Name______

ALE #7 Ecology

Part I: Ecology General

1.  What is a rain shadow and how is it formed?

(For this answer, I am assuming that winds move from west to east, as they do in the United States). On the west side of a mountain range, the air is accumulating moisture from evaporation over land and water. When this moist air reaches a mountain range, the air is forced upward. As the air rises, it cools, forming precipitation. Most of the moisture from the air falls as precipitation on this western side of the mountain range, leaving little moisture for the eastern side of the mountain range. Thus, the areas just east of a mountain range are in a “rain shadow,” meaning that they have very little moisture. This results in desert or grassland ecosystems.

2.  What is the difference between an ecosystem and a biome?

An ecosystem refers to all of the biotic and abiotic resources of a particular area, whereas a biome is a major type of ecosystem, occupying a large geographic range. Biomes may have several types of ecosystems within them.

3.  Describe the major characteristics and location of the tundra biome.

The tundra is located in areas above the artic circle in the northern hemisphere. The tundra is very cold, and very dry as a result. It has a permanently frozen subsoil (permafrost), which limits the size of the vegetation that can grow there. Thus there are no trees; only grasses and forbs. The treeless landscape allows for very high winds. Plants can only grow there for a short period of time in the summer when a small portion of the topsoil thaws out.

Part II: Population Ecology

4.  What is carrying capacity?

This is the maximum population size that can be supported by the available resources in that population’s environment. Remember that population refer to only one species.

5.  Fill in the following table describing the general characteristics of r-selected and K-selected species:

Characteristic: / r-selected population / K-selected population
Time to maturation (flowering) / quick / slower
Number of offspring per reproduction / as many as possible / few
Annual or perennial? / annual / mostly perennial or biennial
Size of offspring or seeds / small / large
Death rate / very high / low
Life span / short (one season or less – annual) / long (perennial)

Part III: Community Ecology

6.  Contrast primary and secondary succession, giving an example of each.

Primary succession is the change in a plant community over time following the formation of new land, either by glacial retreat or volcanic activity. An example would be: how the plant community at Mt. St. Helens has evolved over time wince 1980. Secondary succession is the change in a plant community over time following any other type of disturbance, such as a fire.

7.  A bear eats wild raspberries in the forest. What type of interaction is this? Explain.

Depends on whether or not the berries are poisonous!! Assuming the berries are not poisonous: Mutualism. The bear is benefiting from the nutrition, and the plant is benefiting from the wide range seed dispersal (as the bear “releases” the seeds over its large habitat range).

8.  Does disturbance increase or decrease diversity? Explain your answer.

Both. With any disturbance, there is typically an initial loss of diversity, in that many organisms/populations may be killed in the disturbance event. If the disturbance is very widespread and catastrophic, there will definitely be a loss of diversity, perhaps for centuries to come. An invasive species or two may take over, resulting in a “permanent” decrease in diversity.

Small-scale, frequent disturbance may actually increase the overall diversity of a community in the long run. For example, a wind storm may knock over a section of trees in a forest, initially killing many of the organisms growing in that section of the forest. This event frees up soil resources and creates an area of sunlight within an otherwise dark forest. This could allow many non-shade tolerant plants to colonize the patch (like prairie plants). Thus, the overall diversity of that forest increased (in terms of species richness).

Part IV: Ecosystem Ecology – How humans affect Earth’s ecosystems

1.  For questions a-d observe the following pyramids with representational data taken from a hypothetical ecosystem. Each level of the pyramid is called a trophic level.

Note: J stands for Joule, a unit of energy and g/m2 = grams per square meter

a.  Consider the pyramid of energy. Starting from the bottom and working your way up, what percentage of energy seems to be passed from one trophic level to the next?

10%

b.  Account for the energy that is not transferred from one trophic level to the next. What happened to all of this energy?

Lost as heat, feces, or not consumed

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