Topic 2.4:
Biomes,
zonation and
succession
Starter:
Using the world map outline try
break the world up into its
different biomes.
Shade them in different colours.
E.g. Tropical rainforest, Desert,
Tundra, Savana, Deciduous forest.
Biomes:
• A collection of ecosystems sharing similar climatic
conditions, e.g. tundra, tropical rainforest, desert.
• Although opinions vary we will focus on 5 major
types of biome:
•
•
•
•
•
Aquatic (may split this into freshwater and marine)
Forest
Grassland
Desert
Tundra
Aquatic
Different factors govern the
distribution of biomes.
• Insolation (the amount of suns energy reaching the
surface)
• It is measured by the amount of solar energy received
per square centimeter per minute.
• Precipitation
• Usually measured in mm per meter squared.
• Temperature
• Usually measure in degrees Celsius.
For Homework:
1.
2.
3.
Have a shaded world map with the major biomes labelled.
Find a city in each biome (except polar) and draw its location on your
map, and write down the mean annual temp and precipitation.
Choose 2 pairs of contrasting biomes. Possibilities include…
1.
2.
3.
4.
5.
6.
4.
Temperate forest and Topical forest
Tundra and desert
Tropical coral reefs and Hydrothermal vents
Temperate bogs and tropical mangrove forests
Grasslands and temperate forest
???
Compare and contrast including information on
1.
2.
3.
Characteristic limitation
Productivity
Biodiversity
Why do the biomes
form in these areas?
The tri-cellular model of
atmospheric circulation.
• The distribution of biomes can be understood by
looking at patters of atmospheric air circulation.
1
• The ITCZ (Inter Tropical Convergence Zone)
• Due to the high insolation the air is heated up and
becomes less dense.
• High heat also causes high amounts of evaporation,
this condenses to form large cumulonimbus clouds.
This causes a lot of precipitation.
2
• At around 30o North (and South) the air cools and
forms an area of high pressure.
• This means little cloud formation, therefore low
amount of precipitation.
• The air is still relatively hot here.
3
• As the air move more North it meets cooler air from
the polar regions.
• The polar air is colder and more dense and this pushes
up the relatively warmer air of the Ferrell cell upwards.
• This again causes a large amount of cloud formation,
and therefore precipitation
Limitations:
• Ignores other major transfers of energy e.g. El Nino
and La Nina.
• Ignores geomorphological factors such as mountains.
• Ignores the redistribution of heat and energy via our
oceans.
How will climate change alter the
distribution of the biomes?
Prediction:
Explanation:
Changing biomes
• Deserts are expanding
• Grasslands are increasing
Zonation
• Each species
has an
ecological
niche.
• The niches
change as
we increase
the altitude.
• Temperature
• Precipitation
• Solar
insolation
• Soil type
• Species
interactions
Before we move on to succession, you
need to understand the concept of:
K and r reproductive strategies
• We saw these population
growth curves before.
• S-shape curve represents
a population that is at
carrying capacity (Kstrategy species)
• J-shape curve represents
a population existing in an
exponential phase of
growth (r-strategy
species)
What are K and r?
• The two variables that define a population curve.
• r = growth rate
• K = carrying capacity
K-strategist
• Long life
• Slower growth
• Late maturity
• Fewer, but large offspring
• High parental care and
protection
• High investment in
individual offspring
• Adapted to stable
environment
• Later stages of succession
• Niche specialist
• Predators
• Regulated mainly by
internal factors
• Higher trophic level
r-strategist
• Short life
• Rapid growth
• Early maturity
• Numerous and small
offspring
• Little parental care or
protection
• Little investment in
individual offspring
• Adapted to unstable
environment.
• Pioneers, colonizers
• Niche generalists
• Prey
• Regulated mainly by
external factors
• Lower trophic level
Succession
Succession
Types of succession
• Primary succession – colonisation of bare inorganic
surfaces
• Occurs on new land e.g. after volcanic eruptions and
sand dunes
• Secondary succession – when an already
established community is suddenly destroyed
• Soils are already developed
• E.g. Forest fire, abandoned crop fields
Stages of Succession
Bare, inorganic
surface
Stage 2 –
Establishment
Stage 1 –
Colonization
Stage 4 –
Stabilization
Stage 3 Competition
Climax
community
Activity:
• Using sand dunes as an case study create a poster
outlining the stages of succession.
Oldest
• For each of the 5 stages outline how the following
change:
• Size and diversity of organisms
• Complexity of energy flows
• Soil
• NPP and GPP (explain why they change)
• Productivity : respiration ratio
Youngest
Disturbance in succession
Climax communities
• Not necessarily dense forest.
• There is no one climax community.
• Many stable alternatives
• Dependant on:
• Climatic factors
• Soil properties
• Random events
• Complex ecosystems are more stable due to the
variety of nutrient and energy pathways.
• If one collapses its overall effect is low as there are many
others to takes its place.
Human interference
• Humans can have a huge effect on succession and
influence what becomes the most stable state.
• E.g. Grazing, deforestation, fires