Ecosystem Equilibrium: Definition & Example

Instructor: Amanda Robb
In this lesson we'll be learning about what equilibrium in ecosystems looks like. We'll explain the importance of equilibrium and look at examples of different ecosystems in and out of equilibrium.

What Is Ecosystem Equilibrium?

Imagine walking across a balance beam. You keep your arms out and sway from side to side as you walk across the beam. As long as you keep your weight in the center you stay balanced and stay on the beam. But if you become out of balance you fall off. Being in balance is important for many aspects of living things, not just playing on the playground.

All living things must remain in balance, or equilibrium, also known as homeostasis. Our bodies maintain a balance of many things such as temperature. If we are too hot we sweat and if we are too cold we shiver. Our temperature must remain in equilibrium.

Even larger collections of living things like ecosystems must be in balance too. An ecosystem is a collection of living and non-living things in an area. There are lots of types of ecosystems we already know, such as a forest or a meadow. Any collection of living and non-living things in an area is an ecosystem, even a small ecosystem like your backyard.

Importance of Equilibrium

Ecosystems must have just the right amount of non-living things like sunlight and water. But, they also need to have the correct balance of different species to stay in equilibrium. Too many or too few of a species can cause a population crash, where species in an ecosystem die off. Population crashes are devastating for ecosystems.

So how do ecosystems remain in equilibrium? Each ecosystem has a delicate food web that starts with producers, or organisms that make their own food. Plants, algae and phytoplankton are common examples of producers. This is the largest collection of organisms in an ecosystem. Think about how many individual blades of grass, trees, shrubs and other plants you see while hiking.

Primary consumers eat producers. These are animals like deer, squirrels, and rabbits. You might see a few of these on your hike through the woods, but you definitely see more producers. This is because there needs to be more producers than consumers in order to support their population. If there are too many consumers, they will eat all the food and the ecosystem will collapse.

Secondary consumers eat primary consumers. These animals include snakes, lizards, and small predators like foxes. There are even less secondary consumers than primary consumers. Again, you're even less likely to see these animals on a hike.

The last group of organisms in an ecosystem are called tertiary consumers. These animals eat both primary and secondary consumers. There are very few of them because there is less energy available at the top of the food web. If you're lucky in the forest you might see a wolf, eagle, or cougar as examples of tertiary consumers.

These patterns for populations of organisms apply to all ecosystems. There should be the most number of producers and the least number of tertiary consumers. Too many or too few of any level of the food web can have catastrophic effects.

Greater Yellowstone Ecosystem

In the 1800's wolves were habitually hunted in the greater Yellowstone ecosystem. By 1926 all of the wolves were killed off in Yellowstone park. Wolves were considered a danger to humans and a threat to livestock farming. But, wolves are a top predator in the Greater Yellowstone ecosystem. The hunting threw the entire ecosystem out of balance. Species such as this that regulate equilibrium are called keystone species.

Populations of primary consumers that were prey for the wolves increased, such as deer and elk. In order to feed themselves, they extended their diet from grass to other plants like willows. The loss of these trees ended up affecting other populations such as beavers. As the beavers decreased so did their dams, which changed the entire river landscape in Yellowstone. The reshaped rivers changed populations of fish and the animals that feed on them.

But in the 1990's scientists reintroduced wolves into the Yellowstone ecosystem. The effects were more drastic then scientists could have predicted. Surprisingly, the elk population stayed high, but the pressure from wolf predation kept the elk on the move which allowed the restoration of willow trees. This in turn allowed the beaver population to expand, changing the waterways of Yellowstone. Fish populations recovered as did their predators. The ecosystem returned to equilibrium with the reintroduction of this keystone species.

A pack of wolves chases an elk in the greater Yellowstone ecosystem
wolves and elk in Yellowstone

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