CH. 8

Question 1

Prediction #1:

Answer 1

The species with the lowest equilibrium resource requirement (R*) will exclude all other competing species.

see graph

Question 2

Testing Prediction #1

Answer 2

Have to measure each species’ R, this requires two steps…
Growing species in monoculture on the resource and measuring the resource concentration when the consumer and resource are at steady state
Calculation of R from the species growth
Next, grow species in mixture and allow to compete, observe extinction/species declines - theory predicts the species with the lowest R* will win

Question 3

constant mortality rate is not

Answer 3

density dependent

Question 4

Miller et al. 2005

Answer 4

xamined a smaller number of studies & concluded the results were mixed, theory had been insufficiently tested

Question 5

Wilson et al. 2007

Answer 5

summarized results from 43 laboratory studies of phytoplankton, zooplankton, & bacteria - concluded 41 were consistent with the R* prediction

Question 6

Tilman & Wedin (1991); Wedin & Tilman (1993)

Answer 6

Only known set of field experiments
Grew five perennial grass species in monoculture, measured R* for nitrogen soil content
Conducted pairwise growth experiments
All resulted in support for the prediction that the species with the lowest R* won

Question 7

Prediction #2:

Answer 7

What two species compete for two limiting resources there are four potential outcomes, one being stable coexistence.

Question 8

Empirical Studies that tested prediction #2

Answer 8

Tested in multiple experiments with phytoplankton and zooplankton (e.g. Tilman 1977, 1981; Kilham 1986; Sommer 1986; Rothaupt 1988, 1996; reviewed in Wilson 2007).
All found support for prediction #2. (See next slide for data)

Question 8

One field experiment conducted by Dybzinski and Tilman (2007), ( prediction 2)

Answer 8

utilized six perennial grasses competing for nitrogen AND light. In six of the eight pairwise combinations the species with the lowest R* won, species coexistence was predicted and observed in two of the eight pairwise combinations.
The reasons for coexistence (tradeoffs?) were not identified.

Question 9

a theory is

Answer 9

an explanation of observed phenomenon or data.

Question 9

Recall that the first experiments of the competitive exclusion principle (first tested by Gause) repeatedly found that

Answer 9

in simple, homogeneous environments species exclude one another, so that there is nearly always a single winner.

Question 10

a verbal hypothesis - is the

Answer 10

the first step to providing an explanation for the phenomenon in nature.

Question 11

Testing the hypothesis can involve many subsequent steps that fall into three categories…

Answer 11

Translation of the verbal hypothesis into a set of mathematical equations.

Controlled testing of the predictions in a laboratory or greenhouse where conditions can be matched to the mathematical theory’s assumptions.

Testing or observation of phenomenon in the field. This allows us to determine if the theory validly reflects observed phenomenon in nature.

Question 12

Nature can vary

Answer 12

dramatically over space and time.

Question 13

why are long term field studies are necessary for natural variation

Answer 13

Competition may take multiple generations to play out

Question 14

Changes in a species’ diet or habitat use in the absence or presence of a competitor are referred to as

Answer 14

niche shifts.

Question 15

Niche shifts may occur for other reasons besides interspecific competition.

Answer 15

see graphs

Question 16

making mathematical equations does what 3 things?

Answer 16

This does three things:
It makes clear the assumptions that underlie the verbal model
It allows us to express the theory in a way that illuminates its properties and accurately state predictions
It may also lead to other insights (i.e. how do fluctuating environmental parameters alter the predictions?)