Zonation (DP IB Environmental Systems & Societies (ESS))

Zonation

• Zonation refers to the gradual change in the composition of species and communities across a landscape, based on a gradient of environmental factors such as:

  • Elevation (altitude)

  • Latitude

  • Tidal level

  • Soil horizons

  • Distance from water source

  • Temperature

  • Moisture

  • Light

• As these factors change, the species present in an ecosystem also change

  • This leads to distinct zones or bands of organisms that can be observed in the ecosystem

  • This process occurs due to the interactions between the physical environment (abiotic factors) and the biological components (biotic factors) of an ecosystem

• An example of zonation can be observed in a rocky intertidal zone

  • Here, the physical and biological characteristics of the ecosystem change gradually from the high tide mark to the low tide mark

    • At the highest point (sometimes referred to as the spray zone), the zone is usually dry and dominated by lichen and other hardy plants that can withstand long periods of exposure to air and sunlight

    • In the high tide zone, the environment becomes more hospitable for other organisms such as barnacles, mussels, chitons, limpets and sea snails that can attach themselves to the rocks and withstand waves

    • Further down towards the low tide zone, the environment becomes even more favourable for marine organisms such as sea stars, anemones, and sea urchins that require the constant presence of water

Transects

• Transects can be used to measure biotic and abiotic factors along an environmental gradient

  • This data can be used to determine the variables that affect the distribution of a species

Representing results

• The results of an investigation into the distribution and abundance of organisms can be represented visually using a type of graph known as a kite diagram

• Kite diagrams can show both distribution and abundance

  • The distribution of a species along a transect can be shown by its position along a central horizontal line in each section of a kite diagram

  • Each section represents a different species  

  • The distance along the transect is given on the x-axis, to which the horizontal line is parallel

  • The abundance of a species can be shown by the width of the 'kite' around the central horizontal line

  • The shape is referred to as a kite because it extends an equal distance on each side of the central horizontal line

• Additional sections can be added to a kite diagram to show the changes in abiotic factors at different points along a transect e.g. the height above sea level or the pH of soil