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FIGURE 9.2 Species diversity as a component of resilience. The Zumwalt Prairie ecosystem in
Oregon contains a high diversity of grasses and wildflowers, including many species of nitrogen-
fixing wildflowers. If one nitrogen-fixing species is eliminated, the lost function can be compensated
for by another nitrogen- fixing species. (Dennis Frates/Alamy)

Support Systems
Natural ecosystems provide numerous support services that
would be extremely costly for humans to generate. One exam-
ple is pollination of food crops (FIGURE 9.3). The American
Institute of Biological Sciences estimates that crop pollina-
tion in the United States by native species of bees and other
insects, hummingbirds, and bats is worth roughly $3 billion
in added food production. In addition to providing habitat
for animals that pollinate crops, ecosystems offer natural pest
control services because they provide habitat for predators
that prey on agricultural pests. Although organic farmers,
who rarely use synthetic pesticides, gain the most from these
pest controls, conventional agriculture benefits as well.
Healthy ecosystems also filter harmful pathogens and
chemicals from water, leaving humans with water that FIGURE 9.3 Support systems. Pollinators such as this honeybee
requires relatively little treatment prior to drinking. With- on a cherry tree play an essential role in ensuring the pollination of
out these water-filtering services, humans would have to food crops. (Steffan & Alexandria Sailer/Ardea/Earth Scenes/Animals Animals)

ModUle 9 ■ Ecosystem Services 107
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