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Why ‘indicator’ species matter

Project #D – PLANETARY LIMITS: Climate change, Biodiversity Loss

By Alex Gow-Smith and Jane Fiona Cumming

Whilst most companies are now measuring their performance and setting targets relating to climate change impacts, very few are doing the same for biodiversity loss. The alarming rate of species loss is well documented, but this blog focuses on indicator species, those that serve as nature’s own early warning systems for climate change and pollution.

Indicator species are a crucial aspect of nature that offer, through understanding of environments, a way to measure biodiversity loss and act accordingly. An indicator species, also known as a bioindicator, is an organism that reflects the condition of the environment around it. They’re often the first in their ecosystem to be affected by a particular environmental change, such as a warming climate or pollution. By monitoring changes in the behaviour, physiology, or population of an indicator species, scientists can monitor the health of its whole environment.

The following characteristics are necessary for an effective indicator species:

· Its health should be a bellwether for the health of other species in the same ecosystem

· Any changes it undergoes should be clear and measurable

· It should respond to change in a predictable way.

Examples of indicator species:

Northern Spotted Owls are a widely studied indicator species. Scientists observe them to get a sense of the overall health of old-growth forest ecosystems and to monitor the effects of human-caused habitat changes. Native to the Pacific Northwest, the owls make their nests in old tree cavities, broken treetops, and abandoned raptor nests, all found in the region’s old-growth forests. However, as forests have been cleared for logging, agriculture, and urban development, the owls have lost their nesting sites, causing their populations to plummet, with a continued decline of 4% each year making Northern Spotted Owls officially a threatened species. Their decline signals that other species in the forest are likely declining as well and that the forest—and the web of life that sustains it—has been degraded. Similarly, a population of thriving Northern Spotted Owls indicates that an ecosystem is healthy and able to support an array of other plants and animals.[1]

Northern Spotted Owls

Lichens, a complex life form that is a partnership of two separate organisms - a fungus and an alga, act as indicators for air pollution levels (in particular, sulphur dioxide). They grow in exposed places such as rocks or bark. Due to the harsh environments in which they live, lichens must be very efficient at absorbing water and nutrients, with rainwater containing just enough nutrients to keep them alive. Air pollutants dissolved in rainwater can prevent them from growing, thus making lichens natural indicators of air pollution.

For example:

  • Fruticose (bushy) lichens need very clean air.

  • Foliose (leafy) lichens can survive small amounts of air pollution.

  • Crustose (crusty) lichens can survive in more polluted air. [2]


Pikas—small, furry mammals—are perfectly adapted to living in harsh high-alpine habitats, which means that even the smallest changes to their environment affect them. Instead of hibernating to get through the winter, pikas take cover under rocky debris, relying on the insulation of heavy winter snowpack to keep their dens warm. In the 2000s, researchers noticed declines in pika populations at lower elevations, especially in the driest parts of the western USA. This showed the impact of global warming.


Water pollution is caused by the discharge of harmful substances such as untreated sewage into rivers, lakes, and seas. Many aquatic invertebrate animals cannot survive in heavily polluted water (from discharge of harmful substances, such as untreated sewage)- this is mainly due to the resulting lowering of the oxygen concentration. These animal’s presence (or absence) indicates the extent to which a body of water is polluted. POLLUTION

Level of Water Pollution

Example Indicator Species


Stonefly nymph, Mayfly lava


Freshwater shrimp, Caddis fly lava


Bloodworm, water louse


Sludgeworm, Red-tailed maggot

Very High

No living insects

Stonefly nymph Freshwater shrimp

Indicator species and keystone species

A term first coined by Robert Paine in 1969, keystone species are those that have a disproportionately large effect on their environments.[3] This is because they are no other species in the ecosystem that can serve their same function. Without them, the ecosystem would change dramatically or could even cease to exist. Therefore, efforts must be made to understand which animals are keystone species and ensure that they are protected. For example, beavers are a keystone species. They build dams that create wetland habitats in which many other species thrive.

While keystone species are vital to sustaining their ecosystem, they may or may not be uniquely susceptible to environmental change—a key characteristic of indicator species. Some species, however, are both.

The white ash tree may be considered an indicator species; hundreds of millions of ash trees have been killed by the invasive emerald ash borer. But white ash trees are also keystone species. They provide food and habitat to dozens of animal species and act as a sink for air pollutants. [4]

White Ash Tree

Why are indicator species important?

By studying indicator species, scientists can keep a finger on the pulse of an entire ecosystem’s health without having to spread monitoring resources across multiple species and locations. Indicator species can reveal indirect biotic effects of pollutants when many physical or chemical measurements cannot. Indicator species can be also used a management tool for investigating the status of an environmental condition, find a disease outbreak, or monitor climate change, within a particular ecosystem. They could be regarded as an “early warning system” for that area. However, indicator species related analysis must also be accompanied by a thorough study of what is being indicated, what is really correlated, and how this one species fits into the rest of ecosystem.

ARTICLE 13 VIEWPOINT - What does this mean?

Our latest practitioner research shows only 7% of the world’s largest companies reviewed are setting a target for biodiversity loss. Of that handful of targets set, none were at scale with what the planet needs. See a snapshot of our latest research here.

Businesses must firstly commit to measuring their full impact on the planet’s resources – not just carbon reduction - and base reduction targets on what the world needs them to do. Secondly, businesses can help support biodiversity conservation and restoration programmes related to their supply chains, areas of operation and markets that they serve.

Article 13 is an SBTN Corporate Engagement Program participant, pledging alignment with SBTN’s goals and vision and contributing advice and end-user insights to the development of SBTN methods and tools. If you would like to know how Article 13 can support you to measure your impact on Planetary Limits and Social Thresholds, get in touch.



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