Competition experiments What is competition What are possible

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)?

Focal species Additive design Associate

N associate Monoculture of focal N focal species

Substitutive design (replacement series)

Monoculture of associate N associate Monoculture of focal N focal species

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

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? L-shaped additive or substitutive • 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? L-shaped additive or substitutive • Is the strength of competition dependent on the density of the associate species (X)? Density of the focal species (Y)? Additive

Example: Additive series design for container mosquito larvae

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

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

Ranges overlap, potential for interspecific competition

es or eri e iv t s ut en tit m bs ce Su pla re Aedes albopictus Experimental design (“Additive series”) Aedes aegypti Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255 -268.

Aedes albopictus Experimental design (Additive series) Addition design Aedes aegypti Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255268.

Aedes albopictus Experimental design Can asses Aedes aegypti performance in these treatments Aedes aegypti Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255268.

Aedes aegypti response Hypotheses: 40 20 60 0 Aedes aegypti response Aedes aegypti 20 40 aeg 20 albo 0 Albo has no effect on Aeg, so effect of 1 Albo = 0 Aeg 20 40 40 20 60 0 Aedes aegypti response Aedes albopictus aeg 20 albo 0 Albo has an effect on Aeg, and effect of 1 Albo = 1 Aeg aeg 20 albo 0 Albo has an effect on Aeg, but effect of 1 Albo < 1 Aeg 20 40 40 20 60 0

Aedes aegypti response Hypotheses: 40 20 60 0 Aedes aegypti response Aedes aegypti 20 40 aeg 20 albo 0 Albo has no effect on Aeg, so effect of 1 Albo = 0 Aeg 20 40 40 20 60 0 Aedes aegypti response Aedes albopictus aeg 20 albo 0 Albo has an effect on Aeg, and effect of 1 Albo = 1 Aeg aeg 20 albo 0 Albo has an effect on Aeg, but effect of 1 Albo < 1 Aeg 20 40 40 20 60 0

Aedes aegypti survivorship Results aeg 20 albo 0 20 40 40 20 60 0 ANOVA: treatment x food x tire(=block) Followed by t-tests (posthoc)