Controls and additive series
description
Transcript of Controls and additive series
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Controls and additive series
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Group exercise:
Read your stream control example, and decide on:
(1) What is wrong with the design?
(2) How you might fix it.
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Scenario 1
A B C A B C
Before After
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Scenario 2
A B C
D E F
+ pollutant
- pollutant
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What is the probability that the 3 “worst” streams are randomly assigned to the pollutant treatment?
3/6 * 2/5 * 1/4 = 2/40 or 5%
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Scenario 3
A B C A B CBefore After
D E F D E F
Before After
+ chemical in alkaline solution
control
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Scenario 4
A B C A B CBefore After
D E F D E F
Before After
+ pollutant
control
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0
5
10
15
20
25
30
35
40
45
control + pollutant
Det
rita
l los
s (m
g / w
eek)
with insectsno insects
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Scenario 5
?
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Insect abundance =
m1 * width +
m2 * dioxin +
m3 * width*dioxin +
Y-intercept
(and error)
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Summary of control types
Which scenarios lacked:
• Control for initial conditions?
• Unmanipulated, contemporaneous control?
• Control for side effect of manipulation?
• Control for covariates?
• Control for non-target response?
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BACI design
• Unmanipulated, contemporaneous control
• Initial conditions
Eg. Scenario 3
Before After
Before After
+ pollutant
control
Before After Control Impact
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BACI design
• Unmanipulated, contemporaneous control
• Initial conditions
Before After
+ pollutant
control
Before After Control Impact
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Study SiteRoadsHiking trail
WaterContour 100m ((10m)
Major Roads
Study Site
Legend
Camp
Sky
line
SICAMOUS
N
EW
S
Kamloops
Sicamous Sicamous
Kamloops
Example of BACI design:Ernest Leupin’s study
on forest fragments and birds
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Forest residue
Roads Openings Selection cut
N
C a m p M t . M a r a
H i k i n g
T r a i l
S k y l i n e
0 1 2 K i l o m e t e r s
Sicamous Creek Research Forest
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How can we analyze BACI designs?
Randomized block?
What is n?
What is k?
How many independent experimental units in total?
A treatment x date ANOVA?
Before After
Before After
+ pollutant
control
A B C A B C
D E F D E F
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How can we analyze BACI designs?
Randomized block?
A treatment x date ANOVA?
Before After
Before After
+ pollutant
control
A B C G H I
What is n?
What is k?
How many independent experimental units in total?D E F J K L
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How can we analyze BACI designs?
Two separate ANOVAs / t-tests?
Before After
Before After
+ pollutant
control
Different? Different?
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How can we analyze BACI designs?
Two separate ANOVAs / t-tests?
A B Cbefore after before after before after
Y variable
before after
Impact sites
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How can we analyze BACI designs?
• Need to have match the number of datapoints with the number of experimental units
• Need to take advantage of built-in control for stream identity
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How can we analyze BACI designs?
One solution:
Use difference between before and after as the data!
Before After
Before After
+ pollutant
control
A B C A B C
D E F D E F
Difference
Difference
A B C
D E F
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Example: Additive series design for container mosquito larvae
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1985
1996
Aedes albopictus invades N America from SE Asia in 1985, via used tire trade at Houston
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Breeds in containers habitats (old tires, treeholes), like native species, Aedes aegypti
Aedes albopictus
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Ranges overlap, potential for interspecific competition
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Experimental design (“Additive series”)
Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255-268.
Aedes aegypti
Aed
es a
lbop
ictu
s
Substitutive or
replacement series
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Experimental design (Additive series)
Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255-268.
Aedes aegypti
Aed
es a
lbop
ictu
s
Addition design
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Experimental design
Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255-268.
Aedes aegypti
Aed
es a
lbop
ictu
s Can asses Aedes aegypti performance in these treatments
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Hypotheses:
Aedes aegypti
Aed
es
alb
op
ictu
s
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse
Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse Albo has no effect
on Aeg, so effect of 1 Albo = 0 Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse
Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg
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Hypotheses:
Aedes aegypti
Aed
es
alb
op
ictu
s
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse
Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse Albo has no effect
on Aeg, so effect of 1 Albo = 0 Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse
Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg
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Results
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
su
rviv
ors
hip
ANOVA: treatment x food x tire(=block)
Followed by t-tests (posthoc)