What is an ecosystem?
An ecosystem is all the living and nonliving things in an area, and all the ways they interact. An ecosystem can be as big as an ocean or as small as a puddle.
Living and nonliving parts
| Biotic factors (living) | Abiotic factors (nonliving) |
|---|---|
| Plants | Sunlight |
| Animals | Water |
| Fungi | Soil |
| Bacteria | Air |
| Temperature | |
| Rocks |
Biotic and abiotic factors affect each other. Plants need sunlight, water and soil. Animals need plants and water. Worms and fungi break down dead things, adding nutrients back to the soil.
Levels of organization
| Level | Meaning | Pond example |
|---|---|---|
| Organism | One living thing | One frog |
| Population | All of one species in an area | All the frogs in the pond |
| Community | All the populations in an area | Frogs, fish, ducks, cattails, algae |
| Ecosystem | The community plus abiotic factors | The community plus water, mud, sunlight |
Roles in an ecosystem
- Producers make their own food using sunlight. (Plants, algae)
- Consumers eat other living things. (Rabbits, hawks, people)
- Decomposers break down dead things and wastes. (Mushrooms, bacteria, worms)
Without decomposers, dead leaves and animals would pile up and nutrients would never return to the soil.
How living things interact
Predator and prey
A predator hunts and eats another animal, called the prey. Owls eat mice; wolves eat deer. When there are lots of prey, predator numbers often rise. When prey numbers fall, predators may go hungry and their numbers fall too.
Competition
Competition happens when living things need the same resources, such as food, water, sunlight or space. Two trees compete for sunlight. Squirrels and blue jays compete for acorns.
Symbiosis
Symbiosis is a close relationship between two different species.
| Type | Who benefits? | Example |
|---|---|---|
| Mutualism | Both benefit | Bees get nectar; flowers get pollinated |
| Commensalism | One benefits; the other isn’t affected | A bird nests in a tree |
| Parasitism | One benefits; the other is harmed | A tick feeds on a dog’s blood |
Changes in ecosystems
Ecosystems change. Some changes are natural, like floods, droughts, fires and seasons. Others are caused by people, like building roads, cutting forests and polluting water.
When one part changes, other parts are affected. If a disease kills many rabbits, foxes have less food. If people add a new species, it may out-compete the species already there.
Balance
A healthy ecosystem has many kinds of living things. This variety, called biodiversity, makes it stronger. If one food source disappears, animals can often eat something else.
In the real world
When wolves were brought back to Yellowstone National Park in 1995, they hunted elk. With fewer elk eating young trees by the rivers, willows grew back, and beavers returned. One change rippled through the whole ecosystem.
Common mistakes
- Forgetting abiotic factors. Sunlight, water and temperature are part of the ecosystem too.
- Thinking all symbiosis is helpful. Parasitism harms one partner.
Try it yourself
- Choose a park, schoolyard or backyard. List five biotic and five abiotic factors.
- Find one example of competition and one of symbiosis.
- Predict what would happen if all the bees disappeared from that ecosystem.
Quick recap
- An ecosystem is living and nonliving things interacting.
- Biotic factors are living; abiotic factors are nonliving.
- Producers, consumers and decomposers all have roles.
- Predation, competition and symbiosis are ways living things interact.
- A change to one part of an ecosystem affects the others.