What are indicator species? Understanding nature’s detectives
When ecologists examine our natural world, they look at certain species, which can help them understand how healthy and abundant their ecosystem is. These are known as indicator species, and they provide scientists and conservationists with crucial information about the state of an ecosystem, and the processes within it.
These natural bioindicators are often examined to help conservationists monitor environmental changes and predict ecological shifts, which can help them be more proactive in protecting ecosystems from biodiversity loss and climate damage. In this article we will take a deep dive into indicator species, how they’re identified, and what examples you could look out for in your own backyard.
What are indicator species?
Understanding and monitoring ecosystem health is crucial to biodiversity conservation, and indicator species are nature’s way of letting us know when it’s in trouble. For a more scientific explanation, indicator species are a species, or group of species, that reflect the biotic* or abiotic* state of an environment. They reveal the possible evidence and impact of environmental change, and indicate the diversity of other species, taxa*, or entire communities within an area.
When an indicator species vanishes from an ecosystem, or its population moves or changes, it’s a sign that something is wrong. It could indicate a change in water or air quality, or the impact of a warming environment or the presence of pathogens (microorganisms, viruses, toxins, etc) and disease. When these changes occur, indicator species are the first to respond, either by leaving an ecosystem or by perishing. These changes alert conservationists to instability in the environment. Some indicator species are also keystone species.
How are indicator species identified?
Bioindicators tend to be identified based on research into a specific population, local abundance, and ecological significance and/or conservation status, or a combination of two or more of these reasons. Indicator species respond quickly to environmental changes, which means they are usually the first to be affected by rising temperatures, pollution levels, or changes in habitats. When scientists look into what makes an animal or organism an indicator species, they look for a population with large enough numbers and across a large enough area so that it’s easy to research. They should also reproduce quickly so that conservationists can assess whether their interventions are working or if they need to try a different approach to their efforts.
Indicators species examples
Around 50% of indicator species are animals, and 70% are invertebrates! These are creatures without a backbone such as starfish, earthworms, jellyfish, spiders, snails, etc. An indicator species can be any organism that is abundant and sensitive to changes in the environment. Here are several examples of bioindicators that help alert conservationists to our changing natural world.
Amphibians
Amphibians like frogs, toads, and salamanders are particularly sensitive to environmental conditions and can't easily migrate to healthier ecosystems. They are also found all over the world in a number of different ecosystems and habitats, which is why it’s particularly troubling that 41% of amphibians are globally threatened with extinction. The disappearance of amphibians can indicate poor water quality or habitat degradation from human-induced factors such as deforestation, cultivation, grazing, and mowing.
Benthic macroinvertebrates
Fly larvae, worms, and small crustaceans are all examples of what scientists call benthic macroinvertebrates. These tiny, spineless aquatic organisms can be seen with the human eye and help conservationists monitor water quality. This is done by tracking any changes in the number of individual species.
Benthic macroinvertebrates can be found everywhere except the worst polluted lakes, rivers, and aquatic habitats. This is because they are tolerant to many types of pollution. When there is more diversity of these creatures in a stream, for example, it can indicate good water quality. If the same stream contains only pollution-tolerant macroinvertebrates, it tells scientists that something is wrong. Their presence (or absence) can also signal environmental factors other than pollution, such a change in water currents or drought.
Monarch butterflies
This strikingly beautiful and iconic butterfly has immense ecological value. Adult Monarch butterflies only live for around three to four weeks, and are particularly sensitive to environmental changes. Their short lifespan means that changes within and between the generations are more pronounced and can be monitored easily by ecologists. They also have an enormous range across the United States, migrating between northern America in summer to Mexico and California in winter. Unfortunately, Monarch butterfly populations have plummeted by 90% since the 1990s, which gives us a sobering picture of the ongoing impacts of climate change.
Lichens
Lichens are complex organisms. They can usually be found on leafy trees or exposed rock. They are very important for filtering and trapping particulate matter from the air, and play a key role in creating cleaner, healthier air for us to breathe. They are particularly sensitive to nitrogen pollution, and when air quality is bad, lichens are some of the first to suffer. Scientists can monitor the amount of chlorophyll* in lichen, and if it decreases, then we know that air pollution is present.
Owls
Certain species of owl—like the northern spotted owl or little owl—are indicator species. Northern spotted owls rely on the tree cavities and broken treetops of old-growth forests for nesting and hunting. They tend to expand their territory when less prey exists, and their population size decreases when fewer nesting sites are available. Conservationists can monitor northern spotted owls in forest habitats to determine pressure from developments, logging, and disease. In 1990, they were listed as a threatened species due to habitat loss.
Little owls are another owl species that has been identified as an indicator. When these owls are present, it’s a sign that their ecosystem is healthy enough to support their nests and food supply. This is why the Planet Wild team returned to rural Germany to give these owls a fighting chance of returning to this part of the country.
Salmon
Salmon are anadromous fish, which means they need uninterrupted river systems to travel between their freshwater breeding grounds and the open ocean—a process crucial to their survival. Overfishing, river damming, and habitat destruction has led to a significant decrease in salmon populations around the world. Bears and other predators also rely heavily on salmon migration for food through the harsh winter months.
Salmon are sensitive to pollutants, habitat disruptions, and changing temperatures, so their decline from an area provides vital insights into damaged ecosystems.
Coral
It’s easy to see why coral reefs are such good indicators of aquatic health. When a coral reef is healthy, millions of species teem around the colorful structures. Coral reef ecosystems are some of the most beautiful on Earth, but sadly the vital life-giving corals are incredibly sensitive to temperature changes, pollution, and ocean acidification.
Corals are made up of thousands of polyps, which secrete calcium carbonate to protect them, forming those impressive colorful structures. When ocean temperatures rise, coral is the first to react. When under stress, the corals expel algae that lives in their tissues. This causes them to lose their color and appear transparent, revealing its white skeleton. Bleached coral isn’t dead, but it’s much more susceptible to disease and starvation. This matters because when reefs die, they struggle to come back. Coral bleaching signals to ocean conservationists that a reef is in trouble.
Indicator species can be thought of as nature’s way of pointing out a problem before it gets out of hand. This is why it’s so important to identify, monitor, and act when these species begin to show signs of decline and deterioration. Long-term monitoring can also give key data on trends that could show larger environmental changes over time.
*Glossary of Terms
Abiotic: Physical rather than biological. Examples include sunlight, air, precipitation, minerals, and soil.
Biotic: Biological, relating to or resulting from living organisms.
Chlorophyll: The natural compound present in green plants which gives them their color. It is a key compound that helps plants to absorb energy from the sun.
Taxa: A scientifically classified group or entity.
Sources
'Indicator Species', Science Direct
'What Is an Indicator Species? 10 Key Examples', TreeHugger, 2022
