Walk from the top of a rocky beach down to the water and the life changes in bands you can actually see: lichen, then barnacles, then seaweed, then anemones. Nothing organised those bands on purpose. They appear because the conditions change gradually as you walk, and each species can only tolerate part of that range.
📚 What you need to know
Zonation is the change in species and communities across space, following a gradient of environmental factors.
Gradients come from things like altitude, latitude, tidal level, soil horizons, distance from water, temperature, moisture and light.
Zones appear because abiotic conditions change and each species has a range it can tolerate; biotic interactions such as competition sharpen the edges.
The classic example is the rocky intertidal zone, from the spray zone down to the low tide zone.
Zonation is measured with a transect, sampling with quadrats at set intervals, recording biotic and abiotic data together.
Results are often drawn as a kite diagram, which shows distribution and abundance at the same time.
Zonation is change over space. Succession is change over time. Do not swap them.
What zonation actually is
Zonation is the gradual change in the mix of species you find as you move across a landscape, driven by a gradient in one or more environmental factors. Because the change in conditions is continuous, but each species has limits it cannot cross, what you end up seeing is a series of bands.
One sentence definitionzonation = the change in species composition across space, along a gradient of environmental factors
Gradients that produce visible zonation include:
Altitude — temperature drops as you climb a mountain, so the vegetation changes with height
Latitude — the global version of the same idea (this is the biome pattern from the last sub-topic)
Tidal level — how long a spot spends underwater each day
Soil horizons — conditions change with depth through the soil profile
Distance from a water source — a river bank, a pond edge, a sand dune system
Temperature, moisture and light — the three that most directly limit plant growth
Both halves matter. Abiotic factors set the outer limits of where a species could live. Biotic factors such as competition and predation then decide where it actually lives. That is why the boundaries between zones are often sharper than the change in conditions.
The rocky shore: zonation you can see
On a rocky shore the master factor is how long each patch of rock spends out of the water. That single gradient runs from the high tide mark to the low tide mark and produces bands you can pick out from a distance.
The top of the shore is limited by physical stress — drying out. The bottom is limited by biology — competition and predation. That is why the upper limit of a species is usually set by abiotic factors and the lower limit by biotic ones.
If you can only remember one shore fact, remember that one: top of the shore, the sun kills you; bottom of the shore, your neighbours do.
Zonation is not succession
These two get mixed up in almost every class. The difference is simple once you see it written down.
Question
Zonation
Succession
Change over what?
Space — distance across a landscape
Time — years or centuries in one place
What causes it?
An existing environmental gradient
The community changing its own environment
What you see
Bands existing side by side, all at once
One community replacing another, one after the other
Typical example
Bands up a rocky shore or a mountain
Bare rock becoming forest
How you study it
A transect across the gradient
Repeat surveys, or comparing sites of different ages
Measuring zonation: transects and quadrats
A transect is a line laid across the gradient. You sample along it so that your data follow the change in conditions instead of ignoring it.
Line transect — record only the organisms actually touching the line.
Belt transect — place a quadrat at intervals along the line and record everything inside it. This is the one you will usually describe.
Continuous sampling means quadrats touching all the way along; interrupted means quadrats at fixed intervals, which is faster over long distances.
🧩 Method: investigating a species along a gradient
Lay the transect along the gradient, not across it — for example a 30 m tape running straight up a hillside from the path.
Place a quadrat at equal intervals, say every 5 m, so the sampling is systematic rather than random. Zonation questions need systematic sampling, because you want the pattern, not an unbiased average.
Record the biotic data in each quadrat: the number of individuals, or percentage cover if the species is hard to count.
Record an abiotic factor at the same points — altitude, soil moisture, pH, light. Without this you can describe a pattern but not explain it.
Repeat with several transects across the site, so your result is not a fluke of one line.
Plot and describe. Abiotic factor on the x-axis (independent), species count on the y-axis (dependent).
Describing this in an exam: as altitude increases, the number of plants decreases. Then explain it — higher up is colder, windier and the soil is thinner, so fewer individuals can survive.
Kite diagrams
A scatter graph handles one species at a time. A kite diagram shows several species along the same transect at once, so you can see how their zones overlap.
Each species gets its own horizontal strip, with a central line.
Distance along the transect runs along the x-axis, parallel to that central line.
Abundance is shown by the width of the shape around the central line.
It is called a kite because the shape extends an equal distance above and below the line.
An extra strip can be added on top for an abiotic factor, such as elevation or soil pH, so you can line the pattern up against its cause.
Read it as three zones with fuzzy edges: marram holds the bare, salty sand nearest the sea, sea couch takes the middle, and brambles dominate the sheltered end where soil has built up.
Worked examples
EXAM Q1
Explain why distinct zones of organisms are found on a rocky shore. [4]
Point 1: name the gradient
Moving up the shore, the time spent out of the water increases.
Point 2: abiotic effect
Higher up means more drying out, bigger temperature swings and more exposure to sun and air.
Point 3: tolerance ranges
Each species survives only part of that range, so it is limited to a band.
Point 4: biotic effect
Lower down, competition for space and predation set the limit instead.
A gradient plus different tolerance ranges gives visible bands“explain” means say why the band exists, not just list what lives in it
EXAM Q2
Describe the relationship shown in the hillside transect graph above. [2]
Step 1: state the direction
As altitude increases, the number of plants per quadrat decreases.
Step 2: quote data as support
The count falls from about 78 at 3 m to about 11 at 21 m.
A negative relationship, supported with figures from the graph“describe” wants the pattern plus data; save the reasons for “explain”
EXAM Q3
Outline how you would investigate whether soil moisture affects the distribution of a plant near a pond. [3]
Step 1: set up the transect
Run a tape from the water’s edge outwards, along the moisture gradient.
Step 2: sample systematically
Place a quadrat every 2 m; record percentage cover of the plant and soil moisture at each point.
Step 3: repeat and plot
Repeat along several transects, then plot moisture against cover and describe the relationship.
Transect along the gradient, quadrats at set intervals, both variables recorded togethermeasuring the abiotic factor is the mark most people drop
💡 Exam tip
Always name the gradient first. Zonation answers that do not identify the changing factor cannot score the explanation marks.
For method questions, say systematic sampling along a transect. Random sampling would destroy the pattern you are looking for.
Record the abiotic factor as well as the organisms — that is what turns a description into an explanation.
Use percentage cover for plants that spread, and counts for individuals you can separate.
On a kite diagram, remember width equals abundance and position equals distribution. Questions ask for both.
Repeat transects to improve reliability; use a larger or more numerous quadrat to improve how representative your sample is.
⚠ Common mix-up
Confusing zonation with succession. Space versus time. Write it on the front of your notes.
Saying species “choose” a zone. They do not choose; they survive where conditions allow and competition permits.
Using random sampling for a transect. Random is for estimating abundance over an area, not for following a gradient.
Reading a kite diagram as height above ground. The vertical width is abundance, not size or height.
Forgetting the biotic half. Competition and predation shape zones just as much as the abiotic gradient does.
Describing a graph as “it goes down” without data. Quote at least one pair of figures.
Up next: Succession and How Communities Change — the same idea, but with time as the gradient instead of distance.
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