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.
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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. 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 resuspension. 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
Definitions
Lindenmayer et al. suggest seven alternative definitions of indicator species:
- a species whose presence indicates the presence of a set of other species and whose absence indicates the lack of that entire set of species;
- a keystone species, which is a species whose addition to or loss from an ecosystem leads to major changes in abundance or occurrence of at least one other species
- a species whose presence indicates human-created abiotic conditions such as air or water pollution (often called a pollution indicator species)
- a dominant species that provides much of the biomass or number of individuals in an area
- a species that indicates particular environmental conditions such as certain soil or rock types
- a species thought to be sensitive to and therefore to serve as an early warning indicator of environmental changes such as global warming or modified fire regimes (sometimes called a bioindicator species)
- a management indicator species, which is a species that reflects the effects of a disturbance regime or the efficacy of efforts to mitigate disturbance effects.
Type 1, 2, and 4 have been proposed as indicators of biological diversity and types 3, 5, 6, and 7 as indicators of abiotic conditions and/or changes in ecological processes.