Biology 12

450 MHR • Unit 5 Population Dynamics

SECTION REVIEW

1. Explain why the primary productivity of a
   grassland usually exceeds the primary productivity of
   a forest ecosystem covering an area of the same size.


2. Identify the factors that might cause annual
   fluctuations in the primary productivity of a specific
   grassland ecosystem.


3. On average, less than 20 percent of the food
   energy consumed by a grasshopper is converted into
   new grasshopper tissue. What happens to the rest of
   the food energy that was contained in the tissues of
   the producer species consumed by the grasshopper?


4. Explain why many models showing the
   relationships among trophic levels in an ecosystem
   are shown in the shape of pyramids. Describe the
   difference between the information depicted in a
   biomass pyramid, a pyramid of productivity, and
   a pyramid of numbers.


5. Explain why the primary productivity levels of
   equatorial ecosystems generally exceed those of
   ecosystems situated farther north.


6. Explain why the energy transfer from herbivores
   to carnivores is more efficient than the energy transfer

from producers to herbivores within the same food

chain.

7. Suppose that the biomass for primary
   producers is less than the biomass for primary
   consumers. Can this ecosystem survive? Explain
   your answer.


8. Describe the factors that determine the shape
   of a pyramid of numbers diagram for a specific type
   of ecosystem. Explain why a grassland pyramid
   would have a wider base than a forest pyramid.


9. We have seen that there are fewer carnivores
   than herbivores in ecosystems because of the
   inefficiency of energy transfer between trophic levels,
   and that the world could support more people if we
   ate only plant material. Some people feel this means
   that humans should switch to a vegetarian diet;
   others disagree. There are, in fact, a variety of issues
   to consider in addition to the relatively simple one of
   energy transfer. Take a stand. Prepare your arguments
   carefully and be prepared to debate the issue in
   class. You might want to prepare a pamphlet that
   could be used to educate the public (or the rest of
   the class) about your point of view.

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sea birds

2 800 ppb

fish

43 ppb

squid

22 ppb

plankton

1.7 ppb

seawater

0.0001 ppb

dolphins

5 200 ppb

Figure 13.24An example of data collected on DDT in a food web of organisms in

the north Pacific Ocean. Concentration of DDT is measured in parts per billion

(ppb). The arrows indicate the flow of energy from one trophic level to another.