Nature's four realms – land, ocean, freshwater and atmosphere – include different types of ecosystem or 'biome', such as tropical forests, and rivers and streams.

The biome concept organizes large-scale ecological variation. Terrestrial biomes are distinguished primarily by their predominant vegetation, and are mainly determined by temperature and rainfall. Differences in temperature or precipitation determine the types of plants that grow in a given area (Figure 1).

A biome is an area classified according to the species that live in that location. Temperature range, soil type, and the amount of light and water are unique to a particular place and form the niches for specific species allowing scientists to define the biome.