Controls and additive series. Group exercise: Read your stream control example, and decide on: (1) What is wrong with the design? (2) How you might fix.

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Presentation transcript:

Controls and additive series

Group exercise: Read your stream control example, and decide on: (1) What is wrong with the design? (2) How you might fix it.

Scenario 1 A B C A B C Before After

Scenario 2 A BC D EF + pollutant - pollutant

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%

Scenario 3 A BC A BC BeforeAfter D EF D EF Before After + chemical in alkaline solution control

Scenario 4 A BC A BC BeforeAfter D EF D EF Before After + pollutant control

Scenario 5 ?

Insect abundance = m1 * width + m2 * dioxin + m3 * width*dioxin + Y-intercept (and error)

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?

BACI design Unmanipulated, contemporaneous control Initial conditions Eg. Scenario 3 BeforeAfter Before After + pollutant control Before After Control Impact

BACI design Unmanipulated, contemporaneous control Initial conditions BeforeAfter + pollutant control Before After Control Impact

Study SiteRoads Hiking trail Water Contour 100m ((10m) Major Roads Study Site Legend Kamloops Sicamous Kamloops Example of BACI design: Ernest Leupin’s study on forest fragments and birds

Sicamous Creek Research Forest

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? BeforeAfter Before After + pollutant control ABCABC DEFDEF

How can we analyze BACI designs? Randomized block? A treatment x date ANOVA? BeforeAfter Before After + pollutant control ABCGHI What is n? What is k? How many independent experimental units in total? DEFJKL

How can we analyze BACI designs? Two separate ANOVAs / t-tests? BeforeAfter Before After + pollutant control Different?

How can we analyze BACI designs? Two separate ANOVAs / t-tests? ABC before after Y variable before after Impact sites

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

How can we analyze BACI designs? One solution: Use difference between before and after as the data! BeforeAfter Before After + pollutant control ABCABC DEFDEF Difference ABC DEF

Example: Additive series design for container mosquito larvae

Aedes albopictus invades N America from SE Asia in 1985, via used tire trade at Houston

Breeds in containers habitats (old tires, treeholes), like native species, Aedes aegypti Aedes albopictus

Ranges overlap, potential for interspecific competition

Experimental design (“Additive series”) Juliano, S Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: Aedes aegypti Aedes albopictus Substitutive or replacement series

Experimental design (Additive series) Juliano, S Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: Aedes aegypti Aedes albopictus Addition design

Experimental design Juliano, S Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: Aedes aegypti Aedes albopictus Can asses Aedes aegypti performance in these treatments

Hypotheses: Aedes aegypti Aedes albopictus aeg albo Aedes aegypti response Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg aeg albo Aedes aegypti response Albo has no effect on Aeg, so effect of 1 Albo = 0 Aeg aeg albo Aedes aegypti response Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg

Hypotheses: Aedes aegypti Aedes albopictus aeg albo Aedes aegypti response Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg aeg albo Aedes aegypti response Albo has no effect on Aeg, so effect of 1 Albo = 0 Aeg aeg albo Aedes aegypti response Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg

Results aeg albo Aedes aegypti survivorship ANOVA: treatment x food x tire(=block) Followed by t-tests (posthoc)