Transcript File - Mrs Jones A

Starter
Hedgerows are important in farming as they act as sites of
refuge for beneficial insects, provide protection for the crop
from adverse weather conditions and act as wildlife corridors.
Farmers are advised to leave strips of land between
hedgerows and the crops in the fields to encourage
biodiversity.
Describe how you would investigate whether leaving strips
of land around fields encourages plant biodiversity.
Measuring Biodiversity
Species Richness is the number of species found within the habitat
Species Evenness is the abundance of individuals in each species
Species Richness
• Observe habitat
• Count different
species
• Sample using any
of the sampling
methods
• Record results
Plant Species Evenness
• Random sampling
using quadrats
• Count the number of
plants of each species
per unit area (larger
plants) or measure %
cover (smaller plants
 To study a habitat, you have to count the number of individuals of a
species in a given space.
 This is known as abundance.
 Very difficult to identify and count every organism – this would be time
consuming and may damage the habitat.
 Small sections of the habitat are studied in detail.
 As long as the sample is representative of the habitat, any conclusions
drawn from findings will be valid.
B2a – Collection and Sample Size
Learning Objectives:
-To estimate population sizes
- To use keys to identify animals and plants
Starter:
1. Look at this picture and guess the percentage of the field that
is covered by:
a) Bluebells
b) Poppies
2. Guess the number of ants in
this field…
How easy was it to guess?
How accurate do you think you were?
There are more accurate ways to make
estimations…
…e.g. quadrats
Three factors need to be considered when using quadrats;
 The size of the quadrat to be used – larger species require larger
quadrats. Where a species occurs in small groups rather than being evenly
distributed, a large number of small quadrats will give more representative
results.
 The number of sample quadrats to record within the study area – the
larger the number of sample quadrats, the more reliable the results. The
greater the number of different species present in the area being studied,
the greater the number of quadrats required to produce valid results.
 The position of each quadrat within the study area – to produce
statistically significant results, random sampling must be used.
Random sampling avoids bias in collecting data.
Investigating the effects of grazing animals on the species of plants
growing in a field
 Choose 2 fields close together – minimises soil, climatic and
other abiotic differences.
 Take random samples at many sites in each field.
 Even with the best of intentions, it is difficult to avoid
introducing an element of personal bias.
 E.g. are you more likely to stand in a dry area than a wet one?
 Will you deliberately avoid areas with nettles and sheep
droppings?
A better method of random sampling is to;
 Lay out two long tape measures at right angles along 2 sides of
the study area.
 Obtain a series of coordinates by using random numbers taken
from a table or generated by a computer.
 Place a quadrat at the point of intersection and record the
species within it.
 Occasionally, measuring abundance in a systematic manner as opposed to
a random manner can be more informative.
 A line transect is made up of a string or tape stretched across the
ground in a straight line.
 Any organism over which the line passes is recorded.
 A belt transect is usually a strip, about a metre wide. The second line is
placed parallel to the first.
 Species occurring within the belt between the lines are recorded.
 Random sampling with quadrats and counting along transects are used to
obtain measures of abundance.
 Abundance = number of individuals of a species within a given space.
 Can be measured in 2 ways;
 Frequency - the likelihood of a particular species occurring in a
quadrat.
 Percentage cover – an estimate of the area within a quadrat that
a particular plant species covers.
 To determine species diversity in a habitat using random sampling
 To calculate species diversity index
Once the results of your investigation have been
recorded a statistical test is required to determine
the diversity of the habitat.
A diversity index allows us to estimate the variety of
living organisms in a particular area. It takes into
account species richness and species evenness.
Simpson’s Diversity Index
•
Stream 1 appears to be more diverse (it has more species than stream 2, it
is more species rich). However it has one species of 85 individuals and 15
species of one individual. Stream 2 has more individuals in each group so
this stream appears to be the most diverse (it is demonstrating species
evenness).
No of
species
Lugworms
Stonefly
larvae
Mayfly
larvae
Others
Stream 1
(100 animals)
16
85
0
0
15
Stream 2
(100 animals)
10
15
28
32
25
• To stop us making the wrong conclusion we can use the Simpson’s
Diversity Index!
• The formula is: D = 1 – [∑(n/N)2]
Simpson’s Index of Diversity
Diversity can be quantified by statistical methods, one of
which is Simpson’s Index of Diversity:
N(N – 1)
D =
∑ n(n – 1)

N = the total number of organisms of all species

n = total number of organisms of a particular species

D = diversity index: the probability that two randomly
selected individuals will belong to the same species/group.
The lowest possible value of D is 1. The larger the value
of D, the greater the diversity.
Two fields were compared and investigated to determine their biodiversity.
Data is from 200 point quadrats
Species
Field A
Field B
Foxtail Grass
80
96
Clover
9
2
Black Medick
22
12
Daisy
13
0
Dandelion
3
2
Self Heal
14
12
Moss
36
26
Field A
n
n/N
Field B
(n/N)2
n
Foxtail Grass
80
96
Clover
9
2
Black Medick
22
12
Daisy
13
0
Dandelion
3
2
Self Heal
14
12
Moss
36
26
N
177
150
∑ (n/N)2
1 –[ ∑ (n/N)2]
n/N
(n/N)2
Field A
n
n/N
Foxtail Grass
80
Clover
Field B
(n/N)2
n
n/N
0.4519
96
0.6400
9
0.0508
2
0.0133
Black Medick
22
0.1242
12
0.0800
Daisy
13
0.0734
0
0.0000
Dandelion
3
0.0169
2
0.0133
Self Heal
14
0.0790
12
0.0800
Moss
36
0.2033
26
0.1733
N
177
∑ (n/N)2
1 –[ ∑ (n/N)2]
150
(n/N)2
Field A
n
n/N
Foxtail Grass
80
Clover
Field B
(n/N)2
n
n/N
0.4519
96
0.6400
9
0.0508
2
0.0133
Black Medick
22
0.1242
12
0.0800
Daisy
13
0.0734
0
0.0000
Dandelion
3
0.0169
2
0.0133
Self Heal
14
0.0790
12
0.0800
Moss
36
0.2033
26
0.1733
N
177
∑ (n/N)2
1 –[ ∑ (n/N)2]
150
(n/N)2
Field A
Field B
n
n/N
(n/N)2
n
n/N
(n/N)2
Foxtail Grass
80
0.4519
0.2042
96
0.6400
0.4096
Clover
9
0.0508
0.0025
2
0.0133
0.0001
Black Medick
22
0.1242
0.0154
12
0.0800
0.0064
Daisy
13
0.0734
0.0053
0
0.0000
0.0000
Dandelion
3
0.0169
0.0002
2
0.0133
0.0001
Self Heal
14
0.0790
0.0062
12
0.0800
0.0064
Moss
36
0.2033
0.0410
26
0.1733
0.0300
N
177
150
∑ (n/N)2
0.2748
0.4520
1 –[ ∑ (n/N)2]
0.7252
0.5480
Analysis and Conclusion
What is the Simpson’s Diversity Index for Field A and B
Read information on pg199
What do these figures Indicate?
• The Simpson’s Diversity Index for Field A is 0.7252 and for Field B
is 0.5480.
• A high value for Simpson’s Diversity Index indicates a diverse
habitat. The closer to 1 the value, the higher the biodiversity and the
more stable the habitat. Small changes in one species may not
have a large affect on the other species in the habitat.
• A low value for Simpson’s Diversity Index indicates a habitat
dominated by fewer species. Therefore small changes to the
environment may affect one species but because of its dominance in
the community the changes to this species may affect the entire
habitat.
• Field A is more biodiverse than Field B.