What are Indicator Species & Why Do They Matter?

What are indicator species & why do they matter?

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Every species on our planet has a unique role to play in maintaining the delicate balance of its ecosystem. Consider the apex predator, for instance. Its absence would trigger an upset in the food chain, resulting in a proliferation of prey species, which could have far-reaching consequences.

There are some creatures known as indicator species, and these play a vital role in monitoring environmental health. By detecting and tracking changes in their ecosystem, these species offer valuable information on the state of our planet.

What is an Indicator Species?

What is an indicator species?

A bioindicator species, or just, indicator species, is an organism that provides information on the condition of the local environment in any given area. Often, these are plant species or micro-organisms, but there are also several animal indicator species.

Indicator species can tell us a lot about the effects of pollution and climate change within an ecosystem. Researchers can look at the current population to get an idea of the health of the local environment and get clues as to how it is changing.

With pollution posing a significant risk to many plants and animals, indicator species can tell us a lot about its effects. The results of what researchers find can help them to make decisions on how best to support an ecosystem. This could be through the implementation of fishing rules, the use of chemicals, and replacing lost plants.

By monitoring indicator species, it reduces the need to look at several different species within an ecosystem. Not only would this be time-consuming, but it might also be impossible. But these bioindicators tell us everything we need to know about diseases, climate change, and pollution. What’s more, after addressing issues that are raised by looking at indicator species, we can continue to monitor them to track changes.

What Makes a Good Indicator Species?

The concept of an indicator species is that we can observe just one species within any given ecosystem to judge the condition of everything else that is found there. This saves time and confusion, but it’s no good just randomly picking a species to act as an indicator. In order to provide researchers with the most accurate information, an indicator species needs to have certain traits.

  • Some indicator species are found at the top of the trophic food chain which makes them the first in line to experience any toxins or changes in the environment; this allows researchers to pick up on things much more quickly.
  • Good indicator species will breed quickly and have a consistent diet and habits.
  • A good indicator species should be able to easily and rapidly adapt to change.
  • When choosing an indicator species, researchers will look for those that have a higher sensitivity to changes which again allows them to pick up on ecosystem degradation much more rapidly.
  • Researchers will also choose organisms that can be easily seen and observed.
  • The responses of a bioindicator should reflect those of the wider ecosystem.
  • Species chosen to be bioindicators should be common and well-studied.
  • When looking for an ideal indicator species, scientists will choose those that have unique biological and ecological traits.
  • When these creatures respond to changes, it should be done in a predictable manner. If they were to respond in an erratic manner, this might not serve as a warning that researchers can understand.

Examples of Indicator Species

There are many different types of bioindicators, from birds and mammals to plants and insects. Here, I’ll introduce you to some of the most important indicator species on the planet.


One of the main reasons lichens are chosen as a bioindicator is that different lichen species are sensitive to different things.

There are more than 18,000 species of lichens, and they’re found all over the world. These amazing organisms are a combination of fungus that creates their structure and algae which performs photosynthesis. As far as being important in an ecosystem is concerned, lichens are up there at the top.

They not only provide food, habitat, and shelter for animals but they’re also an essential indicator species.

One of the main reasons that they are chosen as a bioindicator is that different lichen species are sensitive to different things. There are some that thrive in nitrogen-rich environments, while others are much more sensitive to nutrients in the environment. This allows researchers to look at any given lichen species within any given area and determine things like air quality and the level of pollution.

Nitrogen is present in the atmosphere and most of the time, we breathe it in with no harmful effects. However, when it combines with oxygen, it creates nitrogen oxide which can be detrimental to human health. By studying lichens, we are able to act upon air quality changes much more quickly.

One of the other things that lichens are particularly sensitive to is sulfur dioxide and this can hinder their growth, so when scientists see that lichen is struggling in a particular location, this could indicate higher levels of the aforementioned chemical.

What’s great about using lichens as an indicator species is that they are not able to naturally defend themselves from environmental changes. They act as something of a sponge so it gives a very clear and rapid picture of what changes are occurring. Where there are very high levels of sulfur dioxide, there may be no lichens present at all.


Owing to this unique behavior, the mayfly serves as an excellent bioindicator.

