Indicator Species: Definition & Examples

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

An indicator species can tell scientists a lot about a habitat. This lesson will define the term 'indicator species' and then outline some examples of creatures that can indicate healthy water, air, and forest.

What is an Indicator Species?

What if I were to tell you a species of owl can tell scientists the overall health of old growth forests in the Pacific Northwest? Yep, it's true! The spotted owl only inhabits old growth forests and scientists decided to start tracking their numbers in 1985. They found that the number of owls declined every year.

The spotted owl is an example of an indicator species, or an organism that shows the overall health of an environment. This could be an animal, like the owl, a bacterium, a plant, a fish, well you get the idea.

By studying the spotted owl, scientists can determine the relative abundance of other species such as the northern flying squirrels, Douglas firs, and truffle mushrooms, just to name a few. How does the owl tell us about those other species? Well, the owl eats flying squirrels, which eat truffle mushrooms. The truffles will only grow in shady, cool areas offered by the Douglas fir. Yep, everything is connected!

Spotted owl

Based on declining spotted owl numbers, it's safe to deduce that mature forests in the Pacific Northwest are not doing well. This is mainly due to deforestation as well as partial habitat loss as parts of the forest are cut and the habitat is fragmented. Let's check out some other indicator species.

The Worm Tubifex tubifex

Our next example is a worm called Tubifex tubifex. Tubifex worms live in the mud of streams and lakes. This worm allows scientists to determine the overall health of bodies of water because it is really tolerant to conditions that occur when there is pollution, such as low-oxygen levels or heavy metal contamination in the water. It will survive in areas where other critters cannot. When scientists find a lot of this worm, they know that the water quality is not good.

Tubifex worms


Another indicator species is lichen, which is actually made up of two species: alga and fungi, which live together in a symbiotic relationship (both species benefit from teaming together). Lichens are very sensitive to air pollution, specifically sulfur dioxide, which is a produced from burning fuels and can be emitted from power plants, vehicles, industrial buildings, etc.

When lichen absorbs sulfur dioxide, it messes up the alga's chlorophyll and prevents photosynthesis from occurring, killing the lichen. In regions with a lot of sulfur dioxide pollution, lichens will be sparse or absent, whereas when sulfur dioxide is not present, the more sensitive lichens will thrive.

Lichen are indicators of air quality


The last indicator species we'll check out are stoneflies, which live in the mud of freshwater when they are in their larval stage. There are actually tons of different species that fall under the generic name 'stonefly,' but many of those are good indicators of stream health.

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