Competition experiments
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Competition experiments
Associate species Focal species
Resource
Additive designFocal species
Associate
N associate
N focal species
Monoculture of focal
Substitutive design (replacement series)
N associate
N focal species
Monoculture of focal
Monoculture of associate
N associate
N focal species
Monocultures of focal
Monocultures of associate
Response surface
1. What two factors/processes are confounded in your experimental design?
2. Which type of competition question can your design answer? Which can it not?
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)?
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)?
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)?
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
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
Example:Additive series design for container mosquito larvae
1985
1996
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. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255-268.
Aedes aegypti
Aed
esal
bopi
ctus Substitutive or
replacement series
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
esal
bopi
ctus
Addition design
Experimental design
Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255- 268.
Aedes aegypti
Aed
esal
bopi
ctus Can asses
Aedes aegypti performance in these treatments
Hypotheses:
Aedes aegypti
Aed
esal
bopi
ctus
aeg 20 20 40 60albo 0 40 20 0
Aed
esae
gypt
ire
spon
se Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
esae
gypt
ire
spon
se Albo has no effect on Aeg, so effect of 1 Albo = 0 Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
esae
gypt
ire
spon
se Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg
Hypotheses:
Aedes aegypti
Aed
esal
bopi
ctus
aeg 20 20 40 60albo 0 40 20 0
Aed
esae
gypt
ire
spon
se Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
esae
gypt
ire
spon
se Albo has no effect on Aeg, so effect of 1 Albo = 0 Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
esae
gypt
ire
spon
se Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg
Results
aeg 20 20 40 60albo 0 40 20 0
Aed
esae
gypt
isur
vivo
rshi
p
ANOVA: treatment x food x tire(=block)
Followed by t-tests (posthoc)
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