Understanding:
• An indicator species is an organism used to assess a specific environmental condition
Indicators species are sensitive to specific environmental conditions and consequently have a limited range of tolerance
- Their population growth or reduction indicates changes in the environment, making them a useful means of monitoring change
Indicator species may be sensitive to a number of different environmental conditions:
- Lichen, along with mosses, are susceptible to air-borne pollutants dissolved in water (e.g. sulfur dioxide)
- Tubifex worms are sensitive to concentrations of heavy metals
- Mayfly larva and certain aquatic invertebrates are sensitive to dissolved oxygen levels in water
Indicator Species
Understanding:
• Relative numbers of an indicator species can be used to calculate the value of a biotic index
Biotic indices compare the relative frequency of indicator species and provide an overall assessment of environmental health
- Calculating a biotic index involves multiplying the population size of each indicator species by its pollution tolerance rating
The following conclusions can be drawn from a biotic index:
- A high biotic index indicates the presence of many pollution-sensitive organisms, denoting an unpolluted environment
- A low biotic index indicates a polluted environment, due to a relative abundance of pollution-tolerant organisms
- A change in the biotic index over time marks a change in the environmental conditions within a given ecosystem
Pollution Tolerance and Environmental Pollution Levels
Practice Question
