15.16–15.17: Communities can change or remain stable over time.

Most communities change over time. The patterns of succession depend on the rate and magnitude of disturbances.

Question 15.32

In a commensal relationship:

  • a) one species pollinates the other.
  • b) neither species benefits or is harmed, but the community itself benefits.
  • c) one species provides nutrients, usually cellulose, for the other.
  • d) one species benefits while the other neither benefits nor is harmed.
  • e) the “loser” has reduced reproductive output.

Question 15.33

Coevolution:

  • a) is responsible for all the beautiful flowers in the world.
  • b) is responsible for nectar production by plants.
  • c) reveals that both biotic and abiotic resources can serve as selective forces.
  • d) can produce an insect with a tongue as long as its body.
  • e) All of the above are correct.

Question 15.34

The chief difference between primary and secondary succession is that:

  • a) primary succession occurs among the plants in a habitat, whereas secondary succession occurs among the animals.
  • b) primary succession begins with no life and no soil, whereas secondary succession begins with both.
  • c) secondary succession alters the biotic environment, whereas primary succession alters the abiotic environment.
  • d) primary succession occurs more quickly than secondary succession.
  • e) primary succession can occur in terrestrial and aquatic habitats, but secondary succession can occur only in terrestrial habitats.

Question 15.35

Keystone species:

  • a) occur only in intertidal zones.
  • b) play an unusually important role in determining the species composition in a habitat.
  • c) can be removed from a habitat without any impact on the remaining species in the community.
  • d) are producers and therefore usually are plants.
  • e) are more expendable than commensal species, from a conservation perspective.