1.1 Introduction to Ecosystems

What defines an ecosystem?

An ecosystem is a community of living organisms (biotic factors) interacting with their nonliving environment (abiotic factors) like sunlight, water, temperature, and soil. Ecosystems can range from small ponds to entire biomes. Energy and matter flow through ecosystems, connecting organisms via feeding relationships and nutrient cycles.

Ecosystem diversity is driven by climate

Latitude, elevation, and seasonality shape climate patterns, which determine what type of ecosystem forms in a region. Areas near the equator receive intense, consistent sunlight, creating warm, stable climates (like tropical rainforests), while higher latitudes experience more seasonal variation, leading to biomes like tundra or temperate forest.

Energy flow and the sun

Nearly all ecosystems are powered by the sun, whose energy is captured by producers (autotrophs) through photosynthesis. This energy then flows through food chains and food webs to consumers. Because energy is lost as heat at each transfer, ecosystems require a continuous input of solar energy to sustain life.

Key terms

Ecosystem

A community of living organisms interacting with each other and their nonliving environment.

Biotic factors

The living components of an ecosystem, such as plants, animals, and microbes.

Abiotic factors

The nonliving components of an ecosystem, like sunlight, temperature, water, and soil.

Producers (autotrophs)

Organisms that convert solar energy into chemical energy via photosynthesis, forming the base of food webs.

Why energy input must be continuous

Energy is lost as heat at each trophic transfer, so ecosystems rely on constant solar energy input to sustain life.

Try an AP-style question

Clownfish live among sea anemone tentacles, gaining protection while cleaning the anemone. What relationship is this?

1. Commensalism
2. Mutualism
3. Competition
4. Parasitism