Ut the study. ance, when determining tree one, the quadrat may only be 0.25 m² because much smaller organisms are being studied. 10m because of the size of the study species, in a rocky Quadrat surveys are useful in rocky intertidal areas because the majority of organisms located there are slow-moving, attached to the substrate or plants. Scientists use a method of random sampling to determine where to place the quadrat when conducting a survey. This prevents any bias affecting the data. The counts from each quadrat are then averaged to reach an approximate number for the entire area. Scientists were conducting a quadrat survey on a rocky shore in Vancouver, BC, Canada. They were specifically investigating the abundance of leather stars (Dermasterias imbricate) and the Pacific blue mussel (Mytilus trossulus) along the shore. Square quadrats of 1 m² were used to measure the abundance in ten randomly selected locations (see Table 6.3). sample area number of leather 3 stars in 1 m² number of mussels 20 in 1 m² 2 15 49 3 0 9 47 Table 6.3. Results of 1 m² sample area calculations. 5 12 6 17 7 12 100 48 8 - 10 9 2 16 10 32

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Using the example from table 6.4 , calculate the mean numbers and standard deviation of the pousing the data in table 6.3

Is of the study.
may be 10 m³ because of the size of the study species; in a rocky
y. For instance, when determining Tree
al zone, the quadrat may only be 0.25 m² because much smaller organisms are being studied.
Quadrat surveys are useful in rocky intertidal areas because the majority of organisms located there
are slow-moving, attached to the substrate or plants.
Scientists use a method of random sampling to determine where to place the quadrat when
conducting a survey. This prevents any bias affecting the data. The counts from each quadrat are then
averaged to reach an approximate number for the entire area.
Scientists were conducting a quadrat survey on a rocky shore in Vancouver, BC, Canada. They were
specifically investigating the abundance of leather stars (Dermasterias imbricate) and the Pacific
blue mussel (Mytilus trossulus) along the shore. Square quadrats of 1 m² were used to measure the
abundance in ten randomly selected locations (see Table 6.3).
sample area
number of leather 3
stars in 1 m²
number of mussels 20
in 1 m-
2
15
49
3
0
9
8
47
Table 6.3. Results of 1 m² sample area calculations.
5
4
12
6
17
100
7
12
48
8
1
10
9
2
16
10
9
32
Transcribed Image Text:Is of the study. may be 10 m³ because of the size of the study species; in a rocky y. For instance, when determining Tree al zone, the quadrat may only be 0.25 m² because much smaller organisms are being studied. Quadrat surveys are useful in rocky intertidal areas because the majority of organisms located there are slow-moving, attached to the substrate or plants. Scientists use a method of random sampling to determine where to place the quadrat when conducting a survey. This prevents any bias affecting the data. The counts from each quadrat are then averaged to reach an approximate number for the entire area. Scientists were conducting a quadrat survey on a rocky shore in Vancouver, BC, Canada. They were specifically investigating the abundance of leather stars (Dermasterias imbricate) and the Pacific blue mussel (Mytilus trossulus) along the shore. Square quadrats of 1 m² were used to measure the abundance in ten randomly selected locations (see Table 6.3). sample area number of leather 3 stars in 1 m² number of mussels 20 in 1 m- 2 15 49 3 0 9 8 47 Table 6.3. Results of 1 m² sample area calculations. 5 4 12 6 17 100 7 12 48 8 1 10 9 2 16 10 9 32
0
•
Often scientists include standard deviation in their results when they analyse their data. Standard
deviations tell you how spread out the numbers in a data set are. The smaller the standard deviation,
within a community. The equation for standard deviation is:
the closer the numbers are to the mean. This can tell you, for example, how variable a population is
These symbols all relate to the different steps you need to complete to find the standard deviation.
given in Table 6.3 is calculated as shown below.
This equation can be broken down into stages. The standard deviation (S) for the leather star data
Calculate the mean value (F) for the leather star population:
sample area
number of
leather stars
in 1 m²
(x-x)²
(x-x). So for quadrat 1: (3 - 7.1)² = 16.8.
Then for each quadrat, subtract the mean (x) from its number (x) and square the result, giving you:
Table 6.4 shows the results of this step for all 10 quadrats.
I
3
10
2
15
X = (3+15+0+8+4+17+12+1+2+9)
10
3
0
S= Σ(x-x)²
V #-1
4
8
16.8 62.4 50.4 0.8
5
4
9.6
6
17
7
12
98.0 24.0
8
= 7,1
1
Chapter 6: The ocean floor and the co
9
2
10
9
mean
Table 6.4. Working out the mean values for the leather stars.
The next step is to calculate E(x-x) by adding all of the (x-) values. So, E(x - x)² = 328.81
11
Then, divide your value for E(x-x)2 by (n-1), where is the number of values you have
(10, in this case). This should provide you with a value of 36.53.
Finally, take the square root of your calculated value.
• Using this equation, your standard deviation should be 6.04.
7.1
37.2 26.0 3.61 32.9
I a Calculate the mean numbers per m² for the mussels, using the data in Table 6.3.
b Calculate the standard deviation for the population of mussels.
2 Based on your knowledge of rocky intertidal zone communities, predict which quadrats were
placed in the lower intertidal zone and which were placed in the upper intertidal zone.
37157
2017-1
1
71
Transcribed Image Text:0 • Often scientists include standard deviation in their results when they analyse their data. Standard deviations tell you how spread out the numbers in a data set are. The smaller the standard deviation, within a community. The equation for standard deviation is: the closer the numbers are to the mean. This can tell you, for example, how variable a population is These symbols all relate to the different steps you need to complete to find the standard deviation. given in Table 6.3 is calculated as shown below. This equation can be broken down into stages. The standard deviation (S) for the leather star data Calculate the mean value (F) for the leather star population: sample area number of leather stars in 1 m² (x-x)² (x-x). So for quadrat 1: (3 - 7.1)² = 16.8. Then for each quadrat, subtract the mean (x) from its number (x) and square the result, giving you: Table 6.4 shows the results of this step for all 10 quadrats. I 3 10 2 15 X = (3+15+0+8+4+17+12+1+2+9) 10 3 0 S= Σ(x-x)² V #-1 4 8 16.8 62.4 50.4 0.8 5 4 9.6 6 17 7 12 98.0 24.0 8 = 7,1 1 Chapter 6: The ocean floor and the co 9 2 10 9 mean Table 6.4. Working out the mean values for the leather stars. The next step is to calculate E(x-x) by adding all of the (x-) values. So, E(x - x)² = 328.81 11 Then, divide your value for E(x-x)2 by (n-1), where is the number of values you have (10, in this case). This should provide you with a value of 36.53. Finally, take the square root of your calculated value. • Using this equation, your standard deviation should be 6.04. 7.1 37.2 26.0 3.61 32.9 I a Calculate the mean numbers per m² for the mussels, using the data in Table 6.3. b Calculate the standard deviation for the population of mussels. 2 Based on your knowledge of rocky intertidal zone communities, predict which quadrats were placed in the lower intertidal zone and which were placed in the upper intertidal zone. 37157 2017-1 1 71
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