10.5 - Quantitative investigations of variation

Question 1

what is interspecific variation

Answer 1

when 1 species differs from another

Question 2

what is intraspecific variation

Answer 2

when members of the same species vary from one another

Question 3

what is sampling

Answer 3

• taking measurements of individuals, selected from the population of organisms which is being investigated
• these individuals should be representative of the whole

Question 4

what is sampling bias

Answer 4

• selection process may be biased
• investigator may be making representing choices deliberately/unwittingly
• e.g. only taking samples from dry areas to avoid mud

Question 5

what is chance

Answer 5

• even if sampling bias is avoided, the individuals may be (by chance) not representative
• e.g. the 50 buttercups chosen might just happen to be the 50 tallest in the population

Question 6

how do we prevent sampling bias

Answer 6

random sampling

Question 7

how is random sampling carried out

Answer 7

1) divide study area into a grid of numbered lines
2) using random numbers from a table or generated by a computer, obtain a series of coordinates
3) Take samples at the intersection of each pair of coordinates

Question 8

how can we completely remove chance from the sampling process

Answer 8

• we can’t, however….
• we can minimise it’s effects by:
  1) using a larger sample size
  2) analysis of the data collected

Question 9

how can using a larger sample size minimise the effects of chance from the sampling process

Answer 9

• the more individuals are selected = the smaller probability that chance will influence the result + less influence anomalies will have
• this therefore makes the data more reliable

Question 10

how can analysis of the data collected minimise the effects of chance from the sampling process

Answer 10

• the data can be analysed using statistical tests to determine the extent to which chance may have influenced the data
• these tests allow us to decide whether any variation observed is the result of chance or is more likely to have some other cause

Question 11

describe the features of a normal distribution curve

Answer 11

• bell-shape = shows continuous variation
• symmetrical around a central value (but can occasionally be slightly shifted to one side = called a skewed distribution)
• there are 3 terms associated with these:
  1) mean
  2) mode
  3) median
  –> all these 3 are found in the same place in a normal distribution curve, but not a skewed distribution

Question 12

what’s the mean

Answer 12

it’s the sum of the sampled values divided by the number of items

Question 13

what’s the mode

Answer 13

the single value of a sample that occurs most often

Question 14

what’s the median

Answer 14

• the central or middle value of a set of values
• requires arranging the values in ascending order

Question 15

what are the ways that normal distribution curves will vary/stay the same

Answer 15

same:
- have the same basic ‘bell-shape’

vary:
- its maximum height
- its maximum width

Question 16

describe what the mean is in relation to a normal distribution curve

Answer 16

• it’s the measurement at the maximum height of the curve
• it’s useful to compare averages between samples
• However, it doesn’t provide any info about the range of values within a sample

Question 17

describe what the standard deviation is in relation to a normal distribution curve

Answer 17

• it’s the measurement at the width of the curve
• gives an indication of the range of values either side of the mean
• A standard deviation is the distance from the mean to the point where the curve changes from being convex to concave
• 68% of all the measurements lie within +/- 1.0 standard deviation
• increasing this width to almost +/- 2.0 (actually +/-1.96) standard deviation takes in 95% of all measurements

Question 18

what is the formula for standard deviation

Answer 18

Question 19

how many significant figures do you normally round to

Answer 19

• 3
• but always use the same significant figures as given in the Q. Only do it to 3 if you are unsure

Question 21

What are sessile animals

Answer 21

Animals that dont move (non motile)

Question 22

How do you calculate the estimated population size from a mark-release-recapture

Answer 22

Question 23

What are the assumptions made for using the Mark-release-recapture technique

Answer 23

1) the portion of unmarked to marked individuals in the 2nd sample is the same as in the population as a whole
2) Marked individuals distributed themselves evenly among the rest of the population and had enough time to do so
3) Definite boundaries, no immigration/emigration
4) few deaths (if any) and births in the population
5) method of marking os non-toxic and doesn’t make the animal more conspicuous and more liable to predation
6) the mark, or label isn’t lost or rubbed off during the investigation