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Competition experiments

Competition experiments

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Competition experiments

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  1. Competition experiments

  2. What is competition? What are possible response variables for a competition experiment?

  3. Some possible types of competition questions • Does associate species X affect the growth/fitness of focal species Y? • How does interspecific competition (effect of X on Y) compare to intraspecific competition (effect of Y on Y)? • Is competition asymetrical? That is, does either X affect Y more than Y affect X, or vice versa? • Is the strength of competition dependent on the density of the associate species (X)? Density of the focal species (Y)?

  4. Focal species Additive design Associate

  5. N associate Monoculture of focal N focal species

  6. Substitutive design (replacement series)

  7. Monoculture of associate N associate Monoculture of focal N focal species

  8. Response surface Monocultures of associate N associate Monocultures of focal N focal species

  9. Groups Additive Substitutive Gina Rebecca Heather Aerin Annie David Riann Liz Hillary Marie Nick Aliice Katsky James

  10. What two factors/processes are confounded in your experimental design? • Which type of competition question can your design answer? Which can it not? • How would you analyze results from your experimental design?

  11. Cultural exchange Additive Substitutive Gina Rebecca Heather Aerin Annie David Riann Liz Hillary Marie Nick Aliice Katsky James

  12. What two factors/processes are confounded in your experimental design? • Which type of competition question can your design answer? Which can it not? • How would you analyze results from your experimental design?

  13. Some possible types of competition questions • Does associate species X affect the growth/fitness of focal species Y? • How does interspecific competition (effect of X on Y) compare to intraspecific competition (effect of Y on Y)? • Is competition asymetrical? That is, does either X affect Y more than Y affect X, or vice versa? • Is the strength of competition dependent on the density of the associate species (X)? Density of the focal species (Y)?

  14. Some possible types of competition questions • Does associate species X affect the growth/fitness of focal species Y? Additive • How does interspecific competition (effect of X on Y) compare to intraspecific competition (effect of Y on Y)? • Is competition asymetrical? That is, does either X affect Y more than Y affect X, or vice versa? • Is the strength of competition dependent on the density of the associate species (X)? Density of the focal species (Y)?

  15. Some possible types of competition questions • Does associate species X affect the growth/fitness of focal species Y? Additive • How does interspecific competition (effect of X on Y) compare to intraspecific competition (effect of Y on Y)? Substitutive • Is competition asymetrical? That is, does either X affect Y more than Y affect X, or vice versa? • Is the strength of competition dependent on the density of the associate species (X)? Density of the focal species (Y)?

  16. Some possible types of competition questions • Does associate species X affect the growth/fitness of focal species Y? Additive • How does interspecific competition (effect of X on Y) compare to intraspecific competition (effect of Y on Y)? Substitutive • Is competition asymetrical? That is, does either X affect Y more than Y affect X, or vice versa? L-shaped additive or substitutive • Is the strength of competition dependent on the density of the associate species (X)? Density of the focal species (Y)?

  17. Some possible types of competition questions • Does associate species X affect the growth/fitness of focal species Y? Additive • How does interspecific competition (effect of X on Y) compare to intraspecific competition (effect of Y on Y)? Substitutive • Is competition asymetrical? That is, does either X affect Y more than Y affect X, or vice versa? L-shaped additive or substitutive • Is the strength of competition dependent on the density of the associate species (X)? Density of the focal species (Y)? Additive, response surface

  18. Competition models (two examples) Example 1: Additive series design for container mosquito larvae

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

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

  21. Ranges overlap, potential for interspecific competition

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

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

  24. 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.

  25. 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

  26. 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

  27. 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)

  28. Competition example 2: Tidepool sculpins Oligocottus maculosus Clinocottus globiceps Pfister, C.A. 1995. Estimating competition coefficients from census data: a test with field manipulations of tidepool fishes. Am. Nat. 146: 271-291

  29. Types of response variables: • Static – Within one generation (most studies) • - Difficult to related to population dynamics (ßij) • Dynamic – Differences between generations • - Can calculate ßij directly Lotka-Volterra: dNi/dt= ri Ni [1-Ni/Ki – (ßij Nj)/Ki] Impact of one individual of species i relative to one individual species j

  30. Lotka-Volterra: dNi/dt= ri Ni [1-Ni/Ki – (ßij Nj)/Ki] or Ln[Ni(t+1)/Ni(t)] = ri – (r/ Ki) Ni(t)– (ßij/Ki)Nj(t) Change in species “i” density over time Densities of two species

  31. Lotka-Volterra: dNi/dt= ri Ni [1-Ni/Ki – (ßij Nj)/Ki] or Ln[Ni(t+1)/Ni(t)] = ri – (ri/ Ki) Ni(t)– (ßij/Ki)Nj } } } Change in species “i” density over time slopes intercept

  32. Tidepool sculpins: observed 5 tidepools over 2 years Lotka-Volterra: Ln[Ni(t+1)/Ni(t)] = ri – (ri/ Ki) Ni(t)– (ßij/Ki)Nj } } } Change in density over time of Oligocottus 0 (nonsig) -0.718 (sig) intercept

  33. What Biol 404 students learnt last year: • Two weeks is long enough to get a measure of growth • Lambda is a useful measure of population growth. • Duckweed growth was not strongly impacted by nutrient supply or starting density over 2 weeks. • Duckweed takes a long time to count! But digital images aren’t the answer in the short term • Algae invaded after 1 week, may have impacted growth?

  34. Does algal cover reduce duckweed growth (lambda)? Correlations (not experimental manipulations) for 2 different species

  35. 1. Set-up of pilot experiment. 2. Take down pilot experiment 2 weeks later. 3. Use power analysis to decide on sample sizes for your proposed experiment, using pilot data. 4. Hand in research proposal (based on pilot expt and analysis, but outlines a much more ambitious experiment)