What Is an Ecosystem?

What Is an Ecosystem?

An ecosystem is a community of all the living things in an area - along with all the nonliving things - working together as a system. The word comes from eco (home) and system (a set of interacting parts).

Ecosystems come in every size: a puddle, a forest, a coral reef, the entire Amazon rainforest, or even a rotting log. What makes something an ecosystem is not its size, but that its living and nonliving components interact and depend on each other.

Biotic and Abiotic Factors

Every ecosystem has two types of components:

Biotic (living): All organisms in the ecosystem - Trees, deer, bacteria, fungi, birds

Abiotic (nonliving): Physical and chemical environment - Sunlight, temperature, water, soil, air Changes in abiotic factors directly affect biotic factors. A drought (abiotic) reduces plant growth (biotic), which reduces food for herbivores, which reduces prey for carnivores - a cascade through the whole ecosystem.

Roles in the Ecosystem

Producers

Producers (mostly plants and algae) use sunlight to make their own food through photosynthesis. They form the base of every food chain and are the primary source of energy in the ecosystem.

Consumers

Consumers cannot make their own food - they eat other organisms.

• Primary consumers (herbivores): eat plants - rabbits, deer, caterpillars

• Secondary consumers: eat primary consumers - frogs, small fish, foxes

• Tertiary consumers / apex predators: top of the food chain - eagles, sharks, lions

Decomposers

Decomposers break down dead plants and animals, returning nutrients to the soil. Without decomposers, dead matter would pile up and ecosystems would run out of nutrients.

Examples: mushrooms, bacteria, earthworms, beetles

Food Chains vs. Food Webs

A food chain shows a single straight path of energy. A food web shows all the interconnected feeding relationships in an ecosystem - which is much closer to reality, because most animals eat more than one thing and are eaten by more than one predator.

Energy Flow in Ecosystems

Energy enters an ecosystem through producers capturing sunlight. At each level of the food chain, about 90% of energy is lost as heat - only 10% passes to the next level. This is why ecosystems support far more plant mass than animal mass, and more herbivores than carnivores.

Types of Ecosystems

• Terrestrial: forest, grassland, desert, tundra

• Freshwater: ponds, rivers, lakes, wetlands

• Marine: coral reefs, open ocean, kelp forests, estuaries

Ecosystem Health and Threats

A healthy ecosystem has biodiversity - many different species filling many different roles. Threats to ecosystems include:

• Habitat destruction (deforestation, development)
• Pollution (air, water, soil)
• Invasive species (non-native organisms that outcompete native ones)
• Climate change (shifts in temperature and precipitation patterns)

Practice Activities

• Build a food web: Give students organism cards from a local ecosystem and have them draw arrows showing who eats whom.

• Biotic vs. abiotic sort: Students sort pictures of ecosystem components into living and nonliving categories.

• Ecosystem diorama: In groups, students build a 3D model of a specific ecosystem with labeled organisms and abiotic factors.

• Ecosystem collapse simulation: Remove one organism from a classroom food web (on paper) and trace the effects through the ecosystem.

• Backyard ecosystem survey: Students record every living and nonliving thing they can observe in a small outdoor area.

---