An indicator species is any living organism that can be used to measure certain environmental conditions. Determining environmental health by indicator species can be achieved by observing and recording factors like population growth, population decrease, and population density. A change in these factors could indicate a change in environmental conditions. These changes could include pollution levels, disease outbreak, climate change, habitat fragmentation, soil contamination, or species competition. Indicator species are sometimes referred to as surrogate species.
As indicator species are uniquely sensitive to changes in ecosystems, they are important management tools for scientists. Researchers have often used indicator species populations as a warning system of impending environmental threats. Through this research, several issues can be identified, including the environmental threat level, its correlation to the ecosystem, and the role of the indicator species within the habitat. In order to effectively utilize indicator species to measure environmental health, the indicator species must also represent other species within the same ecosystem, it must be easy to observe, and it must react consistently to changes in the environment.
Plants, Algae, and Fungi
Plants, algae, and fungi are often used by researchers as indicators species because they can, on most occasions, only be found in specific ecosystems and are sensitive to environmental changes. Moss, for example, can indicate high levels of acidity in the soil, which in turn may indicate acid rain. Fungi is useful for measuring health of old-growth forests. The diversity of wood-decay eating fungi correlates to the diversity of insects in a shared habitat. Additionally, dense populations of fungi within a forest may be indicative of a habitat free of human disturbance.
Fish are also considered indicator species. This is particularly true of salmon and their relationship with the wetland eco-regions of the Pacific Northwest region of North America. These fish are sensitive to water pollution, deforestation, water dams, river channels, and urban growth. As such, they are listed as "at risk" by the National Wildlife Federation.
Amphibians, particularly tree frogs, have long been used as symbols of environmental conservation because of their importance as indicator species. Adult amphibians, for example, share a similar characteristic that makes them responsive to changes in their surrounding ecosystem: moist and permeable skin. Amphibian skin is susceptible to absorbing environmental pollutants, which can originate in either terrestrial or aquatic environments. These pollutants usually come from 3 specific industries: pharmaceutical, agricultural, and manufacturing.
A wide variety of mammals, from large to small, have been used as indicator species for environmental threats across a number of ecosystems. For example, the population size of 5 species of prairie dogs has been used as a health indicator of grassland ecosystems. These habitats are threatened by contaminants such as pesticides used in agriculture and these contaminants go on to negatively affect the health of prairie dogs. Today, these species can only be found in roughly 2% of what was once their original range. For mountain ecosystems in North America, the grizzly bear is an important indicator species. The Dominion Park Service in Canada uses the health of the grizzly bear population to determine if the ecosystem is thriving or at risk.