DescriptionLab Exercise 5
Biogeography
GEOG 121
Name _____________________
Lab section ________________
Lab instructor ______________
Partner ____________________
Points Earned = ____/23
Scaled to 10 = _____/10
In this lab, you will
Measure tree-ring width
Map the range limit for a species
Observe ecoregions
Calculate biodiversity
Describe the latitudinal diversity gradient
Observe global patterns of land use and anthropogenic biomes
Materials
Printed cross-sections of trees
Rulers
Relevant reading
Textbook. Chapter 10. Plant Geography in Discovering Physical Geography
Ellis, E. C. and N. Ramankutty. 2008. Putting people in the map: anthropogenic biomes
of the world. Frontiers in Ecology and the Environment 6 doi:10.1890/070062
McCarroll, D. and N. J. Loader. 2004. Stable isotopes in tree rings. Quaternary Science
Reviews 23: 771-801
Introduction
Biogeography is the study of the spatial and temporal patterns of the distribution of living
organisms on Earth (including plants, animals, and microbes). It also includes
understanding the biological and physical processes responsible for these patterns. The
chapter in the Arbogast textbook is called plant geography, and indeed plants can be
easier to study than other organisms, as they do not move and are visible to the human
eye. However, all organisms have spatial patterns that are studied in the field of
biogeography.
Exercise 1: Local biogeography and tree-rings
“Trees are wonderful things. They stand fixed in the landscape, often for centuries,
making layers of wood laid down in annual succession” (McCarroll and Loader 2004).
The newest (youngest) rings are on the outside adjacent to the bark. The study of tree
rings is generally called dendrochronology (from dendro=tree, chronos=time, and
ology=study of). Dendrochronology is a sub-discipline of geography and relates to
biogeography in several ways.
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1. Choose one of the tree sections. Count the total number of rings. Note the
approximate age (number of rings from the center ring).
Total number of rings: _______________ (1 point)
Note that the tree-rings vary in width.
2. List the factors that could cause variation in ring-width. List as many as you can
think of, but at least 3. (1 point)
3. Measure the first 30 ring widths for your tree ring section. (1 points)
Ring #
Ring width
(mm)
Ring #
Ring width (mm)
Ring #
1
11
21
2
12
22
3
13
23
4
14
24
5
15
25
6
16
26
7
17
27
8
18
28
9
19
29
10
20
30
Ring width
(mm)
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4. Make a graph of the data in excel from step 3. Remember to label axes. Insert the
graph below. (1 point)
5. Based on the graph above describe the growth history for the 30 year period you
plotted. (1 point)
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Exercise 2: The concept of a range limit
The species range limit is a common concept used in biogeography. The range limit is a
very easy concept to describe, yet very difficult to measure (much like the concept of a
species itself). The basic idea is that an organism will be found only in places where its
absolute environmental requirements are met. Here is an example.
Figure 1. The range of sugar maple, Acer saccharum. Source: Atlas of Relations
Between Climatic Parameters and Distributions of Important Trees and Shrubs in North
America by Robert S. Thompson, Katherine H. Anderson, and Patrick J. Bartlein, U.S.
Geological Survey Professional Paper 1650. (Original source: Little 1971)
1. Based on the tree-ring exercise from Exercise 1, list a factor that might be determining
the range limit of sugar maple on its western edge? (hint: look at United States
precipitation and temperature maps, search credible online resources to attain these).
Explain your answer. (1 point)
2. What about the southern edge? Explain your answer. (1 point)
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Here are a few of the more complicated concepts about a species range: genetic
differences within the range, disjunct populations, discontinuous edges, holes, and
differences in abundance throughout the range. There is the additional problem that when
organisms are taken outside their ranges, they can still grow and thrive.
One major example of this is the concept of an invasive species. Species of plants and
animals are being transferred around the Earth at rapid rates by humans, both accidentally
and intentionally. Sometimes when species arrive on a new continent or island, they
thrive and their population size explodes. This can create problems for native species and
ecosystems. Some examples of invasive species causing problems are zebra mussels
(native to Russia) in the Great Lakes of the U.S., the cane toad (native to Central and
South America) in Australia, feral cats in New Zealand which had many species of native
flightless birds, and honeysuckle in Ohio which outcompetes almost all native vegetation.
