Ecosystems (AQA GCSE Geography)

What is an ecosystem?

• An ecosystem is the living (biotic) and non-living (abiotic) components of an ecosystem 
• Ecosystems vary in size and scale 
  • A small ecosystem could be a garden pond
  • A large-scale ecosystem could be all tropical rainforests - this is known as a biome
• Biodiversity refers to the variety of plant and animal species within an ecosystem
  • The level of biodiversity depends on the climate, available habitats and food sources

What is interdependence?

• Within an ecosystem, the different biotic components depend on each other, and the abiotic components for survival (food, water and shelter)
• This is known as interdependence
  • It means that changes in one component can have significant impacts on other parts of the ecosystem
• One of the main interactions between biotic components is feeding
  • These interactions can be shown as food chains and food webs

Food webs and chains

• Within all food chains and food webs there are examples of:
  • Producers: Food chains always start with a producer
  • Primary consumers: Producers are eaten by primary consumers (herbivores/omnivores)
  • Secondary consumer: Primary consumers are eaten by secondary consumers (carnivores/omnivores)
  • Tertiary consumer: Secondary consumers are eaten by tertiary consumers (carnivores/omnivores)
• There are also decomposers.
• These are fungi and bacteria, and they:
  • Help to return energy/nutrients back to the soil
  • Break down dead organic matter plant/animal waste
  • Release energy from organic matter so it can be recycled

Food chains 

• A food chain shows the feeding interactions and transfer of energy from one organism to the next
• The source of energy in a food chain is light energy from the sun

An example of a food chain

Food webs

• The links between the biotic components can also be shown as a food web
• These show the complex variety of plants and animals which feed on each other

A food web shows the interdependence of organisms

• For example, in the food web above, if the population of caterpillars decreased:
  • The population of grass plants would increase as there are now fewer species feeding off them
  • The populations of sparrows would decrease significantly as earthworms are their only food source
  • The population of hawks would decrease slightly as they eat sparrows but also have another food source to rely on (mice and frogs)

• A deciduous woodland is an example of a small-scale ecosystem in the UK
• It provides a variety of habitats for plants, insects and animals
• Producers include:
  • Tree species: Elm, beech, oak and ash
  • Other plants: Holly, fern, bluebells, wild garlic
  • There are also lichens, mosses 
• Primary consumers include:
  • Insects
  • Rabbits
  • Deer
  • Squirrel (though they may eat larvae/caterpillars if conditions are harsh)
• Secondary consumers include:
  • Frogs
  • Voles
  • Fox
  • Badgers
• Tertiary consumers include:
  • Foxes
  • Birds of prey such as kestrels

Deciduous forest food web

• Animals can be in more than one trophic level: For example, a fox will eat both primary consumers such as rabbits and secondary consumers such as voles
• There are also many decomposers (fungi) which are vital to the nutrient cycle

Deciduous forest nutrient cycle

Interdependence

• The biotic and abiotic parts of the woodland are linked through the nutrient cycle and food webs
• Trees such as the rowan rely on birds eating the berries to disperse their seeds
  • Some berries are dropped during the flight in a new location
  • The seeds have an indigestible coating which means that seeds which are eaten are deposited in droppings
• Oak trees rely on squirrels burying the acorns to store for winter. Acorns which are forgotten then germinate
• The trees in the woodland are mostly deciduous which means that they lose their leaves covering the ground with a thick layer which then decomposes adding nutrients to the soil
• A shrub layer of brambles, grass, bracken and other plants are the main producers
• In spring before the trees come into leaf more light reaches the woodland floor allowing bluebells and daffodils to flower

Impact of a change

• Deciduous woodlands in the UK have been affected by ash dieback
  
  • Over 1000 species are dependent on ash including wood mice, wrens, bats, lichen and beetles
  • It is a significant tree for about 89 invertebrate species including the endangered Violet Click beetle and the Hawk Moth caterpillar
• The removal and death of ash trees impact all of these species which then has a knock-on effect on the species which feed on them
• Woodpeckers, other birds and small mammals which feed on the insects living on and in ash trees may experience a population decrease
• This would then impact owls and other birds of prey which feed on the smaller birds and mammals

• A stable ecosystem is one where all the biotic and abiotic components are in balance so that the populations remain constant
• This may take hundreds of years to develop but the balance can be disturbed very suddenly
• Disruptions to the ecosystem can be the result of either natural events or the result of human activity
  • Natural events may include:
    • Wildfires caused by lightning
    • Climate change (though it can be argued this is human-induced)
    • Spread of invasive species
    • Disease
    • Extreme weather events: Flood or drought
  • Human activities may include:
    • Deforestation
    • Hunting of animals/birds
    • Introduction of invasive species such as grey squirrels which outcompete red squirrels for food and space. They also carry a disease called squirrel pox which kills red squirrels but not grey squirrels
    • Hedgerow removal
    • Changes to water supply/drainage patterns or temperature
    • Addition of chemicals: Fertilisers/herbicides/pesticides
    • Fires used to clear land

• There are 11 biome in Earth's biosphere

Biome distribution

• Latitude: with distance from the equator temperatures and sunshine hours decrease 
• Precipitation: Areas of high pressure experience low rainfall, and areas of low-pressure experience high rainfall
• Altitude: Increases in altitude lead to decreases in temperature
• Continentality: Locations further inland heat up more quickly in the summer and cool more quickly in the winter
• Ocean currents: Warm and cold currents circulate in the oceans either warming or cooling the adjacent land 

World biomes