Chapter 18
1. The total amount of energy fixed by autotrophs in an ecosystem is called
________________.
Answer: gross primary production
2. Net primary productivity is the primary productivity of an ecosystem, after subtracting
energy lost in
a) dead plant tissues.
b) inedible plant tissues.
c) respiration by primary producers.
d) respiration by primary consumers.
e) inefficiencies of photosynthesis.
Answer: C
3. Primary producers make up the first, or basal, ____________ in most food webs.
Answer: trophic level
4. Carnivores that feed on herbivores (or on detritivores) are referred to as
a) primary producers.
b) primary consumers.
c) secondary consumers.
d) parasitoids.
e) keystone species.
Answer: C
5. “Actual evapotranspiration” for an ecosystem refers to the amount of water that
a) is taken up from soils by plant roots.
b) evaporates from soils.
c) is transpired by plants.
d) evaporates from soils plus the amount transpired by plants.
e) could evaporate from soils, if they were kept wet at all times.
Answer: D
6. The terrestrial ecosystems with highest primary production are usually those that are
a) warm and wet.
b) warm and dry.
c) cool and wet.
d) cool and dry.
e) intermediate in both temperature and moisture.
Answer: A
7. Leibig’s “Law of the Minimum” stated that
a) the lowest primary productivity occurs in the coldest ecosystems.
b) primary productivity is typically controlled entirely by climate.
c) primary productivity is typically controlled by both climate and soil nutrients.
d) a single soil nutrient typically limits primary productivity.
e) the highest primary productivity occurs at the lowest trophic level.
Answer: D
8. The low productivity of arctic tundra ecosystems results
a) entirely because tundra has low evapotranspiration.
b) entirely because tundra soils are low in nutrients.
c) entirely because tundra soils retain water poorly.
d) because tundra soils have low nutrients and retain water poorly.
e) because tundra has low evapotranspiration and low-nutrient soils.
Answer: E
9. Among lakes, primary productivity seems to be mainly controlled by levels of
a) light.
b) nutrients.
c) temperature.
d) pollutants.
e) none of the above
Answer: B
10. Among marine systems, primary productivity is highest in tropical portions of the
major oceans, far from terrestrial influences.
Answer: F
11. The major source of nutrients in surface waters of the open ocean is
a) mixing of subsurface with surface waters.
b) deposition from the atmosphere.
c) addition by ocean currents bringing nutrients from nearshore waters.
d) decomposition of dead organic material.
e) photosynthesis by planktonic algae.
Answer: A
12. Experimental fertilizations in the Baltic Sea suggest that primary productivity there is
normally limited by
a) phosphorus.
b) nitrogen.
c) iron.
d) potassium.
e) temperature.
Answer: B
13. The influences of nutrients and temperatures on ecosystem properties are part of what
ecologists call “bottom-up controls.”
Answer: T
14. The “trophic cascade hypothesis” emphasizes the role of
a) nutrients in controlling primary productivity.
b) nutrients in controlling primary consumption.
c) grazing by herbivores in controlling primary productivity.
d) grazing by herbivores in controlling ecosystem nutrient levels.
e) primary productivity in controlling primary and secondary consumption.
Answer: C
15. In Stephen Carpenter and colleagues’ manipulations of lake food webs, increased
densities of adult largemouth bass led to
a) increased rates of grazing on phytoplankton by zooplankton.
b) decreased rates of grazing on phytoplankton by zooplankton.
c) increased population sizes of planktivorous fish.
d) increased consumption of zooplankton by planktivorous fish.
e) no noticeable effects on food web structure.
Answer: A
16. On the Serengeti plain of eastern Africa, large grazing mammals consume what
fraction of total primary production?
a) a negligibly small amount
b) about 10%
c) about 25%
d) about 66%
e) nearly all
Answer: D
17. On the Serengeti plain of eastern Africa, intensive grazing by large mammals greatly
decreases primary productivity in the grazed areas.
Answer: F
18. In Hubbard Brook Experimental Forest, the largest “standing stock” of energy is
represented by biomass of
a) living plant tissues.
b) dead plant tissues.
c) invertebrate herbivores.
d) vertebrate herbivores.
e) vertebrate carnivores.
Answer: B
19. In Hubbard Brook Experimental Forest, the fraction of available solar energy fixed by
primary producers is
a) approximately 2%
b) approximately 15%
c) approximately 50%
d) nearly all of it
e) primary produces do not fix solar energy
Answer: A
20. Nitrogen stable isotopes are useful tools for the study of food web structure because
isotope ratios
a) change in predictable ways across trophic levels.
b) often vary among alternative food sources for a consumer.
c) for a predator exactly match the isotope ratio in its prey.
d) both (a) and (b)
e) both (b) and (c)
Answer: D
21. An increase about 1,000 years ago in 13C content of human collagen from
archeological sites in eastern North America probably records
a) replacement of vegetables and grains in the diet by meat.
b) replacement of corn by beans and squash in the diet.
c) increasing consumption of corn.
d) increasing levels of 13C in soils.
e) increasing levels of 13C in the atmosphere.
Answer: C