There is a variety of spatial information available about the ranges of common species.
You may explore some of this information yourself through the Map Of Life website.
Open the following web address https://mol.org/species/. Next change “all groups” to
“mammals” then click on “Pick a random species”. This will select a species for you.
3. What is the Latin name of the species that was selected? (1 point)
4. What is the common name of this species? (1 point)
5. Look at the map. Where, generally, does it live? (1 point)
Select a random species a few more times to explore the home ranges of other interesting
species!
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Exercise 3: Global latitudinal diversity gradient
One of the strongest geographic patterns of life on Earth is what has been called the
latitudinal diversity gradient. Biodiversity is the biological diversity in a place as
indicated by numbers of different species. Biodiversity varies predictably with latitude,
where biodiversity decreases with increasing latitude. You may be familiar with the
concept of tropical biomes having greater biodiversity than temperate biomes.
This strong pattern has been documented and explored by several generations of
biogeographers. Although there are many good hypotheses to explain this pattern, a
complete and simple answer has been elusive.
An additional complicating factor is that we still do not know the total quantity, let alone
the types, of organisms that live on our planet. The number of organisms on Earth is one
aspect of biodiversity.
There are several ways to measure and quantify biodiversity. Let us examine two
common ways to measure biodiversity for a group of organisms (trees) that we
understand fairly well. First, we have to delineate a study area or plot as shown in the
figure below.
Complete the exercise below based on the plot in Figure 2.
40 m
50 m
Figure 2. Example forest with various tree species.
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Calculate the following based on figure 2. Remember to show all your work.
1. Determine the number of species, also known as S = species richness. (1 points)
S=
2. Calculate the area per each unique specie (m2/species). (2 point)
3. Calculate the Shannon-Wiener index value using the equation below.
where S is the total number of species and pi is the frequency of the ith species
(the probability that any given individual belongs to the species, hence p). (3
points)
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Now we are going to calculate S (species richness) across a latitudinal transect.
Table 1. Survey of species presence across a latitudinal transect from Central America to
Northern Canada.
species
tree #1, Engelhardtia mexicana
tree #2, Ficus sp. (fig)
tree #3, Pinus strobus (white pine)
tree #4, Psycotria macrophylla
tree #5, Lauraceae family
tree #6, Dieffenbachia maculata
tree #7, Socratea (palm)
tree #8, Dipteryx panamensis
tree #9, sugar maple, Acer saccharum
tree #10, black spruce, Picea mariana
S (species richness)
3N
x
x
x
x
x
x
15N 33N 45N
x
x
x
x
72N
x
x
x
x
x
x
*Graph the diversity of tree species in excel. The X axis will be latitude, and the Y axis
will be S, species richness. (2 points)
4. Write a hypothesis about what might be causing this pattern. (1 point)
5. How would you test it? Be specific. (1 point)
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Exercise 4: Anthropogenic biomes of Earth
The traditional view of biogeography has emphasized the concept of “potential natural
vegetation.” Thus, we see maps of what type of plants would grow in a place if people
did not live on the Earth. Geographers are increasingly studying the role of human land
use on the Earth’s surface, and some have developed a concept called an “anthropogenic
biome.” The basic idea is to look at the actual land cover on Earth rather than what could
or would potentially be there.
Exercise A: Anthropogenic biomes
Load Google Earth Ellis and Ramankutty “Anthropogenic Biomes” coverage
https://anthroecology.org/anthromes/12kdggv1/maps/ge/. Explore it by spending
a few minutes examining the distribution of anthropogenic biomes across the Earth
through time. You will need zoom in quite a bit to see specific locations. Next answer the
following questions. Hint: You can adjust the transparency on the bottom right of the
map.
1. How many subcategories of anthropogenic biomes are there (e.g. number of specific
colors in the legend)? (1 point)
2. What anthropogenic biome dominated Ohio in 10000 BC (zoom in to see)? How was
it changed by 2017 AD? How do you predict land cover will change in Ohio within
the next 500 years? (1 point)
3. Select a location outside of the United States. What location have you selected?
Which anthropogenic biome is there currently? Which natural biome was there in
10000 BC? (1 point)
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