Zonation (HL IB ESS OLD COURSE - IGNORE)
Revision Note
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
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
Worked Example
Investigate changes in the distribution of a species along an environmental gradient.
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
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