Terrestrial biomes

Ecosystems (Form and function) · Adaptation to environment · note 4 of 5

Spec B4.1.6, B4.1.7Download all Adaptation to environment notes (PDF)Download all notes (PDF)9 pages

Terrestrial biomesSpec B4.1.6, B4.1.7

In short

A biome is a group of ecosystems with similar communities due to similar abiotic conditions and convergent evolution. Temperature and rainfall are the abiotic factors that determine terrestrial biome distribution: for any given pattern of the two, one natural ecosystem type is likely to develop, such as tropical forest where it is hot and wet all year.

Abiotic factors are the determinants of terrestrial biome distribution. The two most important are temperature and rainfall. For any given temperature and rainfall pattern, one natural ecosystem type is likely to develop.

Graph of mean annual precipitation (0 to 4000 mm) against mean annual temperature (−15 to 30 °C) with regions for tundra (cold, dry), taiga (cold, low to moderate rainfall), temperate forest (moderate temperature and rainfall), grassland (moderate to hot, low to moderate rainfall), hot desert (hot, under 250 mm) and tropical forest (hot, very high rainfall). — Temperature and rainfall together decide which biome develops. Boundaries are approximate and illustrative.

A biome is a group of ecosystems with similar communities due to similar abiotic conditions and convergent evolution. Unrelated species in different continents face the same selection pressures, so they evolve similar adaptations. For example, cacti in American deserts and spurges (Euphorbia) in African deserts are not closely related, yet both have water-storing green stems, spines and reduced leaves.

Climate conditions of six terrestrial biomes
Biome	Temperature	Rainfall
Tropical forest	High all year (monthly means about 25–27 °C), little seasonal change	Very high (often over 2000 mm per year), spread through the year
Temperate forest	Warm summers and cool to cold winters; clear seasons	Moderate (roughly 750–1500 mm), through the year
Taiga (boreal forest)	Long, very cold winters; short, cool summers	Low to moderate, much falling as snow
Grassland	Warm to hot summers; temperate grasslands have cold winters	Low to moderate, with a dry season; too dry for forest
Tundra	Very cold, below 0 °C for most of the year; permafrost	Very low (often under 250 mm), short growing season
Hot desert	Very hot by day, cool at night: large daily range	Very low (under 250 mm), unpredictable

Common mistake:

A biome is not a single ecosystem. It is a group of ecosystems in different places that share similar communities because their climate is similar.

Written and checked against the IB Biology SL specification · Updated October 2026

Frequently asked questions

What is the difference between a habitat and a niche?

A habitat is the place where an organism, population, species or community lives, such as a sand dune. A niche is the role of a species in its ecosystem, including how it obtains food and all the biotic and abiotic interactions that affect its growth, survival and reproduction. Several species can share a habitat but not a niche.

How is marram grass adapted to sand dunes?

Marram grass rolls its leaves so the stomata, which sit in pits among hairs on the inner surface, are surrounded by humid air, reducing transpiration. A thick waxy cuticle covers the outer surface. Long roots and vertical rhizomes reach deep water and grow upwards when sand buries the plant.

What conditions do coral reefs need to form?

Coral reefs need shallow, clear water so light reaches the photosynthetic zooxanthellae in the corals. The water must also be warm, best at about 23 to 29 °C, of normal seawater salinity and slightly alkaline, so that carbonate ions are available for building calcium carbonate skeletons. That is why reefs are found mainly in shallow tropical seas.

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