Answers to Review Questions

1. Commensalism and mutualism share a number of characteristics: they are both very common, they can evolve in many ways, and they can cease to be beneficial if conditions change such that the costs of the interaction exceed its benefits.

2. When a species in a mutualistic interaction provides its partner with a benefit, that action comes at a cost to the species providing the benefit. If circumstances change such that the costs of the interaction are greater than the benefits to one of the species, that species may cease to provide benefits to its partner, or it may penalize its partner. The fact that mutualists may stop providing benefits to their partners when it is not advantageous for them to do so has convinced researchers that mutualism is not an altruistic interaction.

3. Initially, we could expect a decrease in the growth or reproduction of the coral species that are most sensitive to high water temperatures. If high temperatures continued long enough to cause repeated bleaching, it is likely that these more sensitive species would begin to suffer heavy mortality. As a result of the decreased growth, reproduction, and survival of these sensitive species, the species composition of the reef would change: those coral species that were better able to tolerate high water temperatures would constitute an increasingly high percentage of the corals found in the reef. Such changes in the composition of the coral reef community might also affect other species; for example, a fish that depended on an increasingly rare coral for shelter or food might also decline in abundance. As water temperatures continued to rise, other, less sensitive corals might also experience negative effects. Eventually, if temperatures continued to rise, the abundance of all corals in the reef might decline, as would the abundance of the many species that depend on the reef.