Ecosystems (AQA GCSE Geography): Revision Note

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)

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 and characteristics of biomes

• There are 11 biomes 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 

Tropical rainforest

• Location

  • Low latitudes within the tropics 23.5^° north and south of the equator  

  • Found in South America, Asia and Africa

• Climate characteristics

  • Annual rainfall - 2000mm

  • High temperatures 26-28^oC

  • Convectional rainfall

• Other characteristics

  • Ideal conditions for plant growth

  • High levels of biodiversity

  • Distinct layers of vegetation

Tropical monsoon forest

• Location

  • 5-30^° north and south of the equator

  • Located in India, Central America and South-east Asia

• Climate characteristics

  • Rainfall between 700-2000mm

  • Temperatures 30-45°C in summer and 15-30°C in winter

  • Monsoon rainfall in the rainy season

• Other characteristics

  • High levels of biodiversity

  • Plants and trees include mahogany, teak, lianas and orchids

  • Monkeys, Jaguars, snakes, frogs

Mediterranean

• Location

  • Approximately 40-45^° north of the equator

  • Southern Europe and North Africa

• Climate characteristics

  • Hot dry summers, wet, mild winters

  • Temperatures usually between 20-25^°C. In Winter temperatures are around 10^°C

  • Rainfall average 800mm

• Other characteristics

  • Dense scrubland 

  • Vegetation includes herbs such as lavender and rosemary

  • Trees include citrus and olives

Deciduous forest

• Location

  • Approximately 50^° north of the equator 

  • Europe and North America

• Climate characteristics

  • Wet, mild winters and warm, drier summers

  • Average temperature around 10^°C with no extremes

• Other characteristics

  • 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

• Location

  • Approximately 60^° north of the equator 

  • Northern Europe, Canada and Russia

• Climate characteristics

  • Cold winters and mild summers

  • Winter temperatures can reach -40^°C and summer temperatures 20^°C

• Other characteristics

  • Many trees are evergreen 

  • Include species such as spruce, pine

  • Lower biodiversity than temperate forests

  • Bears, squirrels, foxes, wolves

Savanna (tropical) grassland

• Location

  • Between 15-30^° north and south of the equator

  • South America, Central Africa, Australia

• Climate characteristics

  • Distinct wet and dry seasons

  • Temperatures vary between 15-35^°C

  • Annual rainfall 800-900mm 

• Other characteristics

  • Dominated by grasses

  • Scattered trees including baobab and acacia

  • Savanna animals include giraffes, lions, zebras, elephants

Temperate grassland

• Location

  • Between 30-40^° north and south of the equator

  • Southern Africa, Russia, North America

• Climate characteristics

  • Hot summers 40^°C, Cold winters -30^°C

  • Annual rainfall 250-750mm a year

• Other characteristics

  • Dominated by grasses, very few trees

  • Animals include bison, deer, snakes

Desert

• Location

  • Approximately 20-30^° north and south of the equator

  • Africa, Australia , South and North America

• Climate characteristics

  • Hot daytime temperatures up to 50^°C but average 25^°C

  • Night time temperatures below 0^°C

  • Precipitation below 250mm

• Other characteristics

  • Low diversity

  • Plants include yucca and cacti

  • Animals include spiders, scorpions, camels

Polar/tundra

• Location

  • Above 60^° north and south of the equator

  • Arctic, Antarctic, Northern Canada, Siberia

• Climate characteristics

  • Cold year round, brief cool summers in tundra areas

  • Below 0^° C for 6-10 months

  • Precipitation often below 250mm

• Other characteristics

  • Low biodiversity

  • Short growing season

  • Small grasses, lichens and mosses

  • Arctic fox, polar bears, penguins, caribou