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