Sampling

Question 1

3 different ways we make sample accurately represent population.

Answer 1

• Random sampling (in areas of even distribution) to eliminate bias.
• Line transects to examine change over distance.
• Large no of samples (ie. 30)

Question 2

What 2 different types of organisms can we estimate the population size of using sampling?

Answer 2

• Slow moving or non-motile organisms.
• Motile organisms

Question 3

If we have slow moving or non-motile organisms, how do we sample them to estimate the population size?

Answer 3

• Use quadrats.
• Even distribution–> randomly-placed quadrats.
• Uneven distibution –> quadrats along a line belt transect.

Question 4

What is meant by even vs uneven distribution? Give example of each.

Answer 4

• Even: populations which remain same in 1 given area ie. a field.
• Uneven: populations which change over distance ie. from top of beach to shore-line.

Question 5

What 2 different types of line transects are there?

Answer 5

1.) Belt transect: quadrat is placed at every poisition along tape measure (ie. keep flipping the quadrat over, leaving no gaps.)
2.) Interrupted belt transect: quadrat placed at uniform intervals along tape measure ie. every 5m.

() - extra info for clarification

Question 6

2 different types of quadrats?

Answer 6

• Open.
• Divided into 100 squares.

Question 7

What is the method for random sampling?

Answer 7

1.) Lie 2 tape measures at right angle to create gridded area.
2.) Use random no. generator to generate two co-ordinates (one horizontal, other vertical.)
3.) Place quadrat and collect data: either percentage cover, density, frequency.
4.) Repeat at least 30 times, calculate mean.

() - extra info for clarification.

Question 8

Give 2 examples of uneven distribution of populations.

Answer 8

• Sandy/ rocky shores.
• Across path/ river.

Question 9

What is the method for using a line transect to estimate the population size?

Use example of from shore line to sand

Answer 9

1.) Place tape measure at right angle to shore line.
2.) Place the quadrat every 5m OR every position along the transect.
3.) Collect data (density/ percentage cover/ frequency.)
4.) Repeat by placing another 30 transects along beach at right angles to shore line.

Image of this on Miss Estreuch video

Question 10

Sampling method to estimate population size in motile organisms?

Answer 10

• Mark-release- recapture method.

Question 11

What are the 3 different methods to estimate the abundance of a species in a field?

Answer 11

1.) Local frequency: % of squares in quadrat with species present.
2.) Density: the number of one or different species in a given area.
3.) Percentage cover: proportion of quadrat occupied by species (if species arranged right next to each other, what proportion of quadrat would it fill- this gives percentage cover.)

() - extra info for clarification.

Question 12

Advantages/ disadvantages of the “local frequency” method to estimate abundance of species in field?

Answer 12

• A: quick method to sample large area.
• A: Useful if too many individual organisms to count.
• D: poor accuracy, doesn’t consider overlapping/ size of species.

() - extra info for clarification.

Question 13

Advantages/ disadvantages of the “density” method to estimate abundance of species in field?

Answer 13

• A: more accurate if not too many to count.
• A: can estimate species richness.
• D: more time-consuming.

Question 14

Advantages/ disadvantages of the “percentage cover” method to estimate abundance of species in field?

Answer 14

• A: quicker than “density.”
• D: doesn’t consider overlapping/ size of plant.

Question 15

Method for “mark-release, recapture?”

Answer 15

1.) Initial sample captured and individuals are marked/ released into wild. Number captured = recorded.
2.) Marked are released and left to randomly disperse throughout habitat.
3.) Second sample captured.
4.) Total no. of individuals captured = recorded/ no. recaptured w/marking is recorded.
5.) Repeat steps 1-4 multiple times.

Question 16

What properties should the substance used to mark the organism have?

Answer 16

• Weather-resistant.
• Non-toxic
• Must not increase chances of predation ie. not bright colour.
• Must not reduce chances of reproduction.

Question 17

On what principle is the size of population estimated using mark-release recapture method?

Answer 17

• Proportion marked in 2nd sample = proportion of marked individuals in whole population.

Question 18

Why would we repeat the steps of the mark-release recapture method multiple times?

Answer 18

• Makes results more reliable.

Question 19

Equation for estimating population size of motile organisms using mark-release recapture.

Need to learn equation, NOT given!

Answer 19

Estimated total population = number of organisms intially caught x number of organisms in 2nd sample/ number of marked organisms recaptured.

Question 20

How must you CAPTURE and MARK the organisms in the mark-release recapture method?

Answer 20

• Must cause no permanent harm.

Question 21

Why might the estimated population size generated from mark-release recapture not be accurate?

Answer 21

Due to assumptions:
1.) The population size is constant (no birth/ death/ migration.)
2.) Animals all re-distribute evenly (may all huddle near food.)

Question 22

Past Paper Q

Equation for mark-release recapture.

Answer 22

Estimated total population = number of organisms in first sample x number of organisms in 2nd sample DIVIDED BY number of marked organisms recaptured.

Question 23

MS answer 2024 paper 2.

Why should substance used to mark organisms in mark, release, recapture be:
1.) non-toxic
2.) non-fluorescent.

Answer 23

1.) Non-toxic: so doesn’t affect organism’s survival.
2.) Non-fluorescent: ensure not visible to predators.