Page 1 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 definitions 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.
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?
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
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:
b) Example of a state factor:
Biome / Major Characteristics
Chicago, IL / 9 / 89 / Deciduous Forest / Seasonal climate; trees shed leaves; moderate productivity and diversity
Tuscon, AZ / 21 / 22
Tabora, Tanzania / 23 / 87
Toolik Lake, AK / -8 / 18
Beijing, China / 12 / 63
Valdivia, Chile / 13 / 240
Tromso, Norway / 2 / 101
Puntarenas, Costa Rica / 27 / 162
Chanthaburi, Thailand / 27 / 282
Fairbanks, AK / -2 / 27
Champaign, IL / 10 / 100