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An indicator species is any biological species that defines a trait or characteristic of the environment. For an example, a species may delineate an ecoregion or indicate an environmental condition such as a disease outbreak, pollution, species competition or climate change. Indicator species can be among the most sensitive species in a region, and sometimes act as an early warning to monitoring biologists. Animal species have been used for indicators for decades to collect information about the many regions. Vertebrate are used as population trends and habitat for other species. Species identification is very important for the conservation of biodiversity. Approximately 1.9 million species have been identified, but there are 3 to 100 million species. Some of them haven’t been studied. There are new species every year that are unknown and are still being discovered each year.〔(【引用サイトリンク】url=http://www.britannica.com/EBchecked/topic/286117/indicator-species )〕 Indicator species serve as measured environmental conditions. Indicator species are also known as sentinel organisms, i.e. organisms which are ideal for biomonitoring. Organisms such as oysters, clams, and cockles have been extensively used as biomonitors in marine and estuarine environments. For example, the Mussel Watch Programme is a world-wide project using mussels to assess environmental impacts on coastal waters. Their well-documented feeding habits, stationary condition and their role as integral parts of the food chain are some of the main reasons why oysters and mussels are widely used biomonitors. A considerable amount of contaminant concentrations are found in the surficial sediments (i.e. the finer-grained particulate matter, usually muds, silts or clays) of marine and estuarine environments. A major physical process governing the transport of fine particulate material and associated particle-bound contaminants in estuarine environments is resuspe nsion. Strong winds create surface waves, which, in shallow water (<5m), project energy to the water-sediment interface resulting in resuspension of fine sediment from the upper layers of the estuary floor. Once in suspension, fine material may be transported by tidal currents to other parts of the estuary and possibly to the ocean during multiple reworking phases. Mussels and oysters are filter feeders and therefore uptake is by ingestion of particulates in the water column. Sediment resuspension is thus very important in the bioaccumulation process which aids the evaluation of possible adverse biological effects of sedimentary contaminants in marine and estuarine environments. ==Examples== * Stoneflies: indicate high oxygen water : Stoneflies spend the majority of their live as nymphs. Many species require a high concentration of dissolved oxygen and are found in clean swift streams with gravel or stone bottom. * Mosses: indicate acidic soil〔http://www.britannica.com/EBchecked/topic/286117/indicator-species〕 * Greasewood: indicates saline soil : Greasewood grows on dry, sunny flat valley bottoms on ephemeral stream channels. It is one of the dominant plants throughout Great Basin and Mojave Desert. In high saline areas, greasewood grows in nearly pure stands.〔http://www.britannica.com/EBchecked/topic/286117/indicator-species〕 * Lichens: some species indicate low air pollution : Lichens as a group have a worldwide distribution and grow almost on any surface, for example soil, bark, roof tiles or stone. Because lichens get all their nutrients from the air, many species are very sensitive to air pollution. * Mollusca: numerous bivalve molluscs indicate water pollution status : Mollusca, and quite often bivalve molluscs are used as bioindicators to monitor the health of an aquatic environment, either fresh- or seawater. Their population status or structure, physiology, (behaviour ) or their content of certain elements or compounds can reveal the contamination status of any aquatic ecosystem. They are extremelly useful as they are sessile - which means they are closely representative of the environment where they are sampled or placed (caging) -, and they are breathing water all along the day, exposing their gills and internal tissues: bioaccumulation. One of the most famous project in that field is the (Mussel Watch Programme ) but today they are used worldwide for that purpose (Ecotoxicology). * Tubifex worms: indicate nonpotable, stagnant, oxygen-poor water * Agave lechuguilla: an important indicator species in the Chihuahuan Desert 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Indicator species」の詳細全文を読む スポンサード リンク
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