- Tropical rain forests, coral reefs, and islands contain a significant amount of biodiversity that is at high risk of loss. These habitats are highly represented in 25 global biodiversity hotspots that collectively cover only 1% of the Earth's surface, located predominantly near the equator. - MacArthur and Wilson's theory of island biogeography established that the number of species on an island is related to its size and distance from mainland sources of immigrants. This theory helped explain and predict patterns of species diversity on islands. - Preserving keystone species is an effective conservation strategy because their loss can cause major ecosystem changes, significantly impacting biodiversity beyond the single species.

1. CHAPTER 16 “TAKE-HOME MESSAGE” CHALLENGE QUESTIONS
16.1 Biodiversity offers a great deal of medical and economic value, but also offers
non-utilitarian values including aesthetic, symbolic, and naturalistic. What is the
fundamental difference between the two types of value?
Answer: The utilitarian values of biodiversity are quantifiable, and in some ways, far
easier to explain than the considerable non-utilitarian values of biodiversity. This is
especially the case when a discussion of biodiversity is based on an economic issue.
16.2 Biodiversity is most commonly defined as the number of distinct species in a
habitat, though sometimes this is slightly modified to include the number of different
classes or families of organisms. At what levels can biodiversity be considered?
Answer: Biodiversity can be considered at multiple levels, from the ecosystem to
species to genes and alleles.
16.3 Twenty-five diversity hotspots are home to 20% of the world’s species. What
three types of habitats are highly represented among these hotspots? About how much of
the world’s surface do these hotspots cover and where do they tend to be found on the
globe?
Answer: Tropical rain forests, coral reefs, and islands are areas of significant
biodiversity where this biodiversity is at high risk. The 25 hotspots cover only 1% of the
world’s surface and tend to be found in areas nearer to the equator than farther away.
16.4 Describe the two fundamental components of MacArthur and Wilson’s theory of
island biogeography. What was the function of this theory?
Answer: MacArthur and Wilson stated that there is a close relationship between the
number of species inhabiting the island and the island’s area, and that the farther an
island is from the mainland, the fewer species it held. This theory was designed to
explain and predict the patterns of species diversity on islands.
16.5 Describe a hypothetical species that would be at the highest risk of background
extinction in terms of the factors of geographic range, population size, and habitat
tolerance.
Answer: The unfortunate species would have a restricted geographic range, a small
population, and a narrow habitat tolerance.
16.6 Biologists believe we are in the midst of a mass extinction. How is this supported
in terms of historical background extinction rates and the current extinction rates?
Answer: Historical background extinction rates are about one extinction per million
species per year. Current extinction rates are 1,000 times greater or more than this.
16.7 Describe the conditions under which an ecosystem disturbance is reversible.
Answer: Ecosystem disturbances are only reversible when the alteration of the habitat
does not include the complete extinction of any species.
16.8 Use the introduction of the brown tree snake onto the island a Guam in a brief
illustration of the two key characteristics that make an invasive species particularly

2. harmful?
Answer: Guam has no native snakes, and thus, there were no predators to the brown tree
snake in its new habitat—causing their populations to grow unchecked. Because the
native species of birds on Guam had never encountered snakes, they had no mechanisms
to compete with or defend themselves against the snakes. As a result, brown tree snakes
have eradicated most of the native species of birds on Guam.
16.9 What is the key factor that makes acid rain and acid fog more than just a local
phenomenon?
Answer: Wind currents can carry sulfur dioxide and nitrogen dioxide far beyond the
points of their origin.
16.10 Is global warming real, and is it caused by human activities?
Answer: Yes to both. There is no longer any question that human activities contribute
to global warming. The real questions we have to address today concern what the effects
of global warming will be, and what we need to do to stop it.
16.11 Science created the chlorofluorocarbons (CFCs), which have damaged the ozone.
But how does the reduction of CFC production, the stabilization of the atmospheric levels
of ozone, and the potential for full recovery of the ozone by 2065 represent a “success”
for science?
Answer: When CFCs were first introduced, they were considered harmless. Science
identified CFCs as the cause of ozone depletion and helped convince countries of the
world to adopt policies to discontinue the use of CFCs.
16.12 List some of the challenges that must be faced in addressing the problem of
tropical deforestation.
Answer: 1) The most diverse areas must be identified and protected, 2) the poverty that
necessitates the destruction must be dealt with, 3) alternative sources of food and income
must be developed, 4) population growth must be reduced, and 5) education about the
value of preserving biodiversity must be increased.
16.13 Have the effects of the Endangered Species Act been uniformly good?
Answer: No. Though approximately forty species once listed as endangered – including
the bald eagle, the peregrine falcon, the gray whale, and the grizzly bear – have made
remarkable recoveries and have been taken off the list, there have been unintended
adverse outcomes as well. An effect of the ESA is to focus most conservation efforts on
the preservation of individual species and populations, sometimes at the expense of other
elements of biodiversity and sometimes at the expense of efforts to reduce the loss of
ecologically important habitats.
16.14 The preservation of particularly distinctive and charismatic flagship species, such
as the panda or mountain gorilla, can engender significant public support, and preserving
their habitats can serve to preserve many other species as well. Describe one of the other
three strategies targeting individual species for conservation that has been particularly
successful at preserving large amounts of biodiversity beyond that single species.
Answer: 1) Preservation of keystone species is particularly important, since their loss

3. can lead to massive changes in the composition of species in an ecosystem. 2)
Preservation of indicator species, whose presence is an indicator of air or water quality,
helps to preserve conditions that make an ecosystem healthy. 3) The preservation of
wide-ranging umbrella species with large needs for habitat and other resources results in
the protection of numerous other species within the same habitat.