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Competition experiments
What is competition?
What are possible response variables for a competition
experiment?
Associate species Focal species
Resource
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)?
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 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
es a
lbop
ictu
s
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
es a
lbop
ictu
s
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
es a
lbop
ictu
s Can asses Aedes aegypti performance in these treatments
Hypotheses:
Aedes aegypti
Aed
es
alb
op
ictu
s
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse
Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse Albo has no effect
on Aeg, so effect of 1 Albo = 0 Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse
Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg
Hypotheses:
Aedes aegypti
Aed
es
alb
op
ictu
s
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse
Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse Albo has no effect
on Aeg, so effect of 1 Albo = 0 Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse
Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg
Hypotheses:
Aedes aegypti
Aed
es
alb
op
ictu
s
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse
Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse Albo has no effect
on Aeg, so effect of 1 Albo = 0 Aeg
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
re
spo
nse
Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg
Results
aeg 20 20 40 60albo 0 40 20 0
Aed
es
aeg
ypti
su
rviv
ors
hip
ANOVA: treatment x food x tire(=block)
Followed by posthoc to find difference between levels