Deserts and biomes
Deserts cover huge parts of North Africa, the Middle East and central Australia, and these regions are far apart. They share a similar climate, similar plants and similar animals all the same. That pattern is a clue. Somewhere in the way the atmosphere and oceans work, there are controls that decide where dry land forms and where forest grows instead.
Deserts are a good starting point for studying those controls. Once you can explain why a desert sits where it does, you can use the same factors (latitude, air pressure, ocean currents, distance from the sea and altitude) to explain any other biome.
Before reading on, try a Think–Puzzle–Explore. Write down what you think you already know about deserts, list the questions that puzzle you (for example, why some deserts are next to the sea), and note how you could find out.
Compare your lists in a small group, then share with the class. Come back to your puzzles at the end and see which ones you can now answer.
What a biome is
Every living thing sits inside an ecosystem, and ecosystems come in different sizes. The smallest unit is a niche. The largest is a biome.
A very large area with the same or similar vegetation and animal life, classified by its vegetation type and its climate. It is the largest unit on the ecosystem scale.
A biome is made of two kinds of component that constantly affect each other.
The nonliving parts of an ecosystem, such as temperature, rainfall, sunlight, soil and rock.
The living parts of an ecosystem, such as plants, animals and microorganisms.
In a desert, for example, the abiotic conditions (very little rain, intense heat) limit which plants can survive. The plants then limit which animals can live there. Humans are part of this system too, and in many biomes people have changed these interactions, sometimes with harmful results. That story belongs to the lesson on human impact on biomes.
Biomes can be terrestrial (on land) or aquatic (in water). A terrestrial biome may stretch across a large part of a continent, and an aquatic biome may cover a whole region of a sea or ocean. The same biome type appears in several parts of the world where conditions are alike. Rainforest is found in the Amazon, and also in Africa and Asia. Desert is found in Africa, Asia and Australia.
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