AQA A2 GEOGRAPHY: ECOSYSTEMS

ECOSYSTEMS

Ecosystem basics

An ecosystem is a set of relationships between all the organisms and non-living factors in a particular area. Organisms = biotic factors, non-living = abiotic factors.

The organisms depend on physical factors and each other to survive, so relationships between organisms are important. They vary in size, for example a pond to a forest or ocean.

A biome is an area with a distinctive climate and vegetation, for example a savannah. They can contain different ecosystems within them, and usually cover a large area, often spanning multiple countries.

Energy flows

Energy moves between the organisms in an ecosystem. It enters by photosynthesis- plants use energy from sunlight to grow and reproduce.

The energy is stored in the plant and passed up the food chain when the plant is eaten. When one organism eats another it receives energy from that organism, which means that energy flows between all the organisms in an ecosystem.

Food chains and food webs

These show how energy moves through an ecosystem. Each stage in food chain or web is called a trophic level.

Producers (e.g. plants) occupy the first trophic level; they make their own food.

Primary consumers (herbivores/omnivores) occupy the next level; eat producers.

Secondary consumers (carnivores/omnivores); eat consumers.

Tertiary consumers (top carnivores/omnivores); eat consumers.

The biomass (total mass of living matter) decreases at each trophic level; a field of dandelions feeds a family of rabbits, which can all be eaten by one fox.

Food chains show one way in which the energy is passed from a producer to a consumer. Food webs are more complicated, by showing multiple food chains and demonstrating different ways energy flows through an ecosystem.

Loss of energy

As you go up the trophic levels in a food chain, the amount of energy at each level decreases (around 90% at each level).

1.              Energy lost between sunlight and autotroph. Less than 50% of sunlight is used for photosynthesis, due to light falling on stem/trunk, and plants only being able to use certain wavelengths of light.

2.              Energy lost by the consumers. Only about 10% of energy stored by autotrophs is passed to herbivores, 10% from these to carnivores etc. This is because some parts of the organisms aren't eaten (e.g. roots/bones), some energy is lost as waste (e.g. droppings), and consumers use some of the energy for movement and body heat.

Nutrient cycle

Living organisms need large quantities of carbon, hydrogen, oxygen, nitrogen, sulphur etc. These elements are constantly being recycled through ecosystems, between plants, animals and the atmosphere.

1.     Plants take CO2 from air and nutrients from soil (e.g. nitrogen), to create plant material.

2.     These nutrients get passed along food chains by feeding.

3.     When organisms die they’re broken down by decomposers (e.g. bacteria). Nutrients returned to soil to be used again by plants.

4.     Plants,…