Competitive Exclusion Instructions: Use the competition model...

Competitive Exclusion

Instructions: Use the competition model (contained in "competition model.xls") to evaluate the scenarios of competition between the Colorado pike minnow and rainbow. For each scenario, use the Excel sheet to enter the values for K, r , and the competition coefficient (α or β) for each population..

As per usual, you will need to work through this assignment in order to successfully answer the day's clicker questions.


Species/population 1 = pike minnow

Species/population 2 = rainbow trout

α = effect of species 2 on species 1

β = effect of species 1 on species 2

1. Which of the following strategies would to increase the population of pike minnow in the Colorado River?

a) Increase r for trout

b) Increase K for trout

c) Increase r for pike minnow

d) Increase K for pike minnow

e) Both c and d

2. You work for the US Fish and Wildlife Service, which wants to maintain populations of endangered fish in the Colorado River. You go out and measure some populations and find the following: the competitive effect of trout on pike minnows equals 1.25, the competitive effect of pike minnows on trout equals 0, the per capita growth rate of pike minnows equals 0.25, and the per capita growth rate of trout equals 0.5. The carrying capacity of a species equals the number of available nesting sites. Currently, the environment contains 500 nesting sites.

You devise a way to introduce artificial nesting, which only pike minnows can use. If you introduce these artificial nesting sites by 50 at a time (leaving the trout nesting sites at 500), how many would you have to introduce for the pike minnow's population to persist?

a) 600

b) 700

c) 800

d) 900

e) 1000

3. Your supervisor makes you remove all of the artificial nesting sites because they are preventing people from rafting on the river. So you decide to save the population of pike minnows by destroying nesting sites of trout. Assume that 500 natural nesting sites exist for pike minnow and 500 exist for trout. If you destroy nesting sites for trout by 50 at a time, how many would you need to destroy to get the pike minnow population to grow? Assume that competition coefficients and per capita growth rates are the same as in question 2.

a) 50

b) 100

c) 150

d) 200

e) 250

4. After leaving the Fish & Wildlife Service, you land a job as a botanist on islands off the coast of California. You are studying an endangered plant species that only grows there and nowhere else in the world. You find these plants are outcompeted by an introduced species from Europe.

You study the populations and find the following conditions:


Carrying capacity (K)

Growth rate (r)

native plant



invasive plant



One of the reasons that native plants are declining is that the invasive plants absorb nitrogen from the soil about twice as fast (α = 2). How much would you need to reduce this competition coefficient to enable the native species to persist? Assume that the native species has no competitive effect of the invasive species (β = 0).

a) 0.25

b) 0.5

c) 0.75

d) 1.0

e) 2.0


1 Attachment
PARAMETERS Do not edit these cells! Genera±on Minnow Trout Pike Minnow r 0.5 1 1 1 Results of the model: K 500 2 1 1 alpha 2 3 2 2 Trout 4 3 2 r 0.25 5 5 2 K 1000 6 7 3 beta 2 7 11 4 8 16 5 9 24 6 10 35 7 11 51 9 12 73 11 13 103 13 14 141 16 15 188 18 16 239 21 17 292 24 18 338 26 19 375 28 20 401 30 21 417 31 22 426 32 23 430 33 24 432 34 25 432 35 26 431 36 0 20 40 60 0 200 400 600 800 1000 1200 Genera±on Popula±on
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