Components of an Ecosystem

Every ecosystem, regardless of its size or type, is built from two broad categories of components that continuously interact with one another: abiotic components, which are the non-living physical and chemical features of the environment, and biotic components, which are the living organisms present.

The abiotic components can themselves be grouped into physical factors and chemical factors. Physical factors include sunlight (the primary energy source for almost every ecosystem on Earth), atmospheric or water temperature, precipitation and humidity, the physical structure and texture of the soil or sediment, and, in aquatic systems, additional factors such as water depth, current and light penetration. Chemical factors include the inorganic substances present in the environment -- carbon dioxide, oxygen, water, nitrogen, phosphorus and various mineral ions such as calcium, potassium and magnesium -- as well as the organic compounds, such as proteins, carbohydrates, lipids and humic substances in the soil, that link the non-living and living parts of the ecosystem together, since these organic molecules are ultimately produced by living organisms yet exist, for a time, as part of the surrounding dead organic matter and soil chemistry.

The biotic components are the living organisms of the ecosystem, and they are classified by the functional role each plays in the movement of energy and matter, not simply by taxonomic group. Producers, or autotrophs, are organisms able to manufacture their own organic food from simple inorganic raw materials, almost always by photosynthesis; on land these are chiefly green plants, and in water they are chiefly phytoplankton, algae and certain photosynthetic bacteria, with a much smaller contribution from chemosynthetic bacteria that derive energy from inorganic chemical reactions rather than sunlight. Producers form the base on which every other biotic component in the ecosystem ultimately depends, since they are the only organisms capable of converting the sun's radiant energy into a chemical form that other organisms can use as food.

Consumers, or heterotrophs, are organisms that cannot manufacture their own food and instead obtain organic nutrition by directly or indirectly depending on producers. They are further divided by what they feed on: herbivores (primary consumers) feed directly on producers -- a grasshopper eating grass, a deer browsing on leaves, or zooplankton grazing on phytoplankton; carnivores feed on other consumers, and are themselves sub-divided into secondary consumers, which feed on herbivores (a frog eating a grasshopper, a small fish eating zooplankton), and tertiary consumers, which feed on secondary consumers (a snake eating a frog, a large fish eating a small fish); and omnivores, such as crows, bears and humans, feed on both plant and animal matter, occupying more than one trophic role depending on what they eat at a given time. …