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We will be completing Assignment 2 – follow all
instructions as given.
Assignment
2: Two Competing Species
As you learned in the background text for
PopEcoLab, interactions between populations of two more different species
(interspecific interactions) can affect population size and population density
in a number of ways that can benefit or harm one or several species. These
assignments are designed to help you learn about interactions that result in
competition by following the population growth of both the brown and blue
sparrow.
- Set the initial number of hawks
to zero. Set the initial population numbers for both the brown and blue
sparrow equal to 200 birds. Set the relative insect consumption by the brown
sparrow equal to zero, and set the relative seed consumption by the blue
sparrow equal to zero. Keep the remaining parameters at their default
values. Run several simulations and get an estimate of the carrying capacity
of each species. Note: You can run ten independent simulations by
going to the Initial Population view and clicking the Multiple Run Mode
button. With this mode, set the number of runs to 10, then run the
experiment.
What did you observe for the carrying capacity of each species?.
- Go to the Competition view
and use the slider to increase the relative insect consumption by the
brown sparrow, then run this experiment.
What happened to the density of the two sparrows? Is there a point at which one
of the two species goes extinct?
Now
reverse the situation and keep the relative insect consumption by the brown
sparrow equal to zero while increasing the relative seed consumption by blue
sparrows. Before you run this experiment, formulate a hypothesis to predict the
results of this experiment.
What happened to the density of the two sparrows? Is that what you expected?
Explain your results.
- Keep the two consumption
rates of resources equal, but gradually increase both. Make sure you run
several simulations for each set of consumption rates.
What happens as you increase the amount of competition between the two species
of sparrows? Explain these results.
- Set both of the relative
consumption rates back to their default value of 0.50. Design
experiments to investigate the effects of resource densities on species
competition, then run these experiments multiple times. Summarize your
results.
Analysis Questions:
- Five similar populations of small, insect eating birds
live in the same spruce forest and apparently coexist. What variables might
you investigate to explain this?
- Competitive exclusion (i.e. the complete extinction of
the weaker competitor) does not always occur among competing populations.
How do the populations coexist?
- Give a HUMAN example that illustrates the concepts of
competition, specialization, and overlapping niches. Explain how your
example illustrates these concepts.