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)