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Competition experiments. What is competition?. What are possible response variables for a competition experiment?. Some possible types of competition questions Does associate species X affect the growth/fitness of focal species Y?

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slide2

What is competition?

What are possible response variables for a competition experiment?

slide3

Some possible types of competition questions

  • Does associate species X affect the growth/fitness of focal species Y?
  • 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)?
slide4

Focal species

Additive design

Associate

slide5

N associate

Monoculture of focal

N focal species

slide7

Monoculture of associate

N associate

Monoculture of focal

N focal species

slide8

Response surface

Monocultures of associate

N associate

Monocultures of focal

N focal species

slide9

Groups

Additive

Substitutive

Gina

Rebecca

Heather

Aerin

Annie

David

Riann

Liz

Hillary

Marie

Nick

Aliice

Katsky

James

slide10

What two factors/processes are confounded in your experimental design?

  • Which type of competition question can your design answer? Which can it not?
  • How would you analyze results from your experimental design?
slide11

Cultural exchange

Additive

Substitutive

Gina

Rebecca

Heather

Aerin

Annie

David

Riann

Liz

Hillary

Marie

Nick

Aliice

Katsky

James

slide12

What two factors/processes are confounded in your experimental design?

  • Which type of competition question can your design answer? Which can it not?
  • How would you analyze results from your experimental design?
slide13

Some possible types of competition questions

  • Does associate species X affect the growth/fitness of focal species Y?
  • 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)?
slide14

Some possible types of competition questions

  • Does associate species X affect the growth/fitness of 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)?
slide15

Some possible types of competition questions

  • Does associate species X affect the growth/fitness of 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)?
slide16

Some possible types of competition questions

  • Does associate species X affect the growth/fitness of 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)?
slide17

Some possible types of competition questions

  • Does associate species X affect the growth/fitness of 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, response surface
slide18

Competition models (two examples)

Example 1:

Additive series design for container mosquito larvae

slide22

Replacement series

Experimental design (Additive series)

Aedes albopictus

Aedes aegypti

Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255-268.

slide23

Addition design

Experimental design (Additive series)

Aedes albopictus

Aedes aegypti

Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255-268.

slide24

Experimental design

Can asses

Aedes aegypti performance in these treatments

Aedes albopictus

Aedes aegypti

Juliano, S. 1998. Species introduction and replacement amongst mosquitoes: interspecific resource competition or apparent competition? Ecology 79: 255-268.

slide25

Hypotheses:

Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg

Aedes aegypti response

aeg 20 20 40 60

albo 0 40 20 0

Aedes albopictus

Albo has no effect on Aeg, so effect of 1 Albo = 0 Aeg

Aedes aegypti response

Aedes aegypti

aeg 20 20 40 60

albo 0 40 20 0

Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg

Aedes aegypti response

aeg 20 20 40 60

albo 0 40 20 0

slide26

Hypotheses:

Albo has an effect on Aeg, and effect of 1 Albo = 1Aeg

Aedes aegypti response

aeg 20 20 40 60

albo 0 40 20 0

Aedes albopictus

Albo has no effect on Aeg, so effect of 1 Albo = 0 Aeg

Aedes aegypti response

Aedes aegypti

aeg 20 20 40 60

albo 0 40 20 0

Albo has an effect on Aeg, but effect of 1 Albo < 1Aeg

Aedes aegypti response

aeg 20 20 40 60

albo 0 40 20 0

slide27

Results

Aedes aegypti survivorship

aeg 20 20 40 60

albo 0 40 20 0

ANOVA: treatment x food x tire(=block)

Followed by t-tests (posthoc)

slide28

Competition example 2: Tidepool sculpins

Oligocottus maculosus

Clinocottus globiceps

Pfister, C.A. 1995. Estimating competition coefficients from census data: a test with field manipulations of tidepool fishes. Am. Nat. 146: 271-291

slide29

Types of response variables:

  • Static – Within one generation (most studies)
  • - Difficult to related to population dynamics (ßij)
  • Dynamic – Differences between generations
  • - Can calculate ßij directly

Lotka-Volterra:

dNi/dt= ri Ni [1-Ni/Ki – (ßij Nj)/Ki]

Impact of one individual of species i relative to one individual species j

slide30

Lotka-Volterra:

dNi/dt= ri Ni [1-Ni/Ki – (ßij Nj)/Ki] or

Ln[Ni(t+1)/Ni(t)] = ri – (r/ Ki) Ni(t)– (ßij/Ki)Nj(t)

Change in species “i” density over time

Densities of two species

slide31

Lotka-Volterra:

dNi/dt= ri Ni [1-Ni/Ki – (ßij Nj)/Ki] or

Ln[Ni(t+1)/Ni(t)] = ri – (ri/ Ki) Ni(t)– (ßij/Ki)Nj

}

}

}

Change in species “i” density over time

slopes

intercept

slide32

Tidepool sculpins: observed 5 tidepools over 2 years

Lotka-Volterra:

Ln[Ni(t+1)/Ni(t)] = ri – (ri/ Ki) Ni(t)– (ßij/Ki)Nj

}

}

}

Change in density over time of Oligocottus

0

(nonsig)

-0.718

(sig)

intercept

slide33

What Biol 404 students learnt last year:

  • Two weeks is long enough to get a measure of growth
  • Lambda is a useful measure of population growth.
  • Duckweed growth was not strongly impacted by nutrient supply or starting density over 2 weeks.
  • Duckweed takes a long time to count! But digital images aren’t the answer in the short term
  • Algae invaded after 1 week, may have impacted growth?
slide34

Does algal cover reduce duckweed growth (lambda)?

Correlations (not experimental manipulations) for 2 different species

slide35

1. Set-up of pilot experiment.

2. Take down pilot experiment 2 weeks later.

3. Use power analysis to decide on sample sizes for your proposed experiment, using pilot data.

4. Hand in research proposal (based on pilot expt and analysis, but outlines a much more ambitious experiment)