Answers to Figure Legend Questions

FIGURE 23.2 The bar graphs indicate there were about 36 million ha in 1500, 8 million ha in 1935, and 1 million ha in 2004. The annual rate of loss appears to have been greater from 1935 to 2004 (7 million ha lost over 69 years, or approximately 100,000 ha lost per year) than from 1500 to 1935 (28 million ha lost over 435 years, or approximately 64,000 ha lost per year).

FIGURE 23.5 As discussed in Chapter 15, the seeds of many plant species are dispersed by animals that eat their fruit; hence the extinction of many frugivores may have reduced the ability of such plant species to disperse their seeds. Likewise, as also discussed in Chapter 15, many plants are pollinated by animals that visit flowers to collect nectar. Hence, the loss of nectarivores may have reduced the reproductive success of some plant species.

FIGURE 23.6 The “open flower” treatment is the control; results for this treatment indicate the percentage of flowers that currently can produce seeds on island and mainland sites. One experimental treatment was to bag flowers; results from this treatment show the percentage of flowers that produce seed in the absence of bird pollinators and all other means of pollination except self-pollination. A second experimental treatment was to hand-pollinate flowers; results from this treatment show the percentage of flowers that produce seeds when pollination is not limiting (as should be true

when bird pollinators are abundant).

FIGURE 23.8 The difference between this statement and the results in the figure (which show that the introduction of non-native plant species can cause regional plant diversity to increase) is due to a difference in scale. When the introduction of non-native plant species causes the global extinction of one or more plant species, global plant diversity will decline even though regional plant diversity increases.

FIGURE 23.10 Habitat loss is the most important factor affecting terrestrial mammals; overharvesting is also an important threat. In contrast, accidental mortality and pollution are the most important threats affecting marine mammals.

FIGURE 23.12 Individual answers may vary but should include a line of reasoning similar to the following: Although there was year-to-year fluctuation in the cod harvest, overall the catch increased from roughly 100,000 tons caught in 1850 to roughly 300,000 tons caught in 1950. Because the harvest was maintained at these levels for 100 years, this suggests that at about 200,000 tons could have been caught in a sustainable manner.

FIGURE 23.15 Over the past decades habitat loss and pollution have been the primary causes of the loss of biodiversity from terrestrial, aquatic, and coastal habitats, while over-exploitation (hunting and harvesting) has been the largest factor influencing biodiversity in marine biological zones. Looking to the future (arrows) climate change and pollution are forecast to be the largest threats to all biological zones, with habitat loss continuing as a concern as well.