The Five Levels of the Ecological System

On a Small Scale

• The smallest level of organization that the subject of ecology looks at is an individual living being, or organism. Although it is the lowest level ecology explores, the size of an individual organism can vary greatly, ranging from a tiny, single-celled organism to a much larger elephant or blue whale.

A Group of Organisms

• Above the individual, the next level of ecological organization is a population. A population includes all of the organisms of one given species that exist within a certain geographic area.

The Broader Community

• The level of biotic organization immediately above population is community. A community encompasses the populations of different species that live in a particular area and potentially interact.

Incorporate Nonliving Factors

• The ecosystem level of ecological organization includes the community of different species potentially interacting with each other. It also incorporates abiotic, or nonliving, factors in the specific area and the interactions between biotic, or living, and abiotic factors.

The Whole World Over

• The largest level of organization in ecology is the biosphere. The biosphere is the portion of the entire planet where life is found, including air, water and soil. Sometimes, an additional level of organization is included between the ecosystem and biosphere levels. Biomes are major communities in the world that are classified by the predominant vegetation type present and characterized by the adaptations of organisms in the environment. Examples of biomes include tundra and desert biomes.

Diagramming Energy Flow

• An ecosystem is sometimes divided into levels known as trophic levels, usually illustrated by a four- or five-tiered pyramid. The largest, lowest level of the pyramid contains the producers, or green plants, that use photosynthesis to transform sunlight into carbohydrates. The next level above producers consists of first-level consumers, or herbivores, that feed on producers. Above the first level of consumers are second-level consumers, which eat first-level consumers. Second-level consumers are in turn consumed by third-level consumers. Some of these upper-level consumers, like humans, may also feed on producers. Decomposers, which break down dead tissue, also play an important part in an ecosystem.