Indicator Species: Using Frogs and Salamanders to Gauge Ecosystem Health

Use amphibians, like salamanders, toads and tree frogs, and other indicator species to show when pollutants threaten local ecosystem health.

| July/August 2013

  • Indicator-Species
    Three bull frogs resting on rocks in a pond.
    Photo By iStockphoto/Benjamin Loo
  • Red-Backed-Salamander
    The southern red-backed salamander (Plethodon serratus) captured in Cobb County, Georgia.
    Photo By Allen Blake Sheldon
  • Spotted-Salamander
    A spotted salamander (Ambystoma maculatum) in Monroe County, Tennessee.
    Photo By Allen Blake Sheldon
  • Marbled-Salamander
    The colorful marbled salamander (Ambystoma opacum).
    Photo By Allen Blake Sheldon
  • Small-Frog
    A small frog surveys its surroundings.
    Photo By iStockphoto/craigdamlo
  • Salamander-Eggs
    Salamander eggs are usually seen in the spring.
    Photo By iStockphoto/Mark Kostich

  • Indicator-Species
  • Red-Backed-Salamander
  • Spotted-Salamander
  • Marbled-Salamander
  • Small-Frog
  • Salamander-Eggs

Ecologists and environmental scientists use a wide range of plants and animals as “indicator species” to get an idea about ecosystem health of streams and forests. Some of these species are tolerant of pollution — such as certain bacteria or algae — so their presence indicates the presence of pollutants like sewage. Other species are intolerant of pollution or environmental disturbance — such as mayflies or many fish species — so their presence is an indicator of a healthy ecosystem, while their absence can indicate problems. One group of organisms most sensitive to environmental change appears to be amphibians, which includes frogs, toads and salamanders.

For many years, scientists have been noticing a severe decline in amphibians around the world. Many species have completely disappeared, while others have become extremely rare or have started developing deformities — like extra legs. As a result, amphibians have come to the forefront as indicator species. But you don’t have to be a professional ecologist or environmental scientist to help monitor this decline. You can do something as simple as keep an eye on your garden.

Why is the amphibian population so sensitive?

One thing that makes frogs, toads and salamanders such sensitive environmental indicators is their skin. Unlike reptiles, birds and mammals, amphibians are still partially tied to the water, spending at least part of their life cycle as eggs and juveniles in an aquatic environment. The eggs don’t have a hard shell around them like the eggs of reptiles and birds, and must remain in the water, or they will dry out. The juvenile forms, or tadpoles, breathe through gills like fish, extracting oxygen from the water. Not until they develop into adults do amphibians possess lungs (well, most of them anyway), allowing them to leave the water.

Even as adults, most amphibians have to keep their skin moist by staying near water or damp areas, since they breathe partially or entirely through their skin. (There are a few species of salamanders called “lungless salamanders” because they have no lungs and depend completely on their skin to breathe.) Because their skin is so porous and absorbs gases, like oxygen, and liquids, like water, amphibians at all stages of life are sensitive to environmental changes, especially many types of pollution that may be in the atmosphere, water or soil.



What does all this have to do with the health of your garden? Whatever affects amphibians also may affect people. Because frogs, toads and salamanders are so sensitive to pollutants, and because they are so much smaller than humans, they will likely show signs of problems in your garden before it affects you. They can serve the same function that canaries used to serve for coal miners years ago: Being more sensitive to poisonous gases than the humans, when the canary became sick or died, the miners knew something was wrong.

If you provide abundant habitat for amphibians and have a healthy population of them in and around your garden, that is a good indicator that you have a healthy environment. If they start disappearing or showing deformities, you might have some problems, especially with your water or soil.

RobertBulger
8/8/2018 8:49:08 AM

Can amphibians be used to indicate water quality for small decorative ponds that may only be seasonally used in areas like the midwest that winters typically cause a shut down of the pond?


BethannyParker
11/3/2014 9:42:38 PM

How do you build habitat for desirable amphibian species without also attracting bullfrogs, which could devastate the amphibian populations you already have?




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