Activity - Island Biogeography1010
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Dec 6, 2023
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Island Biogeography and Biodiversity
The four graphs are due on Blackboard in the AL
folder by the end of class! The graphs are the
three from the prelab and the one from question
7.
Biodiversity is a term used to describe the diversity of life and living systems, and can
be measured at different hierarchical levels. The theory of island biogeography
(discussed in your book pg.1136) explains how the processes of immigration and
extinction lead to stable numbers of species on islands of a given size. A key prediction
of this theory is that islands that are farther away from the mainland (or other sources of
new immigrants) will have a lower species richness compared with an island of the
same size that is closer to the mainland (or other source of immigrants). The prediction
is in the graph below:
Prelab: Using the Plant Species excel data sheet in the Blackboard AL
folder, create the following
three
scatterplots
without
connecting lines.
These must be graphed separately! You should show this to us when you
arrive to class,
and will be asked to leave if it is not done.
●
Island Area vs Species Richness
●
Island Elevation vs Species Richness
●
Distance to Santa Cruz vs Species Richness
1.
Our plant data isn’t distributed normally - You can see your graphs look unusual. To
better visualize our data, we can use
log scales.
This doesn’t change our data, it just
makes it easier to see the relationships. For all graphs, change both axes to
log scale.
To do this, double click on an axis label (one of the numbers; or you can click “Add
Chart Element > Axes > More Axes Options). This will open a window. Under the “Axis
Options” tab (the three bars under “Text Options”), click on “Logarithmic Scale”.
Repeat
this for each axis for all three graphs.
The axes should be similar to what’s below
(but with more data).
2.
Looking at the “
Island Area vs Plant Species Richness
” Graph - Is there a
relationship between species richness and island Area?
-If so, what is the relationship? (
Ex: As area increases, species richness ________)
As area increases, species richness increases.
3.
Looking at the “
Island Elevation vs Plant Species Richness
” Graph - Is there a
relationship between species richness and island elevation?
-If so, what is the relationship? (
Ex: As elevation increases, species richness ____)
As elevation increases, species richness increases
4.
Using
both
the
Island Area
graph and the
Island Elevation
graph, which of the two
seems to better predict the species richness of an island, area or elevation? (Hint: R
2
).
-Explain your answer with references to the graphs.
The R^2 value for Island elevation is 0.54141 and for island area its 0.3797. The R^2
value indicates the strength of the correlation between two variables. Given that island
2
elevation has a higher R^2 value, it appears to be a better predictor of species richness
on an island. Upon examining the graphs, it is evident that there is a notable disparity in
species richness. The island area graph shows a lower degree of distribution per square
kilometer, while the island elevation graph displays a higher concentration of species
distribution per meter. Utilizing elevation as a predictor seems more effective, as using
area would result in a more dispersed dataset compared to the concentrated distribution
seen with elevation.
Area vs Species Richness curves plotted using regular axes scales typically look like
the figure shown below:
Data from http://www.qc.ec.gc.ca/faune/biodiv/en/methods/meth_invert_fish.html
5.
Provide one hypothesis
about why the relationship above might exist, and be sure
to:
-Include why you think there is a relationship between
species richness and area
,
AND
-Define the word
niche
and include it in your answer.
-Why the relationship would take the shape of a
log function
(i.e. a sharp increase at
first followed by a plateau).
As the area of interest increases the diversity of freshwater fishes increases but after a
certain distance the diversity plateaus because of no longer being in the right habitat for
3
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freshwater fish and the increasing diversity of other species as well. This suggests that
larger areas provide more diverse habitats and resources, which supports a greater
number of species. A niche defines to the role or function of an organism or species
within an ecosystem, including how it obtains and uses resources, where it lives also
how it interacts with other species. It essentially the ecological space occupied by a
species in its habitat. The log function shape captures the diminishing returns as
available niches become saturated, leading to a plateau in species richness. This also
shows a pattern of the initial species increase with increased area.
Part II
Now, let's explore this relationship with the Galapagos data set. Go to the excel sheet
entitled "Plant
Species Richness vs. Distance to Santa Cruz
". Santa Cruz is one of
the largest islands and also is in the general center of the islands that were sampled.
Your graph on this page should already be in
log scale
.
6.
Describe the relationship (if any)
between
species richness
and
distance to
Santa Cruz
, and be sure to answer the following in your response:
-Does the data match the predicted relationship between
species richness
and
distance from
Santa Cruz
as predicted by the Biodiversity theory graph at the
beginning of the activity?
-Explain your answer.
According to the graph, there is no correlation between the distance from Santa Cruz
and species richness. This aligns with the hypothesis that islands situated farther from
the mainland would exhibit lower species richness compared to islands of the same size
but closer to the mainland. The data that is plotted supports the hypothesis by proving
that the relationship isn’t at a specific rate of change rather no relationship in between.
7.
Make a new scatterplot of the relationship between species and distance from Santa
Cruz,
but this time only use data from islands that are within 2 km of Santa Cruz.
Add a
power trendline
(This is different than usual! We are
not
using a linear trendline).
8.
Compare the relationship between plant
species richness
and
distance to Santa
Cruz
on this graph (distances 0km to 2km) with the one you used for question 7 (the
graph with all the distances).
-What are the differences and why do you think there is a difference?
-Does this tell you anything about the potential dispersal abilities of plants?
4
-Explain your answers using data.
One of differences is that the graph with all the distances, where there is a greater
degree of dispersal after 2km as opposed to the graph specifically focusing on the 0km
to 2km range. This proves that plants dispersal does vary and won’t always be at a
constant steady growth. This shows that there is no relationship between the two
graphs.
9.
How does this second graph (distances 0km to 2km) compare with the predictions of
the theory of island biogeography?
The new graph covering the 0km to 2km range contradicts the hypothesis that islands
farther from the mainland would exhibit lower species richness compared to islands of
the same size but closer to the mainland. Instead, it indicates that in this scenario the
closer proximity to the island is associated with lower species richness.
The four graphs are due on Blackboard in the AL
folder by the end of class! The graphs are the
three from the prelab and the one from question
7.
5