Sampling Flashcards

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1
Q

Why might scientists use random sampling?

A

reduce/avoid bias
allows the use of statistical tests

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2
Q

Describe how the population of non-motile organisms can be estimated

A

using quadrats

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3
Q

How can the population size of motile organisms be estimated?

A

mark-release-recapture

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4
Q

Outline the steps involved in mark-release-recapture

A
  • capture and mark sample
  • release back into habitat and leave time for redistribution
  • recapture a sample
  • count the number of marked individuals
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5
Q

Give the equation used in the mark-release-recapture method

A

estimated pop. size = (initial capture * no. in 2nd sample) / no. of 2nd sample that were marked

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6
Q

What assumptions are made in the mark-release-recapture method?

A
  • enough time for even distribution
  • no immigration/emigration
  • birth rate = death rate
  • no marks rub off/are lost
  • the mark is not toxic/does not limit survival
  • proportion in 2nd sample is equal to proportion in whole population
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7
Q

Why is sampling used?

A
  • time efficient
  • can be more accurate if done correctly
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8
Q

How can sampling be made more accurate?

A
  • random used in uniform distribution
  • line transects to examine change over distance
  • large number of samples (30+)
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9
Q

What are the 2 types of quadrats?

A

open or gridded

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10
Q

What is the first step in random sampling?

A
  • lie 2 tape measures at a right angle to create a gridded areas
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11
Q

Describe how you would use random sampling to investigate population size

A

KEY POINTS
1) 2 tape measures, right angle, gridded area
2) Random number generator, co-ordinates
3) place quadrat, collect data (local freq, pop. density or % cover)
4) repeat (30+ times), calculate mean

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12
Q

What are the 2 types of transect?

A

belt or interrupted belt

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13
Q

Describe how you would use systematic sampling to investigate change over distance

A

KEY POINTS
- place tape measure, transect line
- place quadrat every X metres or every position
- collect data (pop. density, % cover, frequency)
- repeat (30+)

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14
Q

What are the advantages and disadvantages of local frequency?

A

+VES: quick, useful if too many to count
-VES: poor accuracy as doesn’t consider size or overlap

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15
Q

What are the advantages and disadvantages of population density?

A

+VES: more accurate if plant is distinguishable and not too many, can be used to estimate species richness
-VES: more time consuming

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16
Q

What are the advantages and disadvantages of percentage cover?

A

+VES: quicker than density, useful if indistinguishable or too many
-VES: subjective (limits accuracy), doesn’t consider size or overlap

17
Q

Why might mark-release recapture be unreliable in larger sample areas?

A
  • unlikely species will distribute evenly
  • less likely to recapture fish