Mayflies are very interesting creatures in the fact that, as adults, they will gather in huge swarms to breed before dying. However, these flies are very particular about the bodies of water that they’ll breed in which need to be free from pollution.

Owing to this unique behavior, the mayfly serves as an excellent bioindicator as was demonstrated in early studies back in the 1960s. At Lake Erie, where mayfly populations had once been abundant, pollution lowered the water quality causing the mayfly nymphs to die prematurely.

Since then, and particularly in the last quarter of a century, the mayfly has been incredibly helpful in assessing water quality in line with the federal Clean Water Act. As such, many bodies of water have been successfully cleaned just by looking at the abundance of mayflies in the area and taking action where pollution is a suggested result of a lack of these insects.

Water pollution doesn’t just impact mayflies; the excessive accumulation of silt in lakes and ponds can also have a profound effect on these insects. Nymphs, in particular, are highly vulnerable to siltation.

River Otters

River otters are also considered to be good indicator species because of their sensitivity.

When most people think of an apex predator, they imagine a wolf, a tiger, or a great white shark. But did you know that river otters are also apex predators? This is one of the traits that makes them such excellent bioindicators.

Being at the top of the food chain means that river otters are exposed to toxins in the ecosystem much more quickly than anything else. When they eat lower organisms like fish and insects, these toxins are passed on and they actually become more intense the further up the food chain they go. This essentially means that scientists are able to see the effects of these toxins in river otters before any other creature within the ecosystem. This gives them a clear picture of the water quality within the area.

What’s more, river otters are semi-aquatic animals, so they provide an easy way for scientists to look at the health of both the aquatic environment and the surrounding habitats. Moreover, their range also means that they can serve as indicators for both marine and freshwater habitats.

River otters are also considered to be good indicator species because of their sensitivity. In order to thrive, they need water that is low in contaminants as well as a good amount of clean vegetation around the water for shelter and raising their young.

American Crows

American crows are incredibly important in detecting the West Nile virus to which they are particularly susceptible.

Crows are sometimes seen as a pest, and many people look for ways to keep them out of their gardens. However, while they might serve as a nuisance, they’re actually incredibly important in detecting the West Nile virus to which they are particularly susceptible. Once the disease infects a population, it’s unlikely that many individuals will survive. So, authorities ask the public to report sightings of dead crows, and where there is an unusual number, this could indicate the presence of the virus.

By being able to detect an outbreak of the virus as early as possible, this allows preventative and protective measures to be put into place. However, it is worth noting that, while the West Nile virus can be contracted by humans, it cannot be passed from crows to humans.

Northern Spotted Owl

Northern spotted owls are used as an indicator species because their population levels can tell researchers a lot about the health of old-growth forests.

The northern spotted owl is another avian species that serves as an excellent bioindicator. In the 1990s, habitat degradation meant that this species was listed as endangered and since then, various conservation projects have been monitoring the owls in order to get a better idea of the ecological condition of their breeding grounds.

Northern spotted owls are only found in the Pacific Northwest where they inhabit old-growth forests. This is the main reason they are used as an indicator species because the population levels can tell researchers a lot about the health of these forests.

They do this by looking at the location of nesting pairs. Where nesting pairs are located within close proximity of one another, this suggests a greater abundance of prey. However, when they’re spread further apart, scientists can tell that the number of available prey species is not as great.

While this is one of the most endangered species of owl in the world, owing to its role as a bioindicator, the northern spotted owl is also one of the most studied.

Red-Cockaded Woodpecker

Red-cockaded woodpeckers are used as an indicator species to determine the health of pine forests.

Birds make amazing bioindicators for many reasons, and where the red-cockaded woodpecker is concerned, it’s because they are imperative in the management of pine forests. But how does this work?

Well, the red-cockaded woodpecker was once listed as an endangered species, although it’s recently been down-listed to threatened. This could only have happened because conservationists were monitoring the species and its behavior and managing the forests to ensure its survival. And their efforts seem to be working.

So, now that these birds have come back from the brink, it’s possible for us to use them to determine the health of pine forests. Red-cockaded woodpeckers will only inhabit healthy yellow pine forests with lots of old growth. Where numbers of these birds are high, this provides feedback that forest management programs are indeed working.

