Ecosystems - Sampling Methods

Question 1

define abundance

Answer 1

how many organisms are present (number/percentage cover/ACFOR scale)

Question 2

define distribution

Answer 2

where in the ecosystem the organism is

Question 3

what are the different types of distribution

Answer 3

• uniform
• clumped
• random

Question 4

why are sampling techniques used

Answer 4

• studying every organism in an ecosystem is too time consuming
• samples can be used to estimate the number of organisms in a habitat or to measure characteristics of the organisms in the habitat

Question 5

why are random samples used

Answer 5

to avoid bias

Question 6

describe how you decide where to place your quadrat in a given area

Answer 6

• use a random number generator to generate coordinates
• use these on axes made using a tape measurer or laser pointer
• place bottom left hand corner of quadrat on coordinate
• repeat until you have samples 10% of the area or until cumulative frequency is no longer changing

Question 7

what are the limitations of this method of using quadrats and how could you modify it

Answer 7

• researcher chooses area so may be biased –> do repeats in different areas
• seasonal variation –> repeat at different times of year
• difficulty identifying species –> consult expert
• may not find grid reference correctly –> use two tape measurers or lasers

Question 8

how could you reduce the effect of chance meaning that your sample is not representative of that area

Answer 8

repeat with more quadrats in more areas

Question 9

why may non-random sampling methods be useful

Answer 9

to ensure all areas of a habitat where there is a lot of variation are studied and to look at the distribution of organisms

Question 10

what are the three types of non-random sampling

Answer 10

• opportunistic
• stratified
• systematic

Question 11

describe opportunistic sampling

Answer 11

• using organisms that are conveniently available
• weakest form of sampling as those organisms may not be representative

Question 12

describe stratified sampling

Answer 12

dividing the population or habitat into sub-groups (strata) based on a particular characteristic. a random sample is then taken from each of these strata proportional to its size

Question 13

describe systematic sampling

Answer 13

• samples are taken at fixed intervals
• useful when studying how a gradient of an abiotic factor affects the species

Question 14

what are the two methods of systematic sampling

Answer 14

• line transect
• belt transect

Question 15

describe how to use a line transect

Answer 15

stretch a string or tape across a habitat and record the plants touching it at regular intervals

Question 16

describe how to use a belt transect

Answer 16

two parallel lines are marked and samples are taken of the area between the two lines or a quadrat can be placed at regular intervals along a tape

Question 17

describe how to use a frame quadrat

Answer 17

• place on ground and count the individuals inside it
• grids can be used to calculate %cover

Question 18

describe how to use a point quadrat. include how you would calculate percentage cover

Answer 18

• place on ground and anything that touches the point is recorded.
• move pin down quadrat and this can be used to identify percentage cover
• %cover = hits/number of pins x100

Question 19

what are the advantages and disadvantages of a frame quadrat

Answer 19

advantages:
- quick observation
- bigger area
disadvantages:
- more subjective

Question 20

what are the advantages and disadvantages of a point quadrat

Answer 20

advantages:
- more accurate
disadvantages:
- smaller area

Question 21

what is the ACFOR scale used for

Answer 21

to collect data on the abundance of each species

Question 22

what do each of the letters stand for in the ACFOR scale

Answer 22

• Abundant
• Common
• Frequent
• Occasional
• Rare
• (N)one

Question 23

what are the advantages and disadvantages of the ACFOR scale

Answer 23

advantages:
- quick
- can compare different types of organism
disadvantages:
- subjective
- bright, colourful organisms tend to be overestimated and visa versa

Question 24

what factors need to be considered when choosing quadrat size

Answer 24

• size of habitat
• size of organism
• how varied is habitat? - gradient?

Question 25

what are transects used to study

Answer 25

the distribution of organisms in relation to an abiotic factor

Question 26

describe the method used to carry out a transect

Answer 26

- establish an initial line using tape measure for distance and a compass bearing for direction - place quadrat and record at set distances (systematic) - repeat at different places in the same area

Question 27

how would your transect method vary if you wanted to find out how distance above low tide affects seaweed species found

Answer 27

measure height not distance - use levelling poles

Question 28

describe what a sweep net is and how to use one

Answer 28

- used for sampling insects and other small animals in grassland - sweep backwards and forwards through vegetation

Question 29

what is a pooter

Answer 29

small jar which small organisms are sucked into

Question 30

what is a Longworth Trap and how do you use one

Answer 30

- for live capture of small mammals - put straw and food into trap so organism can survive the night

Question 31

what is a pitfall trap

Answer 31

cup buried in ground that ground-crawling animals will fall into

Question 32

what is a Tullgren Funnel

Answer 32

used to get animals out of soil or leaf litter

Question 33

what is tree beating

Answer 33

shake branch of a tree or bush with a white sheet underneath to collect insects

Question 34

what is kick sampling

Answer 34

hold net underwater facing upstream and kick the ground a few times to uplift soil which is then carried into the net by the current

Question 35

what is a light trap

Answer 35

used to collect moths at night

Question 36

what is the formula for estimating population size

Answer 36

(number in first sample x number in second sample)/number of marked animals in second sample

Question 37

describe the full method used to calculate population size (mark-release-recapture)

Answer 37

- collect a random sample from the population and mark every individual - release them into the wild again and allow them to mix - collect a second random sample and count the number of marked individuals - complete calculation to find estimate

Question 38

what are the limitations of mark release recapture

Answer 38

- marked individuals are more likely to be caught again - "trap happy" - once released, animal may not reintegrate with wild population - small sample size - marking makes animals more likely to be predated