Assessing Species Diversity (Chapter 18)

Question 1

What is the first task when assessing species diversity?

Answer 1

To identify and catalogue the types of organisms and build a species list

Question 2

What are used to identify organisms found?

Answer 2

• Identification keys
• Most common = dichotomous key
• If you can’t identify the organism, take photos and label the species as species A etc

Question 3

What is a pooter and how does it work?

Answer 3

• Apparatus used to collect small animals e.g. insects
  1) breathe air into the mouth of the pooter, sucking up small animals into a plastic container
  2) remove and study the animals and then returns them to their habitat

Question 4

What would be the ideal way to find out which species are present in an ecosystem and the size of populations but why is this not normally done?

Answer 4

• Ideal method = to find, identify and count every single organism in an ecosystem
• BUT can only do this if the area is very small or the species are very large
• Instead, samples are taken from the area and used to make an estimate of the total numbers in the area

Question 5

What are the two things sampling can be?

Answer 5

1) random

2) systematic

Question 6

When is it best to use random sampling?

Answer 6

If an area looks reasonably uniform, or if there is no clear pattern to the way species are distributed

Question 7

What do you use for random sampling?

Answer 7

A quadrat

Question 8

What is a quadrat?

Answer 8

A square frame that marks off an area of ground or water, where you can identify the different spices present and/or take a measurement of their abundance

Question 9

What 2 things do you need to decide on about the quadrat before using it

Answer 9

1) need to decide on a suitable size for the quadrat (e.g. 1m2)
2) how many samples you will take

Question 10

Why must samples be taken randomly?

Answer 10

To avoid any bias

Question 11

How could bias be present?

Answer 11

If you choose the place with the fewest species to take all the samples because it is the easiest, this would not be representative of the whole area being surveyed

Question 12

How do you ensure that your sample is random?

Answer 12

Mark out an area with measuring tapes and use a random number generator e.g. app on phone to generate random numbers which give you the coordinates of the sampling points in relation to the two tapes used to mark out the area

Question 13

What is species frequency?

Answer 13

A measure of the chance of a particular species being found within any one quadrat

Question 14

How do you work out species frequency?

Answer 14

1) record whether species was present in each quadrat placed

2) e.g. if found daises in 22 quadrats out of 50: species frequency = 22/50 x 100 =44%

Question 15

What is species density?

Answer 15

A measure of how many individuals there are per unit area e.g. per m2

Question 16

How do you work out species density?

Answer 16

The number of individuals counted is divided by the total area of the quadrats

Question 17

When would you need to estimate percentage cover of a species within a quadrat?

Answer 17

When it is not possible to count individual plants and animals because of the way they grow e.g. many plants and animals grow over surfaces forming a covering

Question 18

How would you estimate percentage cover of grass plants on a lawn?

Answer 18

1) use 1mx1m quadrate with wires running across 10cm intervals in each direction, dividing the quadrat into 100 smaller squares
2) decide approximately what % of the area inside the quadrat is occupied by each species - percentages may not add up to 100% e.g. if bare ground or overlapping plants
3) OR use an abundance scale e.g. Braun-Blanquet scale for plants to estimate percentage cover of each species (assigns value 0-5 for ranges of % cover e.g. >75% = 5)

Question 19

When can you not use quadrats?

Answer 19

For finding or counting mobile animals

Question 20

What are methods for counting specific types of mobile animals?

Answer 20

1) small mammals - use traps filled with hay and suitable food as bait
2) insects and invertebrates - sweep netting
3) aquatic organisms - pond nets
4) single birds - can be counted quite easily but more difficult in dense forest
5) flocks of birds - count a group of 10 birds and estimate how many such groups there are

Question 21

What is a good method of estimating the population size of mobile organisms?

Answer 21

The mark-release-recapture method

Question 22

Describe how you would use the mark-release-recapture technique to estimate the number of mobile animals

Answer 22

1) catch as many individuals of a species as possible
2) mark each individual, in a way that will not affect its future chance of survival
3) count the marked individuals, return them to their habitat and leave them to mix randomly with the rest of the population
4) when enough time has elapsed for the mixing to take place, capture another large sample
5) count the number of marked and unmarked individuals
6) use the proportion of marked to unarmed individuals to calculate an estimate of the total number in the population
e. g. if 1/10 of the second sample are marked, estimate that the population is 10 x the number caught and marked in the first sample

Question 23

How do you estimate the number of individuals of a species in a population?

Answer 23

(no caught in first sample x no caught in second sample) / (no in second sample that had been marked)

Question 24

When is random sampling not suitable for surveying a place?

Answer 24

If you want to investigate how species are distributed in an area where the physical conditions change e.g. altitude, soil pH, light intensity, soil moisture content

Question 25

How would you use a line transect to investigate the change in species at the edge of a field?

Answer 25

1) randomly select a starting point in the field and lay out a measuring tape in a straight line to the edge of the field
2) sample the organisms that are present along the line (line transect) by recording the identity of the organisms that touch the transect at set distances e.g. every 2m
3) this line transect will give you qualitative data that can be shown as a drawing

Question 26

How would you use an (interrupted) belt transect to investigate the change in species at the edge of a field?

