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Name ________________________
Module 1A: Distribution of the World’s Biomes
Part 1: Introduction to biomes
The broadest classification of Earth’s natural environment is the biome. The exact
terminology may vary, but most biome defenitions divide the earth into about 10 different
familiar ecosystem types such as desert, temperate deciduous forest, tundra, etc. You are
probably already familiar with most biomes, and can picture the different types of plants and
animals that live in each. For instance, how are grassland species different from those of the
boreal forests (a.k.a. “Taiga”) of Canada and Alaska?
Biomes can be defined by the type of plant and animal communities they support.
But what causes each biome to occur where it does on the globe? As it turns out, the location
of biomes can be predicted reasonably accurately by two simple climatic variables:
temperature and precipitation. That is, given the average temperature and precipitation of a
particular place, we can usually guess what type of biome will be found there.
This concept is summarized in the diagram below:
For instance, the average annual temperature of Chicago is about 9°C, and total annual
precipitation is about 90 cm. Based on the chart above, we can see that Chicago is expected
to support a temperate deciduous forest. And, as a matter of fact, the parks and other
protected lands in the Chicago area do support temperate deciduous species.
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Name ________________________
1. Determine the current biome expected for the cities listed in the chart below.
Record your answer in column 3.
2. In addition, briefly describe the major characteristics of the biomes you
identify. You may use your textbook, the internet, or other resources if you are
unfamiliar with the biome.
3. Based on what you know about the locations, are there any on your list that
you think have been predicted incorrectly by the Whittaker diagram?
Most students should be able to guess that the classification of Fairbanks as
Temperate Grassland is incorrect. Fairbanks is in the midst of boreal forest, even
though the Whittaker diagram suggests that it is too dry a location to support that
biome.
Part 2: State Factors and Interactive Controls
Based on the Whittaker diagram, Champaign, IL is expected to support a temperate
deciduous forest biome. Indeed, temperate deciduous trees like oaks and maples today thrive
there, where they have been planted throughout the city. However, when settlers first arrived in
central Illinois, they found the eastern extent of the Great Plains, with few trees naturally
occurring. We know now that this is because frequent lightning-caused fires can maintain a
grassland ecosystem by killing tree seedlings, even in a climate where the trees would
otherwise flourish.
This example highlights an important point. We have already seen that climate alone
can explain much of the pattern of ecosystem distribution across the globe. However,
temperature and precipitation are by no means the only variables that govern ecosystems.
Recall that an ecosystem is defined by all of the interacting biotic and abiotic components of
the environment, and try to come up with a list of at least 10 factors that might influence these
components and thus the type of ecosystem that occurs in any particular place (you know two
already):
3. 10 Factors that influence ecosystem processes
Climate
Fire
Topography, water bodies, species availability, history, soil type, light availability,
seasonality, humans, community composition, competition, predation, invasive
species]
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Name ________________________
As you can see, there are many factors that help define an ecosystem. When studying
ecosystems, it is important to keep this in mind, and to think about the different ways the
factors all interact. While some factors (like climate) play a major role and help classify all
ecosystems into a few general biomes, the complex interactions of unique combinations of
factors ensure that no two ecosystems are exactly alike.
To help think about how ecosystems work, ecologists distinguish between two types of
ecosystem-influencing factors. Interactive controls are a two-way street: they both affect the
ecosystem, and are affected by the ecosystem. Fire is a good example of an interactive
control. Burning obviously affects plant growth, and in turn, the plants produce the fuel which
governs the frequency and severity of natural fires. By contrast, state factors are those factors
that are essentially constant for a given location: they affect the ecosystem, but not the other
way around. For example, climate is considered a state factor because it dictates many
ecosystem processes, but those processes mostly don’t affect the climate.
4. Choose one interactive control and one state factor from your list above, and
elaborate on how they affect ecosystem processes. In addition, describe your
reasoning in classifying each as interactive control vs. state factor.
a) Example of an interactive control:
An interactive ecosystem process is competition, for example. When species
compete for resources, the composition of the ecosystem changes because
some species thrive at the expense of others. This changes other ecosystem
characteristics, like water and nutrient cycling, because different species affect
these processes differently.
b) Example of a state factor:
Topography is an example of a state factor, because it is an important
characteristic of an ecosystem, but it is essentially unaffected by ecosystem
processes.
Page 4
City
Name ________________________
Annual
Annual
Temperature Precipitation
(°C)
(cm)
Predicted
Biome
Major Characteristics
Seasonal climate; trees shed
leaves; moderate productivity and
diversity
Chicago, IL
9
89
Deciduous
Forest
Tuscon, AZ
21
22
Subtropical
Desert
Tabora,
Tanzania
23
87
Savanna
Toolik Lake,
AK
-8
18
Tundra
Beijing, China
12
63
Temperate
Grassland
Valdivia, Chile
13
240
Temperate
Rainforest
Tromso,
Norway
2
101
Puntarenas,
Costa Rica
27
162
Chanthaburi,
Thailand
27
282
Fairbanks, AK
-2
27
Temperate
Grassland
Champaign, IL
10
100
Temperate
Deciduous
Boreal
Forest
Tropical
Seasonal
Forest
Tropical
Rainforest