What is an indicator species?

Indicator species are an appealing research and monitoring tool.
Indicator species can signal a change in the biological condition of a particular ecosystem, and thus may be used as a proxy to diagnose the health of an ecosystem.

For example, plants or lichens sensitive to heavy metals or acids in precipitation may be indicators of air pollution.

Indicator species can also reflect a unique set of environmental qualities or characteristics found in a specific place, such as a unique microclimate. However, care must be exercised in using indicator species.

Indicator species are sometimes called proxy or surrogate species.

• In Vancouver, Canada, the environmental health of estuaries is
  monitored by the indicator species of eel grass. In open water
  ecosystems, yellow water lily is the indicator species.
• Salmon are an indicator species for wetland ecosystems of Greater Vancouver as well as over the greater Pacific Rim
• Indicator species for American grassland ecosystems, the five species of prairie dogs now occupy only about 2 percent of their historical range.
• Non-Alaskan grizzly bears are indicator species for mountain
  ecosystems, measuring the health and diversity of the ecosystem.