Ecosystems (AQA GCSE Geography)
Revision Note
Written by: Bridgette Barrett
Reviewed by: Jenna Quinn
Interrelationships of Ecosystems
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
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
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)
Worked Example
State one role of decomposers in an ecosystem.
[1 mark]
Answer:
Decomposers help to return nutrients/energy to the soil [1]
They break down dead plants and animals/organic waste or excreted material [1]
They release energy from a plant or animal so that it can be recycled [1]
Case Study: UK Ecosystem
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
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
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
Ecosystem Balance
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
Distribution & Characteristics of Biomes
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
Biome | Location | Climate Characteristics | Other Characteristics |
|---|---|---|---|
Tropical Rainforests | Low latitudes within the tropics 23.5° north and south of the equator Found in South America, Asia and Africa | Annual rainfall - 2000mm High temperatures 26-28oC Convectional rainfall | Ideal conditions for plant growth High levels of biodiversity Distinct layers of vegetation |
Tropical Monsoon Forest | 5-30° north and south of the equator Located in India, Central America and South-east Asia | Rainfall between 700-2000mm Temperatures 30-45°C in summer and 15-30°C in winter Monsoon rainfall in the rainy season | High levels of biodiversity Mahogany, teak, lianas, orchids Monkeys, Jaguars, snakes, frogs |
Mediterranean | Approximately 40-45° north of the equator Southern Europe and North Africa | Hot dry summers, wet, mild winters Temperatures usually between 20-25°C. In Winter temperatures are around 10°C Rainfall averages 800mm | Dense scrubland Vegetation includes herbs such as lavender and rosemary Trees include citrus and olives |
Deciduous Forest | Approximately 50° north of the equator Europe and North America | Wet, mild winters and warm, drier summers Average temperature around 10°C with no extremes | Deciduous trees which lose their leaves in winter due to the cooler temperatures - include oak, beech, ash Wide range of animals and plants Deer, rabbits, squirrels, bears |
Coniferous Forest | Approximately 60° north of the equator Northern Europe, Canada and Russia | Cold winters and mild summers Winter temperatures can reach -40°C and summer temperatures 20°C | Many trees are evergreen Include species such as spruce, pine Less biodiversity than temperate forests Bears, squirrels, foxes, wolves |
Savanna (tropical) Grassland | Between 15-30° north and south of the equator South America, Central Africa, Australia | Distinct wet and dry seasons Temperatures vary between 15-35°C Annual rainfall 800-900mm | Dominated by grasses Scattered trees including baobab and acacia Savanna animals include giraffes, lions, zebras, elephants |
Temperate Grassland | Between 30-40° north and south of the equator Southern Africa, Russia, North America | Hot summers 40°C, Cold winters -30°C Annual rainfall 250-750mm a year | Dominated by grasses, very few trees Animals include bison, deer, snakes |
Desert | Approximately 20-30° north and south of the equator Africa, Australia , South and North America | Hot daytime temperatures up to 50°C but average 25°C Night time temperatures below 0°C Precipitation below 250mm | Low diversity Plants include yucca and cacti Animals include spiders, scorpions, camels |
Polar/tundra | Above 60° north and south of the equator Arctic, Antarctic, Northern Canada, Siberia | Cold year round, brief cool summers in tundra areas Below 0° C for 6-10 months Precipitation often below 250mm | Low biodiversity Short growing season Small grasses, lichens and mosses Arctic fox, polar bears, penguins, caribou |
Worked Example
Study figure 1, a world map showing global biodiversity levels
Using figure 1, suggest one reason for high biodiversity levels in area X.
[2 marks]
Your answer needs to give a reason to gain one mark and then an explanation of why this leads to high biodiversity for the second mark
Answer:
Area X receives very high rainfall [1] which allows many plants to grow (d)[1]
Area X experiences high temperatures and high rainfall [1] which means that plants grow rapidly (d) [1]
Area X receives some rain every month [1] which means that plants grow throughout the year (d) [1]
There is a hot wet climate [1] which leads to the growth of many plants in a tropical rainforest (d) [1]
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