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Competition experiments

Learn about competition experiments, response variables, and experimental designs for investigations in interspecific and intraspecific competition. Explore questions, designs, and hypothetical scenarios to understand competition dynamics.

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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. Associate species Focal species Resource

  4. Some competition questions • Does associate species X affect focal species Y? • How does interspecific competition (effect of X on Y) compare to intraspecific competition (effect of Y on Y)? • Is competition asymmetrical? 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)?

  5. Focal species Additive design Associate

  6. N associate Monoculture of focal N focal species

  7. Substitutive design (replacement series)

  8. Monoculture of associate N associate Monoculture of focal N focal species

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

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

  11. Some competition questions • Does associate species X affect focal species Y? • How does interspecific competition (effect of X on Y) compare to intraspecific competition (effect of Y on Y)? • Is competition asymmetrical? 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)?

  12. Some possible types of competition questions • Does associate species X affect 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)?

  13. Some possible types of competition questions • Does associate species X affect 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)?

  14. Some possible types of competition questions • Does associate species X affect 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)? L-shaped additive or substitutive

  15. Some possible types of competition questions • Does associate species X affect 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)? Additive L-shaped additive or substitutive

  16. Example: Additive series design for container mosquito larvae

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

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

  19. Ranges overlap, potential for interspecific competition

  20. 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.

  21. 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.

  22. 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.

  23. 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

  24. 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

  25. 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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