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Controls and additive series

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. C. C. A. A. B. B. Scenario 1. Before. After. Scenario 2. B. C. A. + pollutant. E. F. D. - pollutant.

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Controls and additive series

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  1. Controls and additive series

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

  3. C C A A B B Scenario 1 Before After

  4. Scenario 2 B C A + pollutant E F D - pollutant

  5. 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%

  6. Scenario 3 Before After B C B C A A + chemical in alkaline solution Before After E F E F D D control

  7. Before After B C B C A A Before After E F E F D D Scenario 4 + pollutant control

  8. Scenario 5 ?

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

  10. 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?

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

  12. BACI design Before After Control Impact • Unmanipulated, contemporaneous control • Initial conditions Before After control + pollutant

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

  14. Sicamous Creek Research Forest

  15. A treatment x date ANOVA? Before After A B C A B C + pollutant Before After control D E F D E F How can we analyze BACI designs? Randomized block? What is n? What is k? How many independent experimental units in total?

  16. Before After + pollutant Before After control How can we analyze BACI designs? Randomized block? A treatment x date ANOVA? What is n? What is k? How many independent experimental units in total? A B C G H I D E F J K L

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

  18. How can we analyze BACI designs? Two separate ANOVAs / t-tests? Impact sites Y variable before after before after before after before after A B C

  19. 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

  20. How can we analyze BACI designs? One solution: Use difference between before and after as the data! Before After Difference A B C A B C A B C + pollutant Before After Difference control D E F D E F D E F

  21. Example: Additive series design for container mosquito larvae

  22. Aedes albopictus invades N America from SE Asia in 1985, via used tire trade at Houston 1985 1996

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

  24. Ranges overlap, potential for interspecific competition

  25. Experimental design (“Additive series”) Aedes albopictus Substitutive or replacement series Aedes aegypti Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255-268.

  26. Experimental design (Additive series) Aedes albopictus Addition design Aedes aegypti Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255-268.

  27. Experimental design Can asses Aedes aegypti performance in these treatments Aedes albopictus Aedes aegypti Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255-268.

  28. Hypotheses: Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg Aedes aegypti response aeg 20 20 40 60 albo 0 40 20 0 Aedes albopictus Albo has no effect on Aeg, so effect of 1 Albo = 0 Aeg Aedes aegypti response Aedes aegypti aeg 20 20 40 60 albo 0 40 20 0 Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg Aedes aegypti response aeg 20 20 40 60 albo 0 40 20 0

  29. Hypotheses: Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg Aedes aegypti response aeg 20 20 40 60 albo 0 40 20 0 Aedes albopictus Albo has no effect on Aeg, so effect of 1 Albo = 0 Aeg Aedes aegypti response Aedes aegypti aeg 20 20 40 60 albo 0 40 20 0 Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg Aedes aegypti response aeg 20 20 40 60 albo 0 40 20 0

  30. Results Aedes aegypti survivorship aeg 20 20 40 60 albo 0 40 20 0 ANOVA: treatment x food x tire(=block) Followed by t-tests (posthoc)

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