Answer 26

1) use a (interrupted) belt transect by placing a quadrat at regular intervals along the line and recording the abidance of each species within the quadrat
2) date from a belt transect can be plotted as a set of bar charts or as a kite diagram (x = species, y = distance along line, width of kite = abundance (0-5)

Question 27

What can the Simpsons Index of Diversity be used for?

Answer 27

To calculate a value for the species diversity in an area

Question 28

What is the formula for the Simpsons Index of Diversity and what do each of the letters stand for?

Answer 28

• D = 1 - (sum of(n/N)2)
• n = total number of organisms of a particular species
• N= total number of organisms of all species

Question 29

What do values of D range from?

Answer 29

0-1

Question 30

What do the values of D mean?

Answer 30

• Near 0 = very low species diversity

- Near 1 = very high species diversity

Question 31

What can the Simpsons Index of Diversity be used to compare?

Answer 31

Species diversity in different areas

Question 32

What should be true when using D to compare species diversity?

Answer 32

Communities in each area and the organisms chosen should be similar (e.g. 10 of the same organisms for each area)

Question 33

What is the advantage of using D to compare species diversity?

Answer 33

Do not need to identify the organisms present to the level of species - just need to distinguish them

Question 34

When might you use correlation?

Answer 34

If you want to know if there is an association between two species which always seem to occur together OR if there is any relationship between distribution and abundance of a species and an abiotic factor e.g. soil moisture content

Question 35

How can you decide if there is an association between two species?

Answer 35

Plot a scatter graph and 1) make a judgement by eye

2) calculate a correlation coefficient ( r ) to assess the strength of a correlation suspect to exist

Question 36

What is the strongest correlation and what are positive/negative correlations?

Answer 36

• Strongest = linear (r=1)
• Positive = as variable A increases, variable B increases
• Negative = as variable A increases, variable B decreases

Question 37

What does it mean if r=0?

Answer 37

There is no correlation at all

Question 38

When, and only when, can the Pearson’s correlation coefficient be used?

Answer 38

1) when there is a linear correlation
2) with quantitive data (height) or counts (no of species in quadrat)
3) when data is distributed normally

Question 39

What is the strength of the correlation shown by on a scatter graph?

Answer 39

How close the points are to the straight line

Question 40

What does the Pearson’s r need?

Answer 40

Data for two continuous variables and data within each variable to show a normal distribution

Question 41

What is the range of rp?

Answer 41

-1 to +1

Question 42

What does the value of rp signify?

Answer 42

• -1 = negative correlation
• 0 = no correlation
• +1 = positive correlation

Question 43

What must you do before working out rp?

Answer 43

1) check whether relationship between the two continuous variables appears to be linear by drawing a scatter graph (doesn’t matter on which axis variables are plotted)
2) check data is normally distributed

Question 44

What is the equation for rp and what do the letters stand for?

Answer 44

• rp = (sum of(xy) - n(mean of x)(mean of y))/(nSxSy)
• x = number of species A in a quadrat
• y = number of species B in a quadrat
• n = number of readings (number of quadrats)
• mean of x/y = mean number of species A/B
• Sx/y = SD for numbers of species A/B

Question 45

When do you use the Spearman’s rank correlation?

Answer 45

1) if data is not quantitive e.g. % cover or have used abundance scale
2) if not sure whether the quantitive data is normally distributed
3) if data is correlated, but not linearly

Question 46

How would you decide whether to use Spearman’s rank to figure out the correlation between % over of two species?

Answer 46

1) make a null hypothesis that there is no correlation between the percentage cover of the two species
2) draw a scatter graph to see if it looks as if there is a correlation between the abundance of the two species

Question 47

What do you do before using rs?

Answer 47

1) rank each set of data - e.g. if you have 10 quadrats, and quadrat 4 for species A had the highest percentage cover, quadrate 4 is ranked 10 etc
2) once both sets of data have been ranked, calculate the differences in rank (D) by subtracting the rank of species B from the rank of species A for each quadrat
3) square each value of D and ad them together to find sum of D2

Question 48

What is the equation for Spearman’s rank and what do the letters stand for?

Answer 48

• rs = 1 - ((6xsum of D2)/(n3-n))
• sum of D2 = the sum of the differences between the ranks of the two samples squared
• n = number of samples

Question 49

What happens if the rs is very close to +1 (same as rp)?

Answer 49

1) it is very likely that there is a positive correlation between two species and that the strength of the association is very high
2) ∴ reject the null hypothesis and accept alternative hypothesis that there is a correlation between the abundance of species A and species B

Question 50

How do you compare two critical values of rs at the 0.05 probability level?

Answer 50

1) if n=10, degrees of freedom = 9, critical value at 0.05 = x
2) if our value is more than x, accept that there is a significant correlation between the % cover (number of species) of species A and species B
3) value indicates a probability of 0.05 or less, ∴ null hypothesis is not supported