Unit C – Ecology Week 3
What is Ecology
1. List the six different levels of organization that ecologists study, in order from
smallest to largest.
Individual, population, community, ecosystem, biome, biosphere
2. Describe the three basic methods of ecological research.
Observing involves using the senses to gather information. Experimenting involves
testing hypotheses in a laboratory or natural ecosystem. Modeling involves making
representations of ecological phenomena.
3. Identify two ways in which you interact every day with each of the three parts of the
biosphere – land, water and air.
Student answers should give examples of interactions with land, water and air.
4. Suppose you wanted to know if the water in a certain stream is safe to drink. Which
ecological method(s) would you choose and why?
Most students will choose experimenting, which would involve testing a hypothesis about
whether the water is safe to drink. Some students might choose modeling, which would
involve using a model to investigate whether pollutants or organisms could enter the
water.
5. Give an example of an ecological phenomenon that could be studied by modeling.
Explain why modeling would be useful.
Answers may vary. A typical response might suggest using a mathematical model to
study the effects of global warming on an ecosystem.
Creating a Table
Refer to Figure 3-2, which shows the various levels of organization that ecologists study. In a
table, provide examples of the ecological levels where you live – individuals, populations,
communities and ecosystems – that could be studied by ecologists. Hint: You may wish to use
library resources or the internet.
Energy Flow
1. What are the two main forms of energy that power living systems?
Solar energy is harnessed by autotrophs that conduct photosynthesis. Chemical energy –
the energy within the chemical bonds of inorganic molecules – is harnessed by autotrophs
that conduct chemosynthesis.
2. Briefly describe the flow of energy among organisms in an ecosystem.
Students should describe a one-way flow of energy from autotrophs (producers) to
consumers – first herbivores, and then carnivores and/or omnivores.
3. What proportion of energy is transferred from one trophic level to the next in an
ecosystem?
In general, about 10 percent
4. Explain the relationships in this food chain: omnivore, herbivore and autotroph.
The autotroph is the producer, and it is eaten by the herbivore. The herbivore is then
eaten by the omnivore.
5. Draw an energy pyramid for a five-step food chain. If 100 percent of the energy is
available at the first trophic level, what percentage of the total energy is available at
the highest trophic level?
Students’ pyramids should show 100 percent of the energy available at the first
(producer) level, 10 percent at the second level, 1 percent at the third level, 0.1 percent at
the fourth level, and 0.01 percent at the fifth level.
Interdependence in Nature
Refer to Figure 3-8, which shows a food web in a salt marsh. Choose one of the food chains
within this web. Then, write a paragraph describing the feeding relationships among the
organisms in the food chain. Hint: Use the terms producers, consumers and decomposers in
your description.
What Shapes an Ecosystem
1. What is the difference between a biotic factor and an abiotic factor?
A biotic factor is a living organism. An abiotic factor is nonliving.
2. Name three types of community interactions that can affect an ecosystem.
Competition, predation and symbiosis
3. What is the difference between primary succession and secondary succession?
Primary succession occurs on surfaces where no soil exists. Secondary succession occurs
when a disturbance of some kind changes an existing community without removing the
soil.
4. How is an organism’s niche determined?
An organism’s niche is determined by the physical and biological conditions in its
environment and how it uses those conditions.
5. How are the three types of symbiotic relationships different? Similar?
In mutualism, both species benefit. In commensalism, only one species benefits; the other
is neither helped nor harmed. In parasitism, one species benefits; the other is harmed. In
all three, two species live closely together.
6. Summarize the role of organisms, including micro-organisms, in maintaining the
equilibrium of a marine ecosystem while a dead whale decays on the ocean floor.
Students should describe how scavengers and decomposers eat the decaying meat, how
the decomposition of the whale’s body forms an oasis for sediment dwellers, and how
bacteria decompose the oils inside the whale’s bones.
Creative Writing
Use the information from this section to write a short story about an ecosystem that is disturbed
and undergoes succession. Hint: Include a flowchart with your story to show the main stages of
change.