Ecosystems (OCR GCSE Geography B)
Revision Note
Written by: Bridgette Barrett
Reviewed by: Jenna Quinn
Interdependence of Ecosystems
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 is the variety of plant and animal species within an ecosystem
The level of biodiversity depends on the climate, available habitats and food sources
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 links can be shown as food chains and food webs
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. 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
Simple Food Chain Diagram
Food webs
The links between the biotic components can also be shown as a food web
Food webs show the complex interaction of plants and animals that feed on each other
Food Web Diagram
Interdependence
The biotic and abiotic parts of the woodland are linked through 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 flight to 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 bloom
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 impacts owls and other birds of prey, that feed on the smaller birds and mammals
In the food web example 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
Select the correct definition of an ecosystem
(1 mark)
A. A type of tourism that protects the environment
B. The interconnectedness of environments
C. The interdependence of plants and animals with the environment they live in
D. The place where plants and animals live
Answer
C. The interdependence of plants and animals with the environment they live in (1)
The alternative answers are incorrect because:
A: This is ecotourism
B: It is not interconnectedness between environments
D: This is a habitat
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, e.g. 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, e.g. fertilisers/herbicides/pesticides
Fires used to clear land
Global Distribution of Biomes
There are 11 biomes in Earth's biosphere
Biome distribution
Biome distribution is closely linked to climate
There are various factors that impact on climate characteristics including:
Latitude: Temperatures and sunshine hours decrease with distance from the equator
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
Distribution of the World's Biomes
Biome Characteristics
Characteristics of the World Biomes
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 Southeast 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 are 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 Baobab and Acacia trees 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 foxes, polar bears, penguins, caribou |
Worked Example
Study Fig. 3, a map showing the global distribution of coral reefs. Using Fig. 3, describe the global pattern of coral reefs
(3 marks)
Figure 3 - Distribution of the coral reefs
Two marks are awarded for describing the pattern
One mark is awarded for communicating the answer in an appropriate and logical way
Answer
In a band mostly between the Tropics of Cancer and Capricorn (1) with a large concentration over South East Asia (1) (C)
Coral reefs are distributed in North East Australia (1) and around Indonesia (1)
Coral reefs are distributed between 30 degrees N and 30 degrees S (1) and between the Tropic of Cancer and Capricorn (1).
Examiner Tips and Tricks
You may be asked to describe and explain the distribution of biomes. Consider the following;
Biome distribution
Latitude
Country and continent names
Factors which affect the distribution - latitude, altitude, ocean currents, continentality
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