What is an Ecological Indicator?

What is an Ecological Indicator?


How does a plant or animal fit within an ecosystem? If one plant or animal becomes extinct or ceases to exist in an ecosystem what is the impact? Ecological indicators are species present in an environment that tell how healthy an ecosystem is. Indicator species can effectively survey a whole environment based on their presence or lack thereof. To understand nature figuring out the interdependence of species can take us a lot way as humans.

The wolves of Yellowstone are a prime example of how one species can have a major impact on the environment. Before settlers came to Montana and completely wiped out the wolves their job was to keep the elk and forests, river bottoms, and plant life healthy. Wolves prey of choice is elk. Without a species keeping the elk in check elk, numbers grew and grew. Bears and cougars are less effective predators of elk. This allowed the elk to roam freely in open ground where traditionally they were more vulnerable. Rivers turned into mud pits, plant life was affected, aspen trees stopped growing, and a whole generation of frogs, fish, dragonflies and more were destroyed because the elk had no threats in the valleys. When wolves were reintroduced to the ecosystem in the 1990’s the elk immediately changed their patterns. Those who did not were eaten.

Large carnivores effect prey species numbers. When wolves eat elk they can be pushed off a kill by a grizzly bear or wolverine. Typically, wolves are not pushed off their kill by a cougar or black bear. Wolves eating elk directly benefits species like ravens, bald eagles, golden eagles, foxes, coyotes, and other meat eating animals. Lynx have adapted to hunt their favorite prey the snowshoe hare. Lynx have evolved to move like snowshoe hares. When lynx or other large predators are not present in the ecosystem problems like disease and habitat destruction happen. When no hares are present in an ecosystem you can bet there are no lynx.

Great Grey Owls are an indicator species for old growth forests. The way humans manage forests directly impacts their numbers. Great grey owls prefer to breed in old growth forests they are an ecological indicator for healthy old growth forests. They prefer to nest in large trees in nests other birds have prey have built. They are nest stealers. Man made nests have been constructed but numbers are greater where old growth forests are present. Great grey owls are not aggressive like other large predators. They do not protect their territory. Most owls make calls throughout the night and call back to other owls of the same species. This is done to let other owls know their territory. Great grey owls do not do this which makes it more difficult to locate them in the field. Great grey owls do not scare easily and will often sit perfectly still using their natural camouflage if a human is nearby. Yew Trees are an ecological indicator of old growth forests. Yew trees prefer to grow in the shade and grow very slowly. When an old growth forest is logged all the yew trees are logged as well. Clear cutting techniques are not a healthy way to log forests.









Some indicator species: Click here for an Indicator Species Journal






Great grey owl

Rocky mountain tailed frog

Columbia spotted frog

Coeur d’Alene Salamander

Northern Alligator Lizard

Painted Turtle

Field Cricket

Flathead Minnow

Western Cutthroat Trout

Mountain Whitefish

Rocky Mountain Sculpin

Pacific Yew

Black Cottonwood