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Unit 12: Ecology
Possible Free-Response Questions
Answers must be in complete sentences; outline form is not acceptable. Labeled
diagrams may be used to supplement discussion, but in no case will a diagram alone
suffice. It is important that you read each question completely before you begin to write.
1. An energy pyramid for a marine ecosystem is shown below.
a. Label each trophic level of the pyramid and provide an example of a marine
organism found at each level of this pyramid.
b. Explain why the energy available at the top layer of the pyramid is a small
percentage of the energy present at the bottom of the pyramid.
c. Bacteria play central biological roles. Bacteria may act as
 Producers
 Parasites
 Mutualistic symbionts
 Decomposers
Select THREE of the ecological roles above. For each one you choose, describe how
bacteria carry out the role and discuss its ecological importance.
2. Many populations exhibit the following growth curve:
a. Describe what is occurring in the population during phase A.
b. Discuss THREE factors that might cause the fluctuations shown in phase B.
c. Organisms demonstrate exponential (r) or logistic (K) reproductive strategies. Explain
these two strategies and discuss how they affect population size over time.
3. According to fossil records and recent published observations, two species of leaf-eating
beetles (Species A and B) have existed on an isolated island in the Pacific Ocean for
over 100,000 years. In 1964, a third species of leaf-eating beetle (Species C) was
accidentally introduced on the island. The population size of each species has been
regularly monitored as shown in the graph above.
a. Propose an explanation for the pattern of population density observed in species C.
b. Describe the effect that the introduction of beetle species C has had on the
population density of species A and species B. Propose an explanation for the
patterns of population density observed in species A and in species B.
c. Predict the population density of species C in 2014. Provide a biological
explanation for your prediction.
d. Explain why invasive species are often successful in colonizing new habitats.