Indicator species (Encyclopedia of Environmental Issues, Revised Edition)
Certain species of plants and animals exhibit strong responses to particular environmental factors, which are not necessarily human-made or deleterious. Observing these species in the field provides a convenient method for initial detection of factors of interest. Usually direct measurements are necessary if the information is to be used for determining environmental policy. Rather than using single species, many environmental surveys employ groups of species, defined either by taxonomic categories or by form and function, that respond similarly to a given environmental stressor.
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Characteristics (Encyclopedia of Environmental Issues, Revised Edition)
The most useful indicator species in environmental monitoring are those that are cosmopolitan (that is, occur in a variety of habitat types over a wide area), are fairly common, and are easily recognized. Rare and endangered species, and those that are narrowly endemic, make poor indicators. One of the strengths of using indicator species is that it allows a person without extensive training or specialized equipment to survey a large number of sites rapidly and identify those that merit more detailed monitoring. This advantage is lost if a species is rare enough to be absent from sites where no pollution or other degradation is present, or if the species is difficult to recognize in the field.
The more specific the response, the better the indicator. A combination of pollution, physical disturbance, and climate change may be causing a general decline of plants and animals. Under those conditions, an epiphytic lichen that concentrates pollutants from the air would be a good indicator of atmospheric pollution, while an introduced weedy species of herb might be a better indicator of disturbance, and a common native insect would be a better indicator of the overall effect of environmental degradation on food webs. If the mechanism of a pollutant’s action is known, scientists may look for specific metabolic changes in a variety of species.
If a dominant or keystone species also has sensitivities making it a useful...
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Examples in Environmental Monitoring (Encyclopedia of Environmental Issues, Revised Edition)
One of the earliest biological responses to environmental degradation to be recognized was that of epiphytic lichens to industrial air pollution. Lichens, a symbiotic association of a fungus, an alga, and in some cases a cyanobacterium, absorb water and nutrients directly from the air or rainwater. Acid rain, high levels of nitrogen, and heavy metals all affect lichen growth in ways that are quite species-specific. In forested areas such as Central Europe and the northwestern United States, where unpolluted mature forests support a diverse lichen flora, total lichen cover, relative abundance of certain species, and the chemical makeup of lichen thalli all provide a cumulative picture of air quality over a number of years. The cumulative effect is helpful to investigators because continual monitoring of air quality can be prohibitively expensive and pollution is often episodic in nature.
Lichenologists recognized in the nineteenth century that members of the lichen family Stictaceae, which contain cyanobacteria, were very sensitive to air pollution. Only in the early twenty-first century did forest management biologists discover that these lichens are important sources of nitrogen in coniferous forests, and that their conservation is a matter of concern in its own right.
Planktonic organisms, both plants and animals, are useful for monitoring pollution and temperature changes in the oceans. Some...
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Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Conti, M. E., ed. Biological Monitoring: Theory and Applications—Bioindicators and Biomarkers for Environmental Quality and Human Exposure Assessment. Billarica, Mass.: WIT Press, 2008.
Dunne, Niall. “Global Warming. Tracking the Effects of Climate Change on Plants.” Plant and Garden News 18, no. 3 (2003): 1-4.
Jovan, Sarah. Lichen Bioindication of Biodiversity, Air Quality, and Climate: Baseline Results from Monitoring in Washington, Oregon, and California. Portland, Oreg.: Pacific Northwest Forest Experiment Station, 2008.
Spellerberg, Ian F. Monitoring Ecological Change. 2d ed. New York: Cambridge University Press, 2005.
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Indicator Species (Encyclopedia of Science)
Indicator species are plants and animals that, by their presence, abundance, or chemical composition, demonstrate some distinctive aspect of the character or quality of the environment. For example, in areas where metal-rich minerals can be found at the soil surface, indicator species of plants accumulate large concentrations of those minerals in their tissues. Studies have shown levels of nickel as high as 10 percent in the tissues of some varieties of the mustard plant in Russia and as high as 25 percent in the tissues of the Sebertia acuminata from the Pacific island of New Caledonia. Similarly, a relative of the mint plant found in parts of Africa has been important in the discovery of copper deposits. This plant grows only in areas that have up to 7 percent copper in their soil.
More recently, indicator species have begun being used as measures of habitat or ecosystem quality. For example, many species of lichens are very sensitive to toxic gases, such as sulfur dioxide and ozone. These organisms have been monitored in many places to study air pollution. Severe damage to lichens is especially common in cities with chronic air pollution and near large producers of toxic gases, such as metal smelters.
Similarly, certain types of aquatic invertebrates and fish have been surveyed as indicators of water quality...
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Indicator Species (World of Microbiology and Immunology)
Indicator organisms are used to monitor water, food or other samples for the possibility of microbial contamination. The detection of the designated species is an indication that harmful microbes, which are found in the same environment as the indicator species, may be present in the sample.
Indicator organisms serve as a beacon of fecal contamination. The most common fecal microorganism that is used have in the past been designated as fecal coliforms. Now, with more specific growth media available, testing for Escherichia coli can be done directly. The detection of Escherichia coli indicates the presence of fecal material from warm-blooded animals, and so the possible presence of disease producing bacteria, such as Salmonella, Shigella, and Vibrio.
To be an indicator organism, the bacteria must fulfill several criteria. The species should always be present in the sample whenever the bacterial pathogens are present. The indicator should always be present in greater numbers than the pathogen. This increases the chances of detecting the indicator. Testing directly for the pathogen, which can be more expensive and time-consuming, might yield a negative result if the numbers of the pathogen are low. Thirdly, the indicator bacterial species should be absent, or present in very low numbers, in clean water or other uncontaminated samples. Fourth, the indicator should not grow more abundantly than the pathogen in the same environment. Fifth, the indicator should respond to disinfection or sterilization treatments in the same manner as the pathogen does. For example, Escherichia coli responds to water disinfection treatments, such as chlorination, ozone, and ultra-violet irradiation, with the same sensitivity as does Salmonella. Thus, if the indicator organism is killed by the water treatment, the likelihood of Salmonella being killed also is high.
Another indicator bacterial species that is used are of the fecal Streptococcus group. These have been particularly useful in salt water monitoring, as they persist longer in the salt water than does Escherichia coli. In addition, the ratio of fecal coliform bacteria to fecal streptococci can provide an indication of whether the fecal contamination is from a human or another warm-blooded animal.
The use of indicator bacteria has long been of fundamental importance in the monitoring of drinking water. Similar indicator organisms will be needed to monitor water against the emerging protozoan threats of giardia and cryptosporidium.
See also Antibiotic resistance, tests for; Water quality