Peregrine Falcon

Peregrine falcons are used as an indicator species because they can give us a clear picture about the health of the environment.

The peregrine falcon is an endangered bird of prey species, and in some areas, it has been missing from the skies for many years. However, in the 1970s, programs to reintroduce the species to the wild were started, and while their numbers still aren’t huge, there has been a significant increase.

Looking at how well these birds thrive can tell us a lot, and they’re used as an indicator species because they can give us a clear picture about the health of the environment, which is one of the reasons that conservationists are so keen to protect them.

One of the biggest potential problems is the presence of toxic chemicals within an ecosystem, but these are largely left unmonitored. Pesticides like DDT are not currently monitored in birds of prey, even though this chemical has been outlawed. But since the peregrine falcon and other raptors are at the top of the food change, the effects of any toxin would be immediately apparent.


Frogs have a special type of skin that water can penetrate through, this means that, if there are any toxins such as pesticides in the water.

There are currently around 5000 known species of frogs, and more are being discovered all the time. Since frogs live both in water, as tadpoles, and then on land when they’re adults, this makes them an excellent indicator species as they’re able to tell us a lot about the condition of both types of habitat.

One of the things that scientists look for when choosing an indicator species is its uniqueness and that could not be more true of frogs. These amphibians have a special type of skin that water can penetrate through. This means that, if there are any toxins such as pesticides in the water, the frogs will be one of the first creatures to react to this.

Moreover, since frogs prey on many smaller creatures such as flies, spiders, and other insects, they control these populations, which may otherwise be harmful to humans.

However, habitat loss and fragmentation is a serious problem for frogs, many of whom are under threat. There are several efforts in place to protect these important bioindicators to ensure they can continue helping us understand the health of the ecosystems in which they are found.

American Pika

The lack of pikas in any given location can tell researchers a lot about the current effects of climate changes and therefore make good indicator species.

Climate change is a very obvious problem that affects every living thing on this planet. There are some animals, like the American pika, that are adapted to survive in very specific conditions. In this case, the pika has a thick coat that allows it to endure the cold winter temperatures in the mountains, many thousands of feet above sea level.

In fact, these animals are so sensitive to temperature changes that if they are exposed to temperatures above 77ºF (25°C), they won’t survive. That’s bad news for the pika, but it does make them an interesting bioindicator that can tell us a lot about climate change.

These creatures don’t typically live at altitudes below 8,200 feet (2499 meters), but as global warming sets in, they’re being forced higher and higher. The lack of pikas in any given location can tell researchers a lot about the current effects of climate change. However, while continued climate change could threaten the very survival of these adorable creatures, there is evidence to suggest that they’re able to adapt their genes to cope at higher altitudes with less oxygen. 


Grunion is a toothless amphibious fish that primarily feeds on plankton.

The grunion is an interesting species of fish that comes to the shore to lay its eggs. However, it’s also an incredibly sensitive species that won’t reproduce successfully on beaches where there has been too much human interference or the conditions aren’t spot on.

So, this makes the grunion a very useful indicator species since researchers can assess the breeding success on any given beach to determine the health of the area.

There are lots of projects that look at the conditions of the beach compared to grunion reproductive success, and this also tells us much about the species. For example, it’s now thought that beach fill or shores that are too steep could be problematic for the species. In turn, humans can ensure as many natural, healthy environments as possible for these fish to breed.


As far as aquatic bioindicators go, the salmon is a brilliant example.

As far as aquatic bioindicators go, the salmon is a brilliant example. These fish are unique in that they travel between the ocean and freshwater for breeding. If they cannot move between the two locations then they will be unable to survive.

When the salmon begin behaving in a different way this can be a result of things like a decline in water quality and a degraded habitat which gives researchers an early indication that something is wrong. On top of that, salmon acts as a bioindicator for various diseases.

The problem for these fish is that without access to clean, cold waters, they won’t survive and while they are telling us about the condition of our waterways, it’s not necessarily good news. In fact, conditions are so bad in some places that as many as 85% of Atlantic salmon have been lost in the last quarter of a century. If things continue the way they are, there’s a risk that they’ll become extinct within the next 30 years.

The good news, however, is that because these fish act as bioindicators, conservationists can start to work on improving water quality to ensure the survival of the salmon.

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