Puru Singh - Lab 8_ 1403 F23 Island Biogeography Answer Sheet
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GEOG 1403 Fall 2023
Laboratory 8 Answer Sheet:
Island Biogeography
Lab Section:
Name, Partner 1: Puru Singh
Name, Partner 2:
Insert your signature images here:
Statement of Academic Integrity:
By including my typed name and an image of my signature above, I
hereby affirm that this digital assignment submission represents my own original work, completed during
the Fall 2023 semester, did not draw on work submitted by me or another student in a previous semester,
does not include text copied verbatim from an internet source, and was completed in accordance with the
UMN Student Conduct Code
.
Assignment
A. Access the Island Biogeography spreadsheet (found on the assignment page or
here
). This file
represents the island biogeography model as put forth by MacArthur and Wilson during the 1960s (in sort
of a simplified way). You need not worry too much about the numbers at this point; they are there simply
to generate the initial graphics. Instead, pay attention to the structure of the graph as you change several
parameters.
B. This spreadsheet essentially models immigration and extinction rates as a function of island size and
distance. You do not need to worry about the mechanics that go into the calculations, but simply pay
attention to how the rates of immigration and extinction change as you modify a few simple parameters
(area and distance, cells C7 and C8). The initial settings should be as follows:
Initial Parameters
Species pool on mainland (P)
1000
Area of Island (A)
100
Distance from Mainland (D)
300
Colonization Probability(c )
0.20
Extinction Probability (q)
0.20
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GEOG 1403 Fall 2023
The Effect of Island Size
1. When island size is 100 and distance is 300, what is the equilibrium number of species (the number of
species where the two lines cross)?
The equilibrium number of species is around 513.
2. Change island size to 10 and hit return.
A. What happens to the rate of immigration? Describe how the line on the graph shifts.
The rate of immigration decreases, with a shift downwards on the graph.
B. What happens to the rate of extinction? Describe how the line on the graph shifts.
The rate of extinction increases, with a shift upwards on the graph.
C. What is the new equilibrium number of species (estimate to the nearest 10)?
The new equilibrium number of species is 372.16. Rounded to the nearest 10, it’s roughly 370.
3. Change island size to 200 and hit return.
A. What happens to the rate of immigration? Describe how the line on the graph shifts.
The rate of immigration stays the same, the line does not shift.
B. What happens to the rate of extinction? Describe how the line on the graph shifts.
The rate of extinction decreases, with a shift downwards on the graph.
C. What is the new equilibrium number of species (estimate to the nearest 10)?
The new equilibrium number of species is 556.25. Rounded to the nearest 10, it’s roughly around
560.
The Effect of Distance
Reset the area and distance parameters to the original settings (distance=300, size=100)
4. Change distance to 500 and hit return.
A. What happens to the rate of immigration? Describe how the line on the graph shifts.
The rate of immigration decreases, with a shift downwards on the graph.
B. What happens to the rate of extinction? Describe how the line on the graph shifts.
The rate of extinction stays the same, the line does not shift.
C. What is the new equilibrium number of species (estimate to the nearest 10)?
The new equilibrium number of species is 387.43. Rounded to the nearest 10, it’s roughly around
390.
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GEOG 1403 Fall 2023
5. Change distance to 100 and hit return.
A. What happens to the rate of immigration? Describe how the line on the graph shifts.
The rate of immigration increases, with a shift upwards on the graph.
B. What happens to the rate of extinction? Describe how the line on the graph shifts.
The rate of extinction decreases, with a shift downwards on the graph.
C. What is the new equilibrium number of species (estimate to the nearest 10)?
The new equilibrium number of species is 759.75. Rounded to the nearest 10, it’s roughly around
760.
6. Consider the island-mainland configuration depicted below. Using the island biography model
embedded in the spreadsheet, estimate the equilibrium number of species (read along the x-axis where the
immigration and extinction curves cross) for the distance and size characteristics. Fill the values into the
associated table and then answer question 7.
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GEOG 1403 Fall 2023
Table of island parameters.
Area (ha)
Distance (km)
Species Richness (number)
Island A
600
300
622.61
Island B
170
140
720.61
Island C
60
250
526.80
Island D
630
400
556.05
Island E
60
180
607.26
7. Do you note any disparities in the relationships above? That is, are there instances where the number
of species on an island seems larger/smaller relative to its size/distance? How might you explain these
disparities?
I notice that the general richness of the species seems to increase when Area and Distance share a
similar number range. Based on the data, it seems that area plays a bigger role in species richness
than distance does, not by a lot but by a decent margin. Islands A and D both have a larger size
than species on the island but Islands B, C, and E have more species than size. I would expect the
species on islands B, C, and E to be rather small and not take up a lot of space, as there are more
species than the size/distance, and vice versa.
8. Suppose you were responsible for designing a conservation plan for a large area (10s of thousands of
acres, suppose it is in central Alaska) that required you to build in timber harvesting and oil extraction
(which would mean large areas of disturbed land). You have been charged with maintaining biodiversity
to the extent that it is possible. How might you use some of the concepts of island biogeography to help
you plan your conservation efforts, assuming your goal is to preserve some semblance of an intact biota?
I would make sure to keep evolution in the back of my mind. Evolution would probably be the most
helpful concept with the large areas of disturbed land. This is because the animals will need to
adapt to these new places. This in turn will also increase biodiversity. Through immigration, there
will be other resources available for the current organisms in the area to survive on. This will help
keep the intact biota preserved and save some semblance of it. I would also use the base model of
Island B to help form the "blueprint" of this area, only to a much larger extent. I will need to have
the required land for the oil extraction but not interfere with any biodiversity. To do this, I will
make weekly ecological assessments.
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