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Ray Atkinson
Ray Atkinson, Graduate Student
Category: Homework
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Experience:  Inner-city high school substitute teacher. Degrees in mathemetics, accounting, and education. Years and years of tutoring.
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PopEcoLab - Biology

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Customer: replied 4 years ago.

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

Both carrying capacities will equal approximately 1000

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.


Assignment 3:
Predator and a Prey


Predation is a fact of life. Predators develop abilities to
locate and capture prey, and prey can evolve to develop mechanisms designed to minimize predation. However, if predators are more effective at capturing prey than prey species are at avoiding predation, then the population of prey species will be affected. Conversely, for some species, too little predation can also affect population numbers in a negative way if the prey species population exceeds its carrying capacity.

Evading Predators - Set the initial number of blue sparrows
to zero. We will focus on the population growth of the brown sparrow and the hawk. Set the initial population number for the brown sparrow equal to 200 birds and for the hawk equal to 20 birds. Design experiments to test the effects of increasing flight speed of the brown sparrow. Try several different flight speeds.

What happens? How does increasing
flight speed affect the population numbers of sparrows and hawks?

As sparrow flight speed increases,
eventually hawks become extinct because they are not successful enough at capturing prey.


Design experiments to test the effects of decreasing flight
speed of the brown sparrow.


What happens to the population
numbers of the sparrow and hawk?

The Effect of Clutch Size on Predator-Prey Dynamics - Design
an experiment to test the effects of changing sparrow clutch size on the predator-prey dynamics.


What happens to the population
numbers of the sparrow and hawk as sparrow clutch size increases? What happens when sparrow clutch size decreases?


Design experiments to test the effects of changing hawk
clutch size on the predator-prey dynamics.

What happens to the population
numbers of the sparrow and hawk as hawk clutch size increases? What happens when hawk clutch size decreases?

Paradox of Enrichment - Rosenweig (1972) identified a
phenomenon he called the "paradox of enrichment." He discovered that increasing the carrying capacity of a species‹for example, by adding nutrients to a pond‹can destabilize the system when the species is at risk of predation.
Design experiments to test this idea.


What did you discover? Explain your answers.


Increasing the seed density (carrying capacity) of the brown
sparrow causes predator-prey oscillations of increasingly larger amplitude which eventually results in extinction of the predator and often the prey.


Assignment 4: Two
Competing Prey and a Predator


Ecologists have identified a phenomenon called
"predator-mediated coexistence" (Caswell 1978), where a predator
feeds on a dominant competitor, this allows the weaker competing species to coexist.


Design experiments where the brown sparrow always
outcompetes the blue sparrow in the absence of any hawks, but by adding hawks that feed more heavily on the brown sparrow, all three species coexist.


Were you able to achieve these conditions? Explain your results.


Some predators are "specialists," which survive by focussing on one or a few abundant prey species. Others are "generalists," which need to eat a variety of less common prey to survive.


Design an experiment where a predator is unable to survive
with only one prey source, but can persist when two prey species are available.


Were you able to achieve these conditions? Explain your results.

Ecological systems are complex. Sometimes one species can
indirectly affect another through its effect on a third species.

Design an experiment where hawks eat only brown sparrows
(i.e., blue sparrows have the maximum flight speed needed to avoid hawks) and hawks coexist with brown sparrows when blue sparrows are absent. However, when blue sparrows are present, their competition with brown sparrows is enough to drive hawks to extinction.


What did you discover? What parameters enabled you to create this situation?



I can logically see what the answers would be, but since I do not have access to that program, I cannot prove it.
Good luck with your studies, and I hope that another expert has access to PopEcoLab.
Customer: replied 4 years ago.
if I get you access to the program can you help?
Customer: replied 4 years ago.

Let me see if I can get it to load.

All right, I think I have it working. When is this due, please?
Customer: replied 4 years ago.
I would like to turn in by Thursday
Oh, that is plenty of time. If I can get it running properly, I should be able to get it done by tomorrow latest. I am having some java problems, but I am working through them.
Customer: replied 4 years ago.
That's great thanks so much Ray!
All right, the program is running properly. I'm starting on a Word file for the results. If I have any questions, I will post them here. We'll get this done.

I am done the first question, parts a and b. Part c is going to take some thinking. It is getting late here, so I will pick this up in the morning.

Customer: replied 4 years ago.

ok, no problem thanks

Do you not need assignment 2, question 2?
Customer: replied 4 years ago.
oh sorry, yes I need them all. I'm not sure if my response is right or not
You need the answers to all of the problems listed for assignments 2, 3, and 4, correct?
Customer: replied 4 years ago.
All right. See you tomorrow. Some of the later ones are going to take more time than I thought. Going to take some time to think. Hopefully, I can still get them all done tomorrow.
Customer: replied 4 years ago.
ok great, good night

I believe I have it all done. Please double check for me that I answered all the questions because I worked them out of order. An extra pair of eyes looking at it is always a good idea.

Attachment: 2012-07-10_150628_sparrows.doc

If my answer is complete, please rate my answer.
Customer: replied 4 years ago.
Hi Ray, I'm at work so I'll check the answers tomorrow. Thanks
Fain enough. See you then.
Customer: replied 4 years ago.

Hi Ray,


I just need one thing to be sure everythring is ok. I need each response preceeded by the questions asked. I know it may seem simple but I'm dyslexic therfore I need everything to be in order.




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