Chapter 12

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Chapter 17
1. Ecologists summarize feeding interactions among species in a community when they
compile a _________.
Answer: food web
2. Teja Tscharntke’s studies of the food web associated with Phragmites reeds revealed
that
a) only a single parasitoid species can persist exploiting a single species of herbivore.
b) only a single herbivore species can persist attacking a single species of plant.
c) predation by birds actually protects herbivores, because the birds feed on parasitoidinfested herbivore galls but uninfested galls.
d) within local food webs, all interactions tend to be of roughly the same strength.
e) recognizing variation in interaction strength can greatly simplify the depiction of a
food web.
Answer: E
3. A keystone species is one
a) that makes up a very large proportion of total community biomass.
b) that feeds on a very large fraction of all available prey species.
c) that is fed on by a very large fraction of all predators in its community.
d) whose feeding activities have a disproportionate effect on the structure of its
community.
e) that occupies the lowest level (the base) of the food web.
Answer: D
4. In zooplankton and intertidal communities, as the overall diversity of the food web
increases, the proportion of predators in the web
a) tends to decrease.
b) tends to increase.
c) first decreases, then increases again.
d) first increases, then decreases again.
e) stays about the same.
Answer: B
5. In Robert Paine’s studies of the Washington intertidal community, which organism
proved to be a keystone species?
a) the whelk Thais
b) acorn barnacles
c) chitons
d) the starfish Pisaster
e) limpets
Answer: D
6. Removal of Pisaster starfish in the Washington intertidal leads to a decline in diversity
of other invertebrate species.
Answer: T
7. In the Washington intertidal community studied by Robert Paine, the most important
limiting resource is
a) space.
b) light.
c) plankton.
d) nitrogen.
e) water.
Answer: A
8. In Jane Lubchenko’s tidepool system, removal of the herbivorous snail Littorina led to
a) dominance of the tidepools by the unpalatable alga Chondrus.
b) replacement of Chondrus by the more palatable alga Enteromorpha.
c) replacement of Chondrus by other algae better adapted to herbivory.
d) replacement of Enteromorpha by other algae that are better competitors.
e) no marked change in the algal community.
Answer: B
9. Which statement best sums up the relationship between density of the herbivorous
snail Littorina and the diversity of algae in its habitat?
a) highest diversity when Littorina are abundant, in all habitats
b) highest diversity when Littorina are rare, in all habitats
c) highest diversity when Littorina densities are intermediate, in all habitats
d) highest diversity in tidepools when Littorina are rare, but in emergent habitats when
Littorina densities are intermediate
e) highest diversity in tidepools when Littorina densities are intermediate, but in
tidepools when Littorina are rare
Answer: E
10. Keystone species
a) appear to be common in terrestrial systems, but not in aquatic ones.
b) appear to be common in both terrestrial and aquatic systems.
c) appear to be common in aquatic systems, but not in terrestrial ones.
d) by definition, cannot occur in aquatic systems.
e) by definition, cannot occur in terrestrial systems.
Answer: B
11. In Swedish and North American forests, the exclusion of birds from small forest plots
a) suppressed insectivorous reptiles and therefore led to increased insect densities.
b) led to higher insect densities, and therefore enhanced plant pollination.
c) lowered densities of insect herbivores, and therefore reduced leaf damage to shrubs.
d) increased densities of insect herbivores, and therefore increased leaf damage to shrubs.
e) increased densities of insect herbivores, but with no detectable consequences for
plants.
Answer: D
12. We can infer a statistically significant difference between two population means
when, approximately,
a) our estimates of the two means are different.
b) the variances of the two means do not overlap.
c) the standard deviations of the two means do not overlap.
d) the 95% confidence intervals for the two means do not overlap.
e) the 95% confidence intervals for the two means are of different widths.
Answer: D
13. Which statement about Nile perch in Lake Victoria is most likely true?
a) Nile perch are native to Lake Victoria.
b) Introduction of Nile perch to Lake Victoria increased fish diversity in the lake.
c) Introduction of Nile perch to Lake Victoria wiped out all native fish species in the
lake.
d) Introduction of Nile perch to Lake Victoria immediately decreased fish diversity in the
lake.
e) Introduction of Nile perch to Lake Victoria decreased fish diversity in the lake, but
only after many years of no apparent effect.
Answer: E
14. Cleaner wrasse are mutualists of other coral reef fishes. What benefit do they provide
to those other fish?
a) They suppress diseases because they consume carcasses of dead fish.
b) They keep water oxygenated because they consume organic debris before it can rot.
c) They keep fish relatively free of externally-feeding parasites.
d) They maintain fish habitat by keeping corals free of encrusting algae.
e) They reduce fish mortality by repelling large vertebrate predators.
Answer: C
15. The presence of cleaner wrasse enhances diversity of fishes on coral reefs.
Answer: T
16. Invasive Argentine ants have an important effect on community structure of the South
African fynbos because
a) they do not disperse seeds, while native ants do.
b) they disperse seeds more effectively than do native ants.
c) they disperse seeds in different spatial patterns than do native ants.
d) as keystone species, they greatly increase the local diversity of native ants.
e) Argentine ants have invaded many communities, but not the South African fynbos.
Answer: A
17. The impact of Argentine ants on species diversity in the South African fynbos is most
dramatic following fires
Answer: T
18. Human hunters in the Amazon rain forests kill
a) large numbers of almost every mammal and bird species, for food and for skins.
b) large numbers of the smallest mammal and bird species, which are easiest to catch.
c) large numbers primarily of the largest mammal and bird species.
d) large numbers of mammals and birds, but do not greatly affect population densities.
e) only a few mammals and birds, but because humans are keystone species, these few
kills greatly reduce population densities.
Answer: C
19. The use of predaceous weaver ants to control pest insects in citrus orchards was first
recorded in
a) California in the 1950s.
b) Florida in the 1920s.
c) Mexico in Mayan times.
d) China in the 17th century.
e) China in the 4th century.
Answer: E
20. Weaver ants provide effective protection of citrus trees because they
a) remove harmful soft-scale insects (mealybugs).
b) remove all plant-feeding insects.
c) cultivate soft-scale insects, but do not allow them to feed on the trees.
d) cultivate soft-scale insects, but still allow them to be attacked by parasitoids and
predators.
e) none of the above
Answer: D
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