random sampling

Question 1

list 3 ways that you can make a sample representative

Answer 1

• random sampling
  (in a uniform area to eliminate bias)
• line transects to examine a change over distance
• large number of samples

Question 2

what is random sampling used to estimate

Answer 2

population sizes that are evenly distributed

Question 3

explain the procedure of random sampling
(4 marks)

Answer 3

• line 2 tape measures at right angles to create a gridded area
• use random number generator to generate 2 coordinates
• place the quadrat and collect the data (density, percentage cover, frequency)
• repeat at least 30 times and calculate a mean

Question 4

what are line transects used to estimate

Answer 4

a population size when they are unevenly distributed

(e.g: populations that change over a distance)

Question 5

name one example when you would use a line transect

Answer 5

sandy/rocky shores

across a path or river

Question 6

name the 2 types of transects

Answer 6

belt transect

interrupted belt transect

Question 7

explain what a belt transect is

Answer 7

quadrat is placed at every position along the tape measure

Question 8

explain what a interrupted belt transect is

Answer 8

the quadrat is placed at uniform intervals along the tape measure

(e.g: every 5 metres)

Question 9

explain the procedure of doing a interrupted belt transect over a shoreline
(4 marks)

Answer 9

• place the tape measure at a right angle to the shoreline
• place the quadrat every 5 metres
• collect the data
  (density, percentage cover, local frequency)
• repeat by placing 30 transects along the beach at right angles to the shoreline

Question 10

what are the 3 methods to estimate the abundance of a species

Answer 10

1. local frequency
2. density
3. percentage cover

Question 11

define local frequency

Answer 11

the percentage of the squares in the quadrat with the species present

Question 12

define density in terms of estimating the abundance of a species

Answer 12

the number of one species in a given area

Question 13

define percentage cover

Answer 13

proportion of the ground occupied by the species

Question 14

how do you calculate density

Answer 14

number of species times area of whole field/area of quadrat

Question 15

how do calculate percentage cover

Answer 15

amount of full squares covered

Question 16

evaluate local frequency

Answer 16

+ quick method to sample a large area
+ useful if too difficult to identify as individual organism
- poor accuracy as doesn’t consider overlapping plants or the size of the plant

Question 17

evaluate density

Answer 17

+ more accurate if you can easily distinguish an individual plant and there aren’t too many to count
+ used to estimate species richness (number of different species)
- time consuming

Question 18

evaluate percentage cover

Answer 18

+ quicker method than density
+ useful if it is to identify individual organism
- subjective limiting accuracy
- doesn’t consider overlapping plants or size of plant