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. Have a shaded world map with the major biomes labelled.

2. Find a city in each biome (except polar) and draw its location on your map, and write down the mean annual temp and precipitation.

3. Choose 2 pairs of contrasting biomes. Possibilities include…1. Temperate forest and Topical forest2. Tundra and desert3. Tropical coral reefs and Hydrothermal vents4. Temperate bogs and tropical mangrove forests5. Grasslands and temperate forest6. ???

4. Compare and contrast including information on 1. Characteristic limitation2. Productivity3. 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.

• 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.

1

• 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.

2

• 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

3

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

• Each species has an ecological niche.• The niches

change as we increase the altitude.• Temperature• Precipitation• Solar

insolation• Soil type• Species

interactions

Zonation

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 (K-strategy 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

Time

• Secondary succession – when an already established community is suddenly destroyed• Soils are already developed• E.g. Forest fire, abandoned crop fields

Bare, inorganic surface Stage 2 – Establishment Stage 4 – Stabilization

Stages of Succession

Activity:• Using sand dunes as an case study create a poster

outlining the stages of succession.

Oldest

Youngest

• 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

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