distributed in a ecosystem

Question 13

what are the 3 different types of non-random sampling?

Answer 13

1. opportunistic
2. stratified
3. systematic

Question 14

what is opportunistic sampling?

Answer 14

the researcher deliberately samples an area where they can see a particular species of interest is present

Question 15

what is an advantage of opportunistic sampling?

Answer 15

it is easier and quicker than random sampling

Question 16

what is a disadvantage of opportunistic sampling?

Answer 16

data is biased as it may lead to an overestimate of a particular species in an area

Question 17

what is stratified sampling?

Answer 17

dividing a habitat into areas that appear different and sampling each area separately

Question 18

advantage of stratified sampling

Answer 18

ensures all areas of a habitat are sampled (random sampling might miss areas)

Question 19

disadvantage of stratified sampling

Answer 19

can lead to over representation and under representation of species

Question 20

what is systematic sampling?

Answer 20

samples are taken at fixed intervals across a habitat - transect
(most common form of non-random)

Question 21

advantage of systematic sampling

Answer 21

useful in a habitat that shows a clear gradient in an environmental factor
(eg as you move away from the pond the land